Branched-chain amino and keto acid metabolism in pancreatic islets.

The metabolism of L-leucine in pancreatic islets is reviewed. Regulatory sites may involve the transport and intracellular distribution of L-leucine, its transamination as modulated by the availability of 2-keto acids, the activity of branched-chain 2 keto acid dehydrogenase and the further catabolism of isovaleryl coenzyme A. Emphasis is also placed on the activation of glutamate dehydrogenase by L-leucine, its interference with the utilization of endogenous nutrients and the reciprocal effects of L-leucine and either L-glutamine or L-asparagine upon their respective metabolism. The relevance of L-leucine metabolism to its insulinotropic action is underlined.