DECARBOXYLATION STUDIES OF GLUTAMATE, GLUTAMINE, AND ASPARTATE FROM BRAIN LABELLED WITH [1‐14C] ACETATE, l ‐[U‐14C]‐ASPARTATE, AND l ‐[U‐14C]GLUTAMATE

Studies in vivo and in vitro of the distribution of label in C‐1 of glutamate and glutamine and C‐4 of aspartate in the free amino acids of brain were carried out. [1‐14C]‐Acetate was used both in vivo and in vitro and l‐[U‐14C]aspartate and l‐[U‐14C]glutamate were used in vitro. The results obtained with labelled acetate and aspartate suggest that CO2 and a 3‐carbon acid may exchange at different rates on a COa‐fixing enzyme. The apparent cycling times of both glutamate and glutamine show fast components measured in minutes and slow components measured in hours. With [1‐14C]acetate in vitro glutamine is more rapidly labelled in C‐1 than is glutamate at early time points; the curves cross over at about 7 min. The results support and extend the concept of metabolic compartmentation of amino acid metabolism in brain.