分岐鎖α-ケト酸脱水素酵素複合体に及ぼす脂肪酸および脂肪酸CoAの影響
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概要
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Branched-chain α-keto acid dehydrogenase complex (BCKADC) contains decarboxylase (E1), dihydrolipoyl transacylase (E2) and dihydrolipoamide dehydrogenase (E3) as catalytic components. The complex localizes in the mitochondrial matrix, and BCKADC plays an important role in regulating branched-chain amino acid levels. In this study, effect of fatty acyl-CoA on BCKADC activity was investigated in vitro. BCKADC was inhibited by acyl-CoA in μM order, and the inhibitor potency was increased with increasing chain length. Fatty acid also inhibited BCKADC depend on its hydrocarbon chain length, however concentration that gives rise to 50% inhibition was much higher than that of its acyl-CoA derivative. BCKADC reconstitution experiments showed that palmitoyl-CoA lowered both the binding affinity of E2 for E3 and the apparent maximum activity of BCKADC. Based on these results, it is concluded that long-chain fatty acyl-CoA binds to a certain site where the acyl-CoA exerts the inhibitory effect by affecting the interaction between E2 and E3, and the catalytic efficiency of BCKADC.