Regulation of branched chain amino acid catabolism in mammalian tissues: Characterization of the mitochondrial aminotransferase

Abstract

The branched chain aminotransferase (BCAT) catalyzes the first step in catabolism of the three essential branched chain amino acids (leucine, isoleucine, valine). The second step is irreversible oxidative decarboxylation of the transamination products, the branched chain α-keto acids, catalyzed by the branched chain α-keto acid dehydrogenase multienzyme complex. It is the tissue distribution of these two enzymes that is largely responsible for the unique metabolism of this group of amino acids among different organs and tissues [1]. Because branched chain α-keto acid dehydrogenase, which is the first rate-controlling step in branched chain amino acid catabolism, is a mitochondrial matrix enzyme, the subcellular distribution of BCAT in a tissue can influence branched chain amino acid oxidation. In the present study the role of the mitochondrial and cytosolic aminotransferase(S) in regulating branched chain amino acid oxidation is discussed. Molecular characteristics and purification of the mitochondrial aminotransferase from rat heart are presented, and the relationship of this enzyme to the brain cytosolic enzyme is described.