Control of the activity of branched-chain alpha-keto acid dehydrogenase complex in primary cultured rat hepatocytes.

When isolated rat hepatocytes were cultured in the medium containing 0.5 mM clofibrate (dissolved in ethanol) for 6 hours, the activity of branched-chain alpha-keto acid dehydrogenase (BCKADH) complex in the cells increased to more than two times that of control cells. Immunochemical determination with an anti-BCKADH IgG revealed that the activity increase occurred without increase in the enzyme amount. On the contrary, BCKADH activity in control cells (cultured in the presence 0.4% ethanol) decreased to two-third the initial activity at the end of 6-hour incubation whereas the activities of other enzymes tested were practically unaltered either in control or in clofibrate-treated cells. When the control cell extract was incubated with rat liver protein phosphatase, the BCKADH activity increased near to that of clofibrate-treated cells, but the same treatment of clofibrate-treated cell extract produced practically no increase in the activity. These observations indicate that clofibrate addition brought about the increase of BCKADH activity through activation-inactivation mechanism based on dephosphorylation-phosphorylation, and that this mechanism might function on liver BCKADH complex in vivo as a short term control of the activity in some conditions.