Branched Chain Amino Acid Metabolism and Maple Syrup Urine Disease Metabolic Pathway of Branched Chain Amino Acids (Leucine, Isoleucine, and Valine) Transamination of Branched Chain Amino Acid - The first step in the catabolism of branched-chain amino acids including leucine, isoleucine, and valine - Catalyzed by an enzyme branched-chain amino acid aminotransferase - Conversion of branched-chain amino acids to respective branched-chain keto acids - The amino group is transferred to alpha-ketoglutarate to form glutamate Decarboxylation of Branched Chain Keto Acids - Catalyzed by enzyme branch chain keto acid dehydrogenase complex (BCKDC) - BCKDC consists of four different subunits E1- α, E1-β, E2 & E3 - E1- α2 β2 tetramer is a thiamine pyrophosphate dependent decarboxylase encoded by BCKDHA & BCKDHB - E2 is dihydrolipoamide branched-chain transacylase encoded by DBT - E3 is a flavoprotein dihydrolipoamide dehydrogenase en...