NIH Public Access Author Manuscript Neurochem Int. Author manuscript; available in PMC 2012 September 1.
NIH-PA Author Manuscript
Published in final edited form as: Neurochem Int. 2011 September ; 59(4): 456–464. doi:10.1016/j.neuint.2010.11.011.
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N as a tracer for studying glutamate metabolism
Arthur J. L. Cooper* Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY 10595
Abstract
NIH-PA Author Manuscript
This mini-review summarizes studies my associates and I carried out that are relevant to the topic of the present volume [i.e. glutamate dehydrogenase (GDH)] using radioactive 13N (t½ 9.96 min) as a biological tracer. These studies revealed the previously unrecognized rapidity with which nitrogen is exchanged among certain metabolites in vivo. For example, our work demonstrated that a) the t½ for conversion of portal vein ammonia to urea in the rat liver is ~10–11 sec, despite the need for five enzyme-catalyzed steps and two mitochondrial transport steps, b) the residence time for ammonia in the blood of anesthetized rats is ≤7–8 sec, c) the t½ for incorporation of bloodborne ammonia into glutamine in the normal rat brain is
