13N as a tracer for studying glutamate metabolism.

摘要

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 (13)N (t(1/2) 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 t(1/2) for conversion of portal vein ammonia to urea in the rat liver is approximately 10-11s, 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