Effects of diet and of alloxan-diabetes on the activity of branched-chain 2-oxo acid dehydrogenase complex and of activator protein in rat tissues

Abstract

The total activities (sum of active and inactive forms) of branched-chain 2-oxo acid dehydrogenase complex in tissues of normal rats fed on a standard diet were (unit/g wet wt.): liver, 0.82; kidney, 0.77; heart, 0.57; hindlimb skeletal muscles, 0.034. Total activity was decreased in liver by 9%- or 0%-casein diets and by 48 h starvation, but not by alloxan-diabetes. Total activities were unchanged in kidney and heart. The amount of active form of the complex (in unit/g wet wt. and as % of total) in tissues of normal rats fed on standard diet was: liver, 0.45, 55%; kidney, 0.55, 71%; heart, 0.03, 5%; skeletal muscle less than 0.007, less than 20% (below lower limit of assay). The concentration of the active form of the complex was decreased in liver and kidney, but not in heart, by low-protein diets, 48 h starvation and alloxan-diabetes. In heart muscle alloxan-diabetes increased the concentration of active complex. The concentration of activator protein (which activates phosphorylated complex without dephosphorylation) in liver and kidney was decreased by 70-90% by low-protein diets and 48 h starvation. Alloxan-diabetes decreased activator protein in liver, but not in kidney. Evidence is given that in tissues of rats fed on a normal diet approx. 70% of whole-body active branched chain complex is in the liver and that the major change in activity occasioned by low-protein diets is also in the liver.

Modulation of rat skeletal muscle branched-chain alpha-keto acid dehydrogenase in vivo. Effects of dietary protein and meal consumption.

“…As others have shown diet-mediated changes in BCKAD activities from liver, kidney, and heart (12,13,17,19,20), we first sought to optimize the assay for BCKAD isolated from muscles of rats fed diffiering levels of protein. Rats were meal-fed 0,25 (normal), or 50% (high) casein diets for 2 wk.…”

“…In contrast, < 20% of skeletal muscle BCKAD is in the active form (12,13,18,20,21). As skeletal muscle comprises -40% ofthe rat's body weight (22), changes in the phosphorylation state of muscle BCKAD could have profound effects on BCAA metabolism in vivo.…”

“…In view of the high BCAA aminotransferase and low BCKAD activity of muscles, it was proposed that muscle may primarily deaminate BCAA and release BCKA into the circulation for eventual oxidation by liver where BCKAD is found in abundance (12,13,24). Uncertainty about the role of muscle in BCAA metabolism has stemmed in part from the difficulty in measuring activities of BCKAD from solubilized muscle preparations (20,(25)(26)(27). Therefore, intact muscle mitochondria were used in most studies to assay BCKAD activity (13,18,23,26).…”

“…As skeletal muscle comprises -40% ofthe rat's body weight (22), changes in the phosphorylation state of muscle BCKAD could have profound effects on BCAA metabolism in vivo. However, efforts to detect changes in the activity state ofmuscle BCKAD in response to physiological manipulations have been largely unsuccessful (13,20,23). In view of the high BCAA aminotransferase and low BCKAD activity of muscles, it was proposed that muscle may primarily deaminate BCAA and release BCKA into the circulation for eventual oxidation by liver where BCKAD is found in abundance (12,13,24).…”

Effect of starvation and insulin in vivo on the activity of the pyruvate dehydrogenase complex in rat skeletal muscles

“…Mitochondria were prepared by differential centrifugation [16] and divided into two portions. One portion, used for the determination of the PDH complex activity at time of sacrifice (PDHa), was pelleted by centrifugation and immediately frozen in liquid nitrogen.…”