Regulation of branched-chain α-ketoacid dehydrogenase kinase

Abstract

Isolated rabbit liver branched-chain α-ketoacid dehydrogenase was inhibited in a mixed manner relative to ATP by α-ketoisocaproate, α-keto-β-methylvalerate, α-ketoisovalerate, α-ketocaproate, α-ketovalerate, and α-chloroisocaproate with I 40 values m m), respectively, of 0.065, 0.49, 2.5, 0.2, 0.5, and 0.08. The concentration (m m) of α-ketoisocaproate, α-keto-β-methylvalerate, and α-ketoisovalerate needed to activate branched-chain α-ketoacid dehydrogenase in the perfused rat heart to 50% of total activity was 0.07, 0.10, and 0.25, respectively. Isolated branched-chain α-ketoacid dehydrogenase kinase was inhibited (I 40 values, m m) by octanoate (0.5), acetoacetyl-CoA (0.01), methylmalonyl-CoA (0.2), NADP + (1.5), and heparin (12 μg/ml). The kinase activity, in the presence or absence of ADP, was inhibited approximately 30% by 0.1 m m isobutyryl-CoA, isovaleryl-CoA, and malonyl-CoA, while not affected by NAD + and NADH (1 m m), CoA, acetyl-CoA, methylcrotonyl-CoA, crotonyl-CoA, β-hydroxy-β-methyl-glutaryl-CoA, octanoyl-CoA, succinyl-CoA, and propionyl-CoA (0.1 m m). The following compounds at 2 m m also did not inhibit branched-chain α-ketoacid dehydrogenase kinase; acetate, propionate, β-hydroxybutyrate, lactate, acetoacetate, malonate, α-ketomalonate, succinate, citrate, oxaloacetate, FAD, and NADPH. These findings help explain the unique effects of Leu compared with Val and Ile on branched-chain amino acid metabolism and the differences between control of the kinases associated with pyruvate dehydrogenase and branched-chain α-ketoacid dehydrogenase.