• BMB Reports
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• v.28 no.1
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• pp.12-16
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• 1995

The branched-chain ${\alpha}$-keto acid dehydrogenase (BCKAD) complex is a rate limiting enzyme which catalyzes the oxidative decarboxylation of branched-chain ${\alpha}$-keto acids. Numerous studies have suggested that BCKAD is subject to covalent modification in vitro via phosphorylation and dephosphorylation, which are catalyzed by a specific kinase and phosphatase, respectively. The biggest difficulty in the assay of BCKAD activity is to arrest the interconversion between the active and inactive forms. BCKAD activity was determined from fresh rat heart and liver tissues using homogenizing and assay buffers containing inhibitors of phosphatase and kinase. The results suggest that a radiochemical assay using ${\alpha}$-keto[1-$^{14}C$]-isovalerate as a substrate for the enzyme can be applied as a reliable method to determine in vitro enzyme activity with arrested interconversion between the active and inactive forms of the BCKAD complex.

• Journal of Nutrition and Health
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• v.27 no.9
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• pp.892-900
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• 1994

A variety of important roles for branched-chain amino acids in metabolic regulation has been suggested. Branched-chain $\alpha$-keto acid dehydrogenase(BCKAD) complex is a rate limiting enzyme in branched-chain amino acid metabolism. The purpose of this study was to examine the effects of exercise on the activity and activity state of branched-chain $\alpha$-keto acid dehydrogenase in rat hert and liver thssues. Forty-eight Sprague-Dawley rats were assigned into three experimental groups : sedentary control, exercised, or exercised-rested. Submaximal exercise(running) for two hours significantly increased basal activity without a change in total activity in both tissues, with a concomitiant increase in activity state of the enzyme complex. At 10 min post-exercise, heart enzyme activity significantly decreased, though not to the control level, while liver enzyme activity remained unchanged. These data suggested that the exercise-induced increase in branched-chain $\alpha$-keto acid decarboxylation in rat tissues may not be the result of enzyme synthesis, but rather is due to increased activity of the BCKAD.