The alpha-ketoisocaproate catabolism in human and rat livers

Catabolism of alpha-ketoisocaproate in liver is mediated by cytosolic alpha -ketoisocaproate dioxygenase (KICD) and mitochondrial branched-chain alpha- keto acid dehydrogenase complex (BCKDC). The latter is believed to be invol ved in the main pathway of the KIC catabolism. In the present study, we mea sured the activities of KICD and BCKDC in human and rat livers. The KICD ac tivity in human liver was 0.9 mU/g tissue, which was 14.2% of the total act ivity of BCKDC, and that in rat liver was 4.2 mU/g tissue, which was only 1 .0% of the total activity, suggesting that KICD in human Liver plays a rela tively important role in the alpha-ketoisocaproate catabolism. The KICD act ivity in human liver was significantly increased by cirrhosis. In rat Liver , the enzyme activity was markedly increased by physical training and strep tozotocin-induced diabetes, but not by feeding of a diet rich in branched-c hain amino acids, although BCKDC activity was increased by feeding of the d iet, (C) 2000 Academic Press.