Activation of Hepatic Branched-Chain α-Ketoacid Dehydrogenase Complex by Vitamin D Deficiency in Rats

Branched-chain α-ketoacid dehydrogenase (BCKDH) complex is a rate-limiting enzyme in branched-chain amino acid catabolism and is subject to inactivation via phosphorylation by BCKDH kinase (BDK). In the present study, we examined the effects of vitamin D-deficiency on hepatic BCKDH and BDK activities in rats. Rats fed a vitamin D-deficient diet long-term showed a slight but significant decrease in plasma Ca concentration, which was associated with an elevation of BCKDH activity and a decrease in BDK activity. These results suggest that vitamin D deficiency promotes BCAA catabolism via BCKDH activation, which resulted from BDK suppression. It is proposed that Ca²⁺-dependent BDK inhibition by thiamine pyrophosphate may be involved in the BDK suppression.