10, 1995. Thermodynamic Parameters for the Interaction of. Adenosine 5'-Diphosphate, and Adenosine. 5'-Triphosphate with Mg 2+ from 323.15 to 398.15 K.
Journal of Solution Chemistry, Vol. 24, No. 10, 1995
Thermodynamic Parameters for the Interaction of Adenosine 5'-Diphosphate, and Adenosine 5'-Triphosphate with Mg 2+ from 323.15 to 398.15 K E Wang, 1 J. L. Oscarson, 1 R. M. Izatt) ~ G. D. Watt, 1 and C. D. Larsen I Received May 16, 1995; revised August 25, 1995 The htteraction of adenosine 5'-dipho~phate (ADP) and adenosine 5'-tripho,~phate (ATP) with Mg 2+ in water has been studied calorimetrically at 323.15, 348.15, 373.15, and 398.15 K for ATP and at 348.15 and 373.15 K for ADP. The enthalpies o f reaction o f Mg 2+ with ADP and ATP were obtained from the heats of mixing o f aqueous solutions o f tetramethylammonium salts o f ADP and ATP with MgCl z solutions in an isothermal flow calorimeter. Equilibrium constant (K), enthalpy change (AH~ entropy change (AS~ and heat capacity change (ACp~ values were calculated for the interaction: Mg 2+ + L n- = MgL 2-~ and Mg 2§ + MgL 2-n = Mg2L4-", where n = 4 f o r L = A T P a n d n = 3 f o r L = ADP. The results are consistent with those at lower temperatures. For the two nucleotides studied, the above two reactions are endothermic and entropy-driven in the temperature range studied. Large ACp~valuesfor the interaction of Mg 2+ with ADP with ATP indicate the involvement o f phosphate groups o f nucleotides in the coordination o f Mg z+. The coordination o f the first and second Mg 2+ ions involves the phosphate chain in both ADP and ATP. No evidence was found for the involvement o f the adenine ring or the ribose moiety in the coordination o f Mg 2+ with these nucleotides. Approximate values o f log K, AH~ and AS", and ACp~ for the self-association o f ADP and ATP in the presence o f Mg 2+ are also given.
KEY WORDS: Equilibrium constants; enthalpies; entropies; heat capacities;
adenosine-5'-di- and triphosphate; Mg2+; temperature dependence; heats of reaction.
~Departments of Chemistry. and Chemical Engineering, Brigham Young University, Provo, Utah 84602. 2To whom correspondence should be addressed at Department of Chemistry, Brigham Young University, Provo, Utah 84602. 989 0020-774819511000-0989507.50/0 9 1995 P~enum Publishing Corporation
990
Wang, Oscarson, Izatt, Watt, and Larsen
1. ~ T R O D U C T I O N The adenine nucleotides are present in the aqueous medium of diverse types of cells of organisms and have an important role in the chemical reactions of life. In recent years, there has been increasing interest in the study of interaction of adenine nucleotides with divalent metal ions. The influence of these metal ions on biological reactions has long been known, cl) Much of the interest has been centered on Mg 2+ because it is an essential cofactor for metabolic processes involving energy storage, utilization, and transfer. ~2)A knowledge of the energetics of the interactions of Mg z+ with nucleotides and nucleic acids in aqueous solutions has been essential in understanding energy production in living organisms at ambient temperatures. A quantitative knowledge of the speciation and driving forces for the metal-nucleotide complexation as a function of temperature should be helpful in a search for an understanding of the ability of organisms to survive in high temperature/pressure environments33) In addition, extrapolation of thermodynamic values from low to high temperatures is uncertain without reliable extrapolation procedures and high temperature data to guide the extrapolation. Therefore, it seemed desirable to study the systems of interest directly at elevated temperatures. The structures for ADP and ATP are shown in Fig. 1. The thermodynamic values, K, AH~ AS~ and ACp~ for the interaction of these species with Mg 2§ should provide information concerning the speciation, reaction driving forces, site of Mg 2+ coordination with the ligand, and the extent of water interaction with the complexed and uncomplexed species. Values of log K, A/F, and AS~ for interaction of ADP and ATP with Mg 2+ at temperatures below 338 K have been reported34-9) Reviews and compilations of thermodynamic quantities for interaction of protons and metal ions with nucleotides are available31~ The reported log K values are in reasonable agreement. However, the A/-/~ values are not in good agreement, possibly due to the different media used in the experiments and the different ionic strengths at which the A/-F values were measured. No A/F, AS~, or ACp~ values have been reported for the interaction of ADP and ATP with Mg z+ at temperatures above 323.15 K. Few log K values were reported from 323 to 338 K. ~lz) The use of supporting electrolytes, such as KNO3, NaCI, and NaC104 in some of the measurements introduces K § and Na § which interact with the phosphate groups of the ribonucleotides. Since corrections for these interactions were not made, the resulting thermodynamic values are in error by some unknown amount. Coordination of Mg 2+ with phosphate groups of adenine nucleotides has been studied by 3!p NMR,fS,t4) 17O NMR,!ts) 25Mg NMR,(16~ X-ray diffraction, ~17) infrared and Raman spectroscopy,~18'19) calorimetry, ~7'8) and potentiometry. ~6'9)The general conclusion is that the phosphates of adenine nucleotides
Interaction of ADP and ATP with Mg 2+
991 .I.I.NH2
0 I~
0 II
s'
]
"O---P---O-'-P---O--CH2 ., O - -
I
I
I ),,"
H
~ t
I
I
OH
OH
[ A D P 3"
H
.NH2
O II
O II
o II
5'
I
I
I
I
l /
-O--P.--o--p--o--P~O--CH2., O - -
o
o.
o
~'H HI
]
~ 1
A T P 4"
HN I
OH
I
H
OH
Fig. 1. Structuresof adenosine5'-diphosphate (ADP)and adenosine5'-triphosphate (ATP).
are the effective groups in attracting Mg 2+, i.e. M g 2+ is bound to the oL-phosphate group in AMP, the c~- and B-phosphates in ADP, and either the 1~- and ~/phosphates or o~-,13-and',/-phosphates in ATP in the l: 1 complexes. Suggestions for the structure of the dimagnesium complex of ATP, Mg2ATP, were also given. (8'9A7'2~ Coordination of the second Mg 2+ with ATP also involves the phosphate groups/8,9~17) Results of a kinetic study (2~ suggested that the structures of dimagnesium complexes of these nucleotides may be similar in both di- and triphosphates. Our recent 1H NMR study has given no indication of an interaction between Mg 2+ and the adenine ring in the Mg 2+ complexes of AMP, ADP, or ATP.(21~ A study has been initiated in this laboratory to determine the thermodynamic quantities associated with the interaction of protons and metal ions with compounds of biological interest at elevated temperatures. This paper presents log K, A/P, AS~ and ACp~ values for the interaction of ADP and ATP with Mg 2+ at temperatures up to 125~
992
Wang, Oscarson, Izatt, Watt, and Larsen
2. EXPERIMENTAL 2.1. Materials
ADP disodium salt (Sigma, 95-99%), ATP disodium salt (ICN, 99%), tetramethylammoniumhydroxide [N(CH3)4OH] pentahydrate (Aldrich, 99%), and magnesium chloride hexahydrate (Aldrich, 99%) were used in the preparation of the solutions. The Na + originally present in the ADP and ATP solutions was exchanged for N(CH3)4§ by cation-exchange chromatography to prevent complexing of these nucleotides by Na § After cation exchange, the ADP and ATP solutions were adjusted to pH 8.5 using a known amount of N(CH3)aOH. Concentrations of the ADP and ATP solutions, after cation-exchange and pH adjustment, were then determined by the UV absorbance at 259 nm in a dilute solution (e0 = 15400). All ADP and ATP solutions were freshly prepared and kept at approximately 273 K during the solution preparation. The solutions were made using distilled, deionized water and degassed by submersion in an ultrasonic bath for 5 minutes. 2.2. Procedure
Heat of reaction data for mixing solutions of the tetramethylammonium salts of ADP and ATP with solutions of MgC12were determined using an isothermal flow calorimeter whose construction, operation, and calibration against standard systems have been described. (22~The data were collected at 1.52 MPa and at 323.15, 348.15,373.15, and 398.15 for ATP and 348.15 and 373.15 for ADP. The Mg2+-ADP system could not be studied at 398.15 K due to formation of a precipitate under the experimental conditions. The flow rates of ADP and ATP solutions were set at a constant value for each run at each temperature, and those of the MgCI2 solutions were varied so that molar ratios of MgClz:ADP or MgClz:ATP ranged from 0.2:1 to 4:1. Each reaction run was repeated at least two times. The standard deviations for the duplicated runs are less than 0.02 J-min- 1.The enthalpy data were obtained by averaging the values for each pump setting from the repeated runs. Table I summarizes the systems and experimental conditions for the present study. 2.3. Calculations
A computer program and an optimization routine(23'24)were used to analyze the experimental heat of reaction data and to find the log K and AH~ values valid at infinite dilution at each temperature which gave the best agreement between the predicted and the measured heats. Activity coefficients, based on Lindsay's modified Meissner model, were calculated in the program and were used for the correction of heats of dilution. Details of the data analysis method are available. (23)
Interaction of ADP and ATP with Mg 2+
993
Table I. Summaryof Systems Studied and Experimental Conditions~
System
T(K)
Concentration of solutions (mol'kg-~) Nucleotide MgC12
ADP + MgCI2
348.15 373.15
0.03122 0.03944
0.1018 0.1014
ATP + MgClz
323.15 348.15 373.15 398.15
0.03655 0.03655 0.03655 0.03863
0.1085 0.1085 0.1085 0.1085
~AI1determinations were made at 1.52 MPa. The ionization equilibria during mixing of MgCt2 with A D P and MgCI2 with ATP can be expressed as reactions 1 through 4 and 5 through 8, respectively. ADP 3- + Mg 2+ = M g A D P -
(1)
M g A D P - + Mg 2+ = Mg2ADP +
(2)
ADP 3- + H + = H A D P 2-
(3)
H A D P 2- + Mg 2+ = M g H A D P
(4)
ATP 4- + Mg 2+ = MgATP 2-
(5)
MgATP 2- + Mg 2+ = Mg2ATP
(6)
ATP 4- + H + = HATP 3-
(7)
HATP 3- + M g 2+ = M g H A T P -
(8)
These reactions were used in the analysis of the ADP and ATP data together with the self-association reactions M g A D P - + M g A D P - = (MgADP)22-
(9)
MgATP a- + MgATP 2- = (MgATP)24-
(10)
The log K and AH ~ values for the protonation reactions (3) and (7) used in our data analysis were taken from our earlier study. (25)The inclusion of reaction (4) for the analysis of ADP data and of reaction (8) for the analysis of ATP data did not improve the results and in some cases gave poorer fits to the experimental heat of reaction data. The pH range in our study was between 6.5 and 8.5. Over this pH range, our calculations showed that monoprotonated A D P and ATP do not react significantly with Mg 2§ Therefore, reactions (4) and (8) were discarded in our final data reduction. The self-association of ADP and ATP has been reported. (18,26-29~ The presence of Mg 2+ promotes the self-stacking
994
Wang, Oscarson, Izatt, Watt, and Larsen
tendency of these adenine nucleotides.(26,27)Our 1HNMR study of Mg 2+ interaction with AMP, ADP, and ATP~21~provides evidence of the self-association of these nucleotides at nucleotide solution concentrations as low as 0.005M upon addition of Mg 2§ The addition of Mg 2§ to the ADP and ATP solutions favors self-stacking by a factor of about 3 in the self-association constant K for both nucleotides.(26,27)This promotion of the self-stacking is due to partial neutralization of the negative charge at the phosphate moiety by formation of a Mg 2+ complex. Using the self-association constants for the MgADP- and MgATP2systems reported by Scheller et a/., (26'27) the calculated concentrations of the MgADP- and MgATP2- monomers are less than 78% and 86% of the total concentrations, respectively, over the concentration and pH ranges studied. Therefore, self-association of MgADP- and MgATP2- were included in our calculations. Under our experimental conditions, the self-association beyond the dimer stage can be ignored. Inclusion of the self-association reactions in our calculation slightly improved the fits for both ADP and ATP data. The pressure effect on the interaction was ignored in the present study, since the pressure effect on interaction of protons with these nucleotides and phosphate ions in the same temperature range was within experimental error up to 12.5 MPa323.25)
3. R E S U L T S A N D D I S C U S S I O N
The calorimetric data are given in Table II for the reaction of ADP with MgCI2, in Table Ill for the reaction of ATP with MgC12, and in Table IV for the dilution of MgCI2 and of the tetramethylammonium salt of ATP. The log K, A/F, AS~ and ACp~values for reactions (1), (2), (5), (6), (9), and (10), together with literature v a l u e s , (12'13'30'31) are given in Tables V and VI. The uncertainties in log K and A/-F were estimated from a statistical t test on the experimental data. The maximum standard deviation of 0.02 J-min- 1found for the duplicated runs was used to determine the 95% confidence level for each experimental point. New input data were generated by adding the resulting value of tl~v/n times the standard deviation to each data point, where n is the number of duplicated runs at each point, and t is the Student's t number for the degrees of freedom ofn - 1 under the 95% confidence level. These new data were used to determine the log K and A/F values for reactions (1), (2), and (9) in the case of the ADP system and for reactions (5), (6), and (10) in the case of the ATP system which would give the minimum difference between the predicted and measured heats. The differences between the thermodynamic values obtained with the modified input data and those reported in Tables II and III were taken to be the uncertainties associated with the log K and AH~ values for the reactions studied. The maximum uncertainties for the log K and AH~ values are given in the footnote
Interaction of ADP and ATP with Mg 2+
Table II.
Flow A a
995
Calorimetric Data for the Reaction of ADP with MgCl2 at Various Temperatures and 1.52 MPa
Flow/T
Qmb
Qcb
T = 348.15K; A = 0.1018mMgC12; B = 0.03122mADP + 0.0935mN(CH3)~ § 0.03171 0.49012 0.06289 0.07705 0.06342 0.49012 0.14272 0.15505 0.09765 0.49012 0.22450 0.23846 0.13357 0.49012 0.32573 0.31842 0.16696 0.49012 0.39112 0.36915 0.20569 0.49012 0.41816 9.39932 0.23997 0.49012 0.41621 0.41575 0.27425 0.49012 0.41349 0.42775 0.30853 0.49012 0.44086 0.43698 0.34281 0.49012 0.45227 0.44424 0.37709 0.49012 0,45400 0,45005 0.41138 0.49012 0.47453 0.45477 0.44566 0.49012 0.45672 0.45863 0.47994 0.49012 0.45389 0.46184 0.51422 0.49012 0.46356 0.46451 0.54850 0.49012 0.47649 0.46677 0.06342 0.65349 0.15510 0.15467 0.09765 0.65349 0.23884 0.23892 0.13357 0.65349 0.31541 0.32596 0.16696 0.65349 0.39752 0.40180 0.20569 0.65349 0.46220 0.47128 0.23997 0.65349 0.51059 0.50874 0.27425 0.65349 0.53992 0.53243 0.30853 0.65349 0.55442 0.54954 0.34281 0.65349 0.56191 0.56290 0.37709 0.65349 0.57266 0.57371 0.41138 0.65349 0.58358 0.58263 0.44566 0.65349 0.58912 0.59010 0.47994 0.65349 0.59172 0.59640 0.51422 0.65349 0.60704 0.60176 0.54850 0.65349 0.59873 0.60636 in Table V. T h e uncertainties in AS ~ and A C p ~ were e s t i m a t e d from those in log K and A H ~ In o r d e r to test the a d e q u a c y o f the activity coefficient m o d e l u s e d in our calculations, heats o f dilution for the t e t r a m e t h y l a m m o n i u m salt o f ATP were m e a s u r e d at 373.15 K, and those for MgC12 were collected at 323.15 and 398.15 K and at 1.52 MPa. In Fig. 2, the m e a s u r e d heats o f dilution w e r e c o m p a r e d with those c a l c u l a t e d using L i n d s a y ' s m o d i f i e d M e i s s n e r m o d e l and l a g K and A/-F values o b t a i n e d from this study. Very g o o d a g r e e m e n t b e t w e e n the m e a sured and c a l c u l a t e d heats o f dilution indicates that the activity coefficient m o d e l used in the calculations is satisfactory for the systems studied.
Wang, Oscarson, Izatt, Watt, and Larsen
996
Table II. Continued Flow A a
Flow Ba
Qb~
Q~
T = 373.15 K; A = 0.1014mMgC12; B = 0.03944mADP + 0.1125mN(CH3)4+ 0.03171 0.48790 0.11974 0.08876 0.06342 0.48790 0.21713 0.17986 0.09766 0.48790 0.31566 0.27932 0.13358 0.48790 0.40995 0.38061 0.16697 0.48790 0.48776 0.45562 0.20570 0.48790 0.52430 0.50058 0.23999 0.48790 0.57291 0.52352 0.30856 0.48790 0.59265 0.55306 0.34284 0.48790 0.59950 0.56309 0.37713 0.48790 0.59102 0.57101 0.41141 0.48790 0.59706 0.57729 0.44569 0.48790 0.59053 0.58232 0.47998 0.48790 0.58596 0.58636 0.51426 0.48790 0.57715 0.58963 0.54855 0.48790 0.58466 0.59230 0.03171 0.65054 G.06541 0.08840 0.06342 0.65054 0.15546 0.17878 0.09766 0.65054 0.25905 0.27781 0.13358 0.65054 0.37161 0.38218 0.16697 0.65054 0.45056 0.47721 0.20570 0.65054 0.54029 0.57493 0.23999 0.65054 0.60407 0.63298 0.27427 0.65054 0.66231 0.66744 0.30856 0.65054 0.68531 0.69136 0.34284 0.65054 0.69444 0.70993 0.37713 0.65054 0.71761 0.72499 0.41141 0.65054 0.72250 0.73741 0.44569 0.65054 0.71549 0.74774 0.47998 0.65054 0.74208 0.75638 0.51426 0.65054 0.73392 0.76362 aUnits: gH20.min-t; bUnits: J-min-1.
Over the relatively narrow temperature range of this study, the e x p e r i m e n tal heat data for the reactions studied were fitted well with Eqs. (11) and ( t 2 ) : logK=a+b/T+clogT AH~ = -2.303 Rb + cRT
(11) (12)
where T is temperature in Kelvins, R is the gas constant, and a, b, and c are fitting parameters. Equation (12) was obtained from Eq. (11) using the Van't Hoff equation. The fitting parameters were adjusted to allow the calculated log K and AH ~ values to fit those reported in the literature at 298.15 K as well as
Interaction of ADP and ATP with Mg 2+
Table III.
Flow A'~
997
Calorimetric Data for the Reaction of ATP with MgCI2 at Various Temperatures and 1.52 PMa Flow Ba
Qmb
Qcb
T = 323.15 K; A = 0.1085m MgClz; B = 0.03655m ATP + 0.1460m N(CH3)4+ 0.03398 0.48517 0.07360 0.07831 0.06796 0.48517 0. t 5276 0.15813 0.10194 0.48517 0.23616 0.23924 0.13591 0,48517 0,31841 0.32036 0,16989 0.48517 0.39022 0.38852 0.20387 0.48517 0.44539 0.42626 0.23785 0,48517 0.47199 0.45579 0.27183 0.48517 0.49141 0.48120 0.30581 0.48517 0.51883 0.50302 0.33978 0.48517 0.51780 0.52158 0.37376 0.48517 0.54445 0.53727 0.40774 0,48517 0.55783 0.55049 0.44172 0,48517 0.56028 0.56164 0.47570 0.48517 0.56632 0.57107 0.50968 0.48517 0.57611 0.57910 0.54365 0.48517 0.58623 0.58597 0.57763 0.48517 0.58737 0.59 190 0.61161 0.485 l 7 0.59994 0.59704 0.64559 0.48517 0.59602 0.60154 0.06796 0.64690 0.14950 0.15738 0.10194 0.64690 0.23028 0~ 0.13591 0.64690 0.31417 0.31899 0.16989 0.64690 0.39218 0.40039 0.20387 0.64690 0.47509 0.47797 0.23785 0.64690 0.54445 0,53284 0.27183 0.64690 0.59292 0,56835 0.30581 0,64690 0,61349 0.59844 0.33978 0.64690 0.65266 0.62528 0.37376 0.64690 0.66963 0,64930 0.40774 0.64690 0,68709 0.67069 0.44172 0.64690 0.70064 0.68964 0.47570 0.64690 0.71745 0.70635 0.50968 0.64690 0.72169 0.72 ~06 0.54365 0.64690 0.72675 0.73399 T = 348.15 K; A = 0.1085m MgCI~; B = 0.03655m ATP + 0.1460m N(CH3)4+ 0.03398 0.48517 0.09953 0.10207 0.06796 0.48517 0.20054 0.20740 0.10194 0.48517 0.30503 0.31489 0.1359 t 0.48517 0.41216 0.42298 0.16989 0.48517 0.51532 0.51523 0.20387 0.48517 0.57302 0.56767 0.23785 0.48517 0.6 1749 0.61148 0.27183 0.48517 0.64923 0.64982
Wang, Oscarson, Izatt, Watt, and Larsen
998 Table lII. Flow
Aa
Flow
Ba
Continued Qmb
Qc b
0.68231 0.30581 0.48517 0.67717 0.70886 0,33978 0.48517 0.69999 0.72998 0.37376 0.48517 0.73305 0.74650 0.40774 0.48517 0.74611 0.75936 0.44172 0.48517 0.75835 0.76941 0.47570 0.48517 0.76678 0.77731 0.50968 0.48517 0.77488 0.78359 0.54365 0.48517 0.77785 0.78864 0.57763 0.48517 0.78215 0.79275 0.61161 0.48517 0.79009 0.79612 0,64559 0.48517 0.79356 0,20589 0.06796 0.64690 0.21062 0.31214 0.10194 0.64690 0.31313 0.41985 0.13591 0.64690 0.41711 0.52817 0.16989 0.64690 0.51846 0.63272 0.20387 0.64690 0.62146 0.70688 0.23785 0.64690 0.70974 0.75689 0.27183 0.64690 0.75967 0.80137 0.30581 0.64690 0.79769 0.84181 0.33978 0.64690 0.86019 0.87800 0.37376 0.64690 0.88862 0.90974 0.40774 0.64690 0.91425 0.93702 0.44172 0.64690 0.93326 0.96007 0.47570 0.64690 0.95029 0.97934 0,50968 0.64690 0.96219 0.99533 0,54365 0.64690 0.97079 T = 373.15K; A = 0.1085mMgCl2; B = 0.03655mATP + 0.1460m N(CH3)4 § 0.10959 0,03398 0.48517 0.10135 0.22669 0,06796 0.48517 0.22598 0.34728 0.10194 0.48517 0,34929 0.46906 0.13591 0.48517 0.46104 0.57348 0.16989 0,48517 0.57609 0.63581 0.20387 0.48517 0.65467 0.69213 0.23785 0.48517 0.70501 0.74312 0.27183 0.48517 0.74711 0.78627 0.30581 0.48517 0.78623 0.81995 0.33978 0.48517 0.81528 0.84446 0.37376 0.48517 0.83806 0.86154 0.40774 0.48517 0.85919 0.87325 0.44172 0.48517 0.87107 0.88128 0,47570 0.48517 0.89187 0.88682 0.50968 0.48517 0.89765 0.89067 0.54365 0.48517 0.90409 0.89335 0.57763 0.48517 0.90178 0.89522 0.61161 0.48517 0.90277 0.89650 0.64559 0.48517 0.90425 0.22343 0.06796 0,64690 0.22334 0.34211 0.10194 0.64690 0.34384
999
Interaction of ADP and ATP with Mg ~+
Table III. Flow An
Flow Ba
Continued Qmb
0.13591 0.64690 0.45807 0,16989 0.64690 0,56999 0,20387 0.64690 0,67497 0.23785 0.64690 0.77451 0.27183 0.64690 0.84631 0.30581 0.64690 0.91317 0.33978 0,64690 0.96731 0.37376 0.64690 1.01270 0.40774 0.64690 1.04506 0.44172 0.64690 1.07593 0.47570 0.64690 1.10267 0.50968 0.64690 1.12479 0.54365 0.64690 1.14740 T = 398,15K; A = 0,1085mMgC12; B = 0.03863mATP 0.03398 0.48453 0.12845 0.06796 0.48453 0.27721 0.1019.4 0.48453 0.40433 0.13591 0.48453 0.54593 0.16989 0.48453 0.65025 0.20387 0.48453 0.74593 0.23785 0.48453 0.81548 0.27183 0.48453 0.86889 0.30581 0.48453 0.91598 0.33978 0.48453 0.95275 0.37376 0.48453 0.93544 0.40774 0.48453 0.95425 0.44172 0.48453 0.97821 0.47570 0.48453 1.01914 0.50968 0.48453 1.02929 0,54365 0.48453 1,04077 0.57763 0.48453 1.04892 0.61161 0.48453 1.06207 0.64559 0.48453 1.07837 0.06796 0.64604 0.29235 0.10194 0.64604 0.44775 0.13591 0.64604 0,60000 0.16989 0,64604 0.73661 0.20387 0.64604 0.86939 0.23785 0.64604 0,97821 0.27183 0.64604 1~06090 0.30581 0.64604 1.12163 0.33978 0.64604 1.15508 0.37376 0.64604 1.20533 0.40774 0.64604 1.25674 0.44172 0,64604 1.30832 0.47570 0.64604 1.34343 0.50968 0.64604 1.36689 0.54365 0.64604 1.38353 ~'bSee footnotes in Table II.
Qcb 0.46304 0.58500 0,70338 0.78723 0.84774 0.90461 0.95793 1.00632 1,04836 1.08325 1.11102 t.I3246 1.14872 0.1510m N(CH3)4+ 0.13390 0.27747 0.42623 0.57799 0.69831 0.76827 0,83443 0.89459 0.94387 0.97917 1,00183 1.01565 1.02404 1.02918 1.03235 1.03430 1.03545 1.03608 1.03637 0.27321 0.41899 0.56831 0.72004 0,86707 0,95533 1.02436 1,09103 1.15408 1.21082 1.25849 1.29554 1.32247 1.34127 1.35419
1000
Table IV.
Wang, Osearson, Izatt, Watt, and Larsen
Calorimetric Data for the Heats of Dilution of MgCI2 and of ATP/(CH3)4NOH
Flow A~
Flow B~ T=
323.15K;
A = 0.1085mMgC12; B = H20 -0.01534 -0.02301 -0.02660 -0.03101 -0.03917 -0.03346 - 0.03280 -0.03868 -0.03950 - 0.04276 -0.03688 -0.04537 -0.03607 -0.03688 -0.03476 T = 398.15K; A = 0.1085mMgC12; B = H20 0.06796 -0.04427 0.10194 0.65527 - 0.06125 0.13591 0.65527 -0.07157 0.16989 0.65527 -0.08638 0.20387 0.65527 -0.09819 0.23785 0.65527 - 0.10485 0.27183 0.65527 -0.11384 0.30581 0.65527 -0.11700 0.33978 0.65527 -0.12882 0.37376 0.65527 -0.13797 0.40774 0.65527 -0.14313 0.44172 0.65527 -0.15045 0.47570 0.65527 -0.15561 0.50968 0.65527 - 0.15911 0.54365 0.65527 -0.16427 T = 373.15 K; P = 1.52 MPa; A = H20; B ~- 0.03655m ATP + 0.1460m 0.06889 0.64862 -0.01782 0.10334 0.64862 -0.02674 0.13779 0.64862 -0.03532 0.17223 0.64862 -0.04027 0.20668 0.64862 -0.05116 0.24112 0.64862 - 0.04803 0.27557 0.64862 -0.05743 0.31002 0.64862 -0.06800 0.34446 0.64862 -0.07641 0.37891 0.64862 -0.08335 0.41336 0.64862 - 0.08912 0.44780 0.64862 -0.09242 0.48225 0.64862 - 0.10216 0.51670 0.64862 - 0.10992 0.55114 0.64862 -0.11074
0.06796 0.10194 0.13591 0.16989 0.20387 0.23785 0.27183 0.30581 0.33978 0.37376 0.40774 0.44172 0.47570 0.50968 0.54365
a,bSee footnotes in
Table II.
P = 1.52MPa; 0.65527 0.65527 0.65527 0.65527 0.65527 0.65527 0.65527 0.65527 0.65527 0.65527 0.65527 0.65527 0.65527 0.65527 0.65527 P = 1.52MPa; 0.65527
Qmb
Qcb
- 0.01401 -0.01888 - 0.02298 -0.02653 -0.02964 -0.03239 - 0.03485 -0.03708 -0.03909 - 0.04093 -0.04261 -0.04416 -0.04559 -0.04692 -0.04815 -0.04567 - 0.06145 -0.07476 -0.08623 -0.09627 -0.10516 -0.11310 -0.12026 -0.12674 -0.13264 -0.13805 -0.14302 - 0.14761
-0.15187 -0.15582 N(CH3)4 + -0.02026 -0.02938 -0.03791 -0.04591 -0.05344 - 0.06054 -0.06724 -0.07358 -0.07959 -0.08529 - 0.09072 -0.09588 - 0.10080 - 0.10550 -0.10998
Interaction of ADP and ATP with Mg 2+
Table V. t(~
log K
25 25 25 25 25 25 25 25 25 30 30 30 30 75 100
4.14 4.65 4.27 4.10 4.68
l5 25 75 100
1.0 1.7 2.10 2.29
27 75 100
0.806 0.79 0.79
3.17 3.28 3.50 4.39 3.695 3.66 3.48 4.89 5.29
1001
Thermodynamic Data for the Interaction of Mg +2 with ADP A/-F
AS~
AC~p
Method"
I
Medium
ADP 3- + Mg +2 = MgADP-, Reaction (1) sp 0.0 R4NXb pot 0.0 Na § 18.0 141.8 T 0.0 P~NX b 24.27 159 T 0.0 R4NXb 19.0 153 Ave 188 Est 0.2 R4NXb 15.1 111.3 T 0.t KNO3 17.53 121.6 C 0.1 NaC104 15.1 117.6 T 0.1 R4NXb sp 0.O NEM.HCI r 13.18 114.2 C 0.2 (CH3)4NC1 13.30 114.2 C 0.2 (CH3)4NCI 14.04 113 C 0.2 (CH3)4NCI 34.9 194 386 C 0.0 (CH3)4NOH 44.5 221 386 C 0.0 (CH3)4NOH MgADP- + Mg +~ :: Mg2ADW, Reaction (2) kin 0.1 KNO 3 pot 0.0 Na + 18.3 93 97 C 0.0 (CH3)gNOH 20.7 99 97 C 0.0 (CH3)4NOH MgADP- + MgADP- = (MgADP)~-, Reaction (9) NMR 0.1 NaNO3 -0.4 14 5 C 0.0 (CH3)4NOH --0.2 15 5 C 0.0 (CH3)4NOH
Refo
12,13 12 12,13 12,13 30 31 12,13 12 12 12 I2,13 13 13 d '/
12 12 d a 27 d d
aAve = average of existing values, Est = estimated, C = calorimetry, T = AH~ values determined from variation with temperature data, pot = potentiometry, sp = spectruphotometry, kin = kinetics, NMR = nuclear magnetic resonance. bTetraalkylammonium halide. CNEM = N-Ethylmorpholine. dThis study, the estimated uncertainties are -+0.01 in log K, ---0.8 kLmol -~ in AH~ +-3 J-mol-l-K-l in AS~ and +-16 J-mol-l-K -j in ACp~
the measured heat values. The expressions for AS~ and ACp~ as a function of temperature were derived from Eqs. (1 l) and (12) giving: AS~ = (c + 2.303 a)R + 2.303 cR lag T zXCp ~ = c R
(13)
(14)
Table VII gives the equations for log K, A/F, AS~ and ACp~for reactions (1), (2), (5), (6), (9), and (10) as functions of temperature. The estimated uncertainties for the parameters a, b, and c are also given in the footnote in Table VII. The heat of reaction calculated using these log K and AH ~ values, Qc, is
Wang, Osearson, Izatt, Watt, and Larsen
1002 Table VI. t(~
log K
20 25 25 25 25 25 25 25 25 25 25 25 25 25 26 30 30 30 37 50 75 100 125
3.65 6.06 5.87 5,70 5.83 5,72 6.22
25 25 25 25 37 50 75 100 125
2.61 2.5 2.72
27 50 75 100 125
0.602 0.53 0.46 0.41 0.36
4.22 2.24 3.343 4.03 4.22 4.63 4.62 6. I 1 4.693 4.67 4.73 6.17 6.61 7.12 7.67
1.69 2.82 3.15 3.50 3.84
Thermodynamic Data for the Interaction of Mg +2 with ATP
AH~
AS~
ACp
Methoda
1
Medium
ATP4- + Mg § = MgATP2-, Reaction (5) 101,0 T 0.12 NaC1 pot 0.0 Na § pot 0.0 Na § sp 0,0 RaNXb 21.3 182.8 T 0.0 R4NX b 20.1 176 T 0.0 23.0 196 Ave 126 Est 0.2 R~NXb 10.9 117.2 T 0.1 KNO3 14.2 90,4 T 0.1 KNO3 17.238 121.8 T 0.15 NaC1 18.08 138 C 0.1 NaC104 16.3 T 0.1 KNO3 13.8 134.9 T 0.1 R4NXb 18.8 l 51.5 T 0.2 (CH3)4NCI sp 0.C R4N?(h 18.70 151.5 C 0.2 (CH3)4NC1 18.66 151.0 C 0.2 (CH3)4NC1 18.3 149 C 0.2 (CHa)4NC1 31.6 216 507 C 0.0 (CHa)4NOH 44.3 254 507 C 0.0 (CH3)4NOH 56.9 289 507 C 0.0 (CH3)4NOH 69.6 322 507 C 0.0 (CH3)4NOH MgATP -2 + Mg +2 = Mg2ATE Reaction (6) pot 0.0 Na + sp 0.0 R4NXb 10.9 89 Ave 251 Est 0.2 R4NXb 7.2 161 C 0.2 (CH3)4NCI 26.2 135 210 C 0.0 (CH3)4NOH 31.5 151 210 C 0.0 (CH3)nNOH 36.7 165 210 C 0,0 (CH3)4NOH 42.0 179 210 C 0.0 (CH3)4NOH MgATP -2 + MgATP -2 = (MgATP) 4-, Reaction (10) NMR 0.1 NaNO3 -5.5 -7 4 C 0.0 (CH3)4NOH --5.4 --7 4 C 0.0 (CH3)4NOH -5.3 -6 4 C 0,0 (CH3)4NOH -5.2 -6 4 C 0.0 (CH3)4NOH 19.2
4. b, dSee footnotes in Table V.
Ref.
12 12 12 12 12 13 30 31 12,13 13 12,13 12 12 12 12 12 12,13 13 12 d d d d 12 12 30 31 12 d a d a 26 d a a a
Interaction of ADP and ATP with Mg z+ 0
0.2
0.4
1003
0.6
0
0.2
0.4
0.6
0,8 0
-0.1 -
-0.1
MgCl 2 + H 2 0
~
-0.2 -
- MgCI 2 + H 2 0
at 323.15 K
--0.2
at 398.15 K -0.3 -
O
-0.4 --0,5 0
Measured
O
Calculated
-
I
I
t
0.2
0.4
0.6
Flow
of
MgCI 2
--0.3
Measured
~
Calculated
t 0
0.2
solution
-0.4
~--"--T~ 0.4
0.6
--0.5 0.8
(gH20.min-1)
(a)
0
0.2
0.4
0.6
I
I
I
0.8
0-
0 -0.1
-0.2 - ATP/(CH3)4NOH + H 2 0
~- -0.2
at 373,15 K --~ -0.3 ;~ -0.4 -
-0.3 O
Measured
- -0.4
Calculated
-0.5 0
Flow
J 0.2
I 0.4
of H20
l ~ 0.6
(gH20.min"
-0.5 0.8
1)
(b) Fig. 2. Plot of heats of dilution, Qda,of (a) MgCI~_and (b) tetramethylammonium salt of ATP as a function of flow rate (gH2 O'min-t) at different temperatures.
1004
Wang, Osearson, lzatt, Watt, and Larsen
Table VIL
Equations for log K, A / F , AS~ and ACp~ for Reactions (1), (2), (5), (6), (9), and (10) as Functions of Temperature (298-398 K) at 1.52 MPa and I = 0 ~ (1)
(2)
(5)
(6)
(9)
(10)
A D P 3- + Mg 2- = M g A D P log K = - 1 2 8 . 1 8 4 + 5206/T + 46.473 log T A/-F = - 9 9 6 6 7 + 386.405 T AS~ = - 2 0 6 7 . 7 2 0 + 889.736 log T ACp ~ = 386.405 M g A D P - + M g 2§ = Mg2ADP § log K = - 2 9 . 8 4 0 + 807/T + l l . 6 5 3 log T A H ~ = - 1 5 4 4 8 + 96.888 T AS~ = - 4 7 4 . 4 1 0 + 223.094 log T ACe~ = 96.888 ATP 4- + Mg 2+ = M g A D P 2log K = - 1 6 8 . 1 2 2 + 6903/T + 60.943 log T AH~ = -- 132158 + 506.722 T AS~ = - 2 7 1 2 . 0 4 0 + 1166.780 log T ACp~ = 506.722 MgATP 2- + M g 2+ = Mg2ATP log K = - 6 7 . 2 6 5 + 2173/T + 25.245 log T AH ~ = --41606 + 209.906 T AS~ = - 1 0 7 7 . 7 4 0 + 483.329 log T ACp ~ = 209.906 M g A D P - + M g A D P - = (MgADP)22log K = - 1 . 0 3 3 + 109/T + 0.595 log T AH ~ = - 2 0 8 6 + 4.950 T AS~ = - 1 4 . 8 1 9 + 11.398 log T ACp ~ = 4.950 MgATP 2- + M g A T P 2- = (MgATP)2 nlog K = - 1 . 8 6 2 + 360/T + 0.508 log T A H ~ = --6889 + 4.223 T AS~ = - 3 1 . 4 2 1 + 9.724 log T ACp~ = 4.223
aThe estimated uncertainties in the parameters in the equation, log K = a + biT + c logT, are _+0.006 in a, ___2in b, and -+0.003 in c. (AH ~ in J-mol - l , AS~ in J - m o l - l - K -I and ACp ~ in J - m o l - t - K - t ) compared
to the measured
h e a t o f r e a c t i o n , Qm, i n F i g . 3 w h e r e t h e s e h e a t s a r e
p l o t t e d vs. t h e f l o w r a t e . T h e r e g r e s s i o n s t a n d a r d d e v i a t i o n s w a s c a l c u l a t e d f r o m
(aci-
am/) 2
$2 = i=l
(15) n --m
f o r e a c h s e t o f d a t a o b t a i n e d at t h e s a m e t e m p e r a t u r e flow rate setting, where n is the number number
of parameters
and the same nucleotide
of points in the data set, and m is the
to b e f i t t e d . T h e m a x i m u m
standard deviation
for the
Interaction of ADP and ATP with Mg 2+ 1,0 I
'
'
1005 s
I
l MgCI2 +ADP 0,8 l" at348.15K
~
'
i
i
l MgCI2 +ADP _ ~ at373.15K
0.4 asured 0.2
bY
o
sured
M~.~.rea-I-qr
o
M~.red
0.0
0.0
0.2
0.4
0,6
0.2
0.4
0,6
0.8
Flow of MgCI 2 solution (gH20.min q ) (a)
1.5
,
,
I
f
MgCI2 + ATP at 323.15 K
..=
"r'----r
=''-
MgCI2 + ATP at 348.15 K
LO
0.5
~ r
M
~
i
I
I
II
0 ~
M~ured Measured ~ Calculated f I
I
MgCI2 + ATP at 373.15 K
I
I
I
!
0 ~
red Measured Calculated |
-
MgCI2 + ATP . ~ at 3 9 8 ~
-
1.0
0.5
0 ~
0f 0,0
9 0.0
Measured Calculated
'
l
I
0.2
0,4
0.6
0.2
~
Measured
0
Measured Calcahted
0.4
0.6
0.8
Flow of MgCi2 solution (gH20.min "1) (b)
Fig. 3. Plot of heats of reaction, Q, of (a) ADP and (b) ATP with MgC12 as functions of MgCI 2 solution flow rate (gH20-min -l) at various temperatures, and ADP or ATP solution flow rates, o 30 ml-hr -~ ADP or ATP solution flow rate, 0 40 ml-hr-i ADP or ATP solution flow rate.
1006
Wang, Oscarson, Izatt, Watt, and Larsen
ADP data was found to be 0.045 J-min- ~and that for the ATP data was 0.044 J-min-i. These maximum standard deviations were found at 373.15 K for the ADP data and at 398.15 K for the ATP data. The values of m are 9 for both ADP and ATE Plots of AH~ as a function of temperature for reactions (1), (2), (5), (6), (9), and (10) are shown in Fig. 4. Plots of log K vs. temperature for these reactions are shown in Fig. 5 and plots of - T A S ~ vs. temperature are shown in Fig. 6. All complexation reactions (reactions (1), (2), (5), and (6)) are endothermic and have positive TAS~ values which increase with temperature. The AH~ values for all of these reactions also increase with temperature. The self-association reactions of MgADP- and MgATP 2- are both exothermic over the temperature range studied, and the A/F, AS~ and ACp ~ values for these reactions are all small and do not change significantly with temperature in comparison with those for the complexation reactions. Since both AH~ and AS~ values for the formation of complexes (reactions (1), (2), (5), and (6)) are positive and increase with temperature, the log Kvalues are dominated by AS~values, and these reactions are totally entropy-driven. The less favorable entropy changes for the self-association of ADP and unfavorable entropy changes for that of ATP are due to the involvement of fewer water molecules in these self-association reactions as will be discussed later. Three types of association reactions in aqueous solutions have been discussed by US. (25'32) These are charge reduction where a positive charge on one species is neutralized by a negative charge on the other, isocoulombic reaction where the number and signs of the charges for the reactants are the same as those for the products, and zwitterion f o r m a t i o n where the reaction type can resemble either charge reduction or isocoulombic depending on the degree of interaction between the charges. Reactions of the charge reduction type result in the release to the solvent of large numbers of water molecules and, consequently, have large ACp ~ values. The AH~ and AS~ values for reactions of this type increase with temperature. Reactions of the isocoulombic type release few water molecules and ACp ~ values are small. The A/-F and AS~ values for isocoulombic reactions do not change appreciably with temperature. The trends o f A H ~with temperature (ACp ~ vary among the reactions studied as seen in Fig. 4. Large ACp~ values for reactions (l) and (5) are to be expected since these reactions are of the charge reduction type as the Mg z+ binds to the negatively charged phosphates. The ACp~ value for reaction (6) (ACp ~ = 210 J-mol-l-K -1) is close to that of the interaction of Mg 2+ with HPO42- (ACp ~ = 251 J-mol-1-K-1(33)), indicating that binding of the second Mg e+ involves also the phosphate moiety of ATE The ACp ~ value for reaction (2) (ACp ~ = 97 J-mol-l-K -1) is comparable to that of the interaction of H + with HEPOg-(ACp~ = 105 J-mol-l-K-l(34)), in the same temperature range, indicating that reaction (2) involves neutralization of only one negative charge
o
300
[]
I
I
I
320
~Cp~
340
360
380
T(K)
400 280
Mg2++MgADP\=Mg2ADP+
I
MgADP-+MgADP'=(MgADP)22"
/
Mg2++ADp3"=MgADP-/D
I
300
I
O
I
I
/
|
j,~
320
340
A Cp ~=4
360
380
70
400
100
20
30
40
50
L 60
[
MgATp2-+MgATp2"=(MgATP)24" r L
M g2++ATI~'=MgATp2y
I
Fig, 4. Plot of AH~ values for reactions (1), (2), (5), (6), (9), and (10) as a function of temperature. Symbols at and above 323.15 K denote the results obtained from this study, all other points are obtained from literature data listed in Tables IV and V for ADP and . o l ATP. The solid lines are based on Eq, (12). Umts for ACp "areJ-mol- -K-1 .
-10~-280
0
10-
20-
30-
40-
50-
60-
70
+
%
2.
S"
0
275
2-
300
I
tara
I
I
I
325
350
I
tam
375
I
MgADP'+Mg~DP'=(M~DP)2 2"
Mg2++ADp3-=~
I
T(K)
400 280
I
300
[]
320
I
340
I
360
I
380
I
MgATp2-+MgATp2-=(MgATP)24-
400
it
-4
Fig. 5. Plot of log K values for reactions (1), (2), (5), (6), (9), and (10) as a function of temperature. Symbols at and above 323.15 K denote the results obtained from this study, all other points are taken from literature listed in Tables IV and V. The solid lines are based on Eq. (11).
0
6-
I
F
O
280
-120-
-$0'
-40
I
300
320
MgZ~ 340
360
380
m
m
300
320
340
360
380
400
rl
-120
-80
-40
MgATp2-+Mg2A-.T-P.(MgATP)24-
Mg 2 + + A T p 4 " = M g A ~
T(K)
400 280
-
ADP+
l. . . . .
MgADP'+MgADP-=(MgADP)22"
__L
~ g 2
m
I
Fig. 6. Plot of log - T A S ~ as functions of temperature for reactions (1), (2), (5), (6), (9), and (10). Symbols at and above 323.15 K denote the results obtained from this study, the points at 298.15 K are extrapolated based on Eqs. (1 l) and (13),
i
O
L
0 -
..._._.L___
to +
t~
g,
1010
Wang, Oscarson, lzatt, Watt, and Larsen
N
N
~ 1~~N N ~'- b & R
/ I,.H2 / /r
NH2
Fig. 7. Schematicdiagram for the head-to-tailstacking geometryof adenine nucleotides. R denotesthe sugar-phosphatemoiety.(28,35) on the phosphate groups by Mg 2+. Thus, the phosphate groups of ADP and ATP are involved in the formation of both the 1:1 and 2:1 (dimagnesium) complexes. The ACp ~ values for the reactions have the trend ( 5 ) > ( 1 ) > ( 6 ) > ( 2 ) which is attributed to the decreased number of negative charges on the reactant and product nucleotide or MgZ+-nucleotide complex species involved in these reactions. The magnitude of the AH ~and AS~values and their trends with temperature for the self-association reactions of MgADP 2- and MgATP 4- are also expected. The self-association of these nucleotides has been characterized as base-stacking. (28,29,35)The self-association occurs via vertical stacking of the base moieties, the base rings being parallel to each other with a head-to-tail stacking geometry (2s,35) as shown in Fig. 7. For a dimerization, the sugar-phosphate portions from the two monomers are apart from each other in the stacking. Since Mg 2+ ions are bound to the phosphate moieties in both MgADP 2- and MgATP 4-, phosphate groups and metal ion binding sites are not directly involved in the interaction as the self-association occurs. Therefore, there is no change in the net charge on the dimer (product) and on the two monomers (reactants). Thus, A/F, AS~ and ACp ~ values for these reactions are relatively small and do not change appreciably with temperature as expected for an isocoulombic reaction. Few values of AH ~ and AS~ for the self-association of ATP at 298.15 K are available. (28,29)Heyn and Bertz (2s) reported the AH ~ and AS~ values for the selfassociation of ATP in the presence of 1 M Tris/HC1 and 0.5 M MgC12. These values were obtained from a temperature variation study using ultraviolet absorption spectroscopy and circular dichroism. The sign of AH~ and AS~ obtained by these investigations is the same as that determined in our study. However, the magnitude of the A/-F and AS ~values (AH~ : - 2 1 . 3 kJ-tool -1, AS~ = - 5 4 . 4 J-mol-1 -K-1) is substantially more negative than those in the
Interaction of ADP and ATP with Mg 2+
1011
present study ( A H ~ = - 5 . 6 k J - m o l -~, AS ~ = - 7 . 4 J-tool -1 - K - l ) , as e x t r a p o lated to 298.15 K. The log K values given b y these authors are also m o r e positive than those g i v e n b y S c h e l l e r et al.
