Structure, function and assembly of mammalian branched-chain α-ketoacid dehydrogenase complex

Abstract

The mammalian branched-chain α-ketoacid dehydrogenase complex (BCKDC) catalyzes the oxidative decarboxylation of the branched-chain α-ketoacids derived from valine, leucine, and isoleucine. The mammalian BCKDC is a member of the α-ketoacid dehydrogenase complexes comprising pyruvate dehydrogenase (PDC), α-ketoglutarate dehydrogenase (KGDC) and BCKDC with similar structure and function (Reed et al., 1985; Yeaman, 1989). All three of these complexes are located in the mitochondrial matrix compartment and are associated with the inner membrane. BCKDC is a highly assembled macromolecular structure with an estimated molecular mass of 3 to 4 million daltons. BCKDC isolated from bovine kidney and liver has been shown to contain three catalytic components (Pettit et al., 1978; Heffelfmger et al., 1983): a branched-chain α-ketoacid decarboxylase (E1), a dihydrolipoyl transacylase (E2) and a dihydrolipoyl dehydrogenase (E3). The E3 components are shared by PDC, KGDC and BCKDC (Yeaman, 1989). BCKDC also contains two regulatory enzymes, a specific kinase (Shimomura et al., 1990; Lee et al., 1991) and a specific phosphatase (Damuni et al., 1984), which modulate the activity of BCKDC by reversible phosphorylation-dephosphorylation.