Leucine aminotransferase (EC 2.6.1.6) and
2-oxoisocaproate dehydrogenase (EC 1.2.4.3) were studied in rat cerebral cortex, cerebellum, brain stem, liver, and muscle in normal and animals starved for 48 hours. In the brain,
leucine aminotransferase,
valine aminotransferase, and
2-oxoisocaproate dehydrogenase showed a significant increase in
starvation only in cerebellum while there was increase in
2-oxoisocaproate dehydrogenase in cerebral cortex only. A significantly high increase in the activity of
2-oxoisocaproate dehydrogenase was observed in muscle in
starvation. A significant decrease in the activity of
leucine aminotransferase was observed in liver in
starvation. The increase in the activity of
2-oxoisocaproate dehydrogenase in muscle and a decrease in the activity of
leucine aminotransferase in liver in
starvation indicate that the
leucine is predominantly metabolized in extra hepatic tissues particularly in muscle. As a result of intraperitoneal administration of 2 ml of
leucine (5 mM), a significant increase in
2-oxoisocaproate dehydrogenase occurred in cerebral cortex, liver, and muscle while a profound increase in the activity of
glutamate dehydrogenase (EC 1.4.1.2) was observed in all the brain regions and liver under these conditions. A significant increase in the content of
glutamic acid,
alanine, and
GABA was observed in all the three regions of the brain after the administration of
leucine. A significant increase in the content of
glutamine was observed only in the cerebellum and cerebral cortex after
leucine administration. These results indicate that
leucine in brain might contribute to the formation of
glutamate, not only by transamination, but also by promoting
glutamate dehydrogenase activity. Thus, there is a change in the metabolism of
glutamate family of
amino acids and energy depletion. These results are discussed in relation to the brain function.