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Branched-Chain -Keto Acid Dehydrogenase Complex in Rat Skeletal Muscle: Regulation of the Activity and Gene Expression by Nutrition and Physical Exercise¹

Yoshiharu Shimomura^*,2, Hisao Fujii, Masashige Suzuki, Taro Murakami^*, Noriaki Fujitsuka^* and Naoya Nakai³

^* Department of Bioscience, Nagoya Institute of Technology, Nagoya 466, Japan Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba 305, Japan

Branched-chain -keto acid dehydrogenase complex is the rate-limiting enzyme in the catabolism of branched-chain amino acids in skeletal muscle. It is suggested that activation of this enzyme in the muscle during exercise plays an important role in the increased oxidation of branched-chain amino acids in the muscle. Evidence suggests that branched-chain -keto acids, the substrates for the enzyme, regulate the activity state of the enzyme in the muscle during exercise through phosphorylation/dephosphorylation cycle of the enzyme protein. We propose a model for the mechanism of enzyme activation by exercise. In addition to this acute effect of exercise, we present evidence suggesting that exercise training modulates the enzyme activity and gene expression for the enzyme. Increases in the total activity as well as enzyme proteins by exercise training are suggested to be associated with mitochondrial biogenesis in the muscle.

KEY WORDS: • branched-chain -keto acid dehydrogenase • branched-chain amino acids • exercise

¹ Presented as part of the symposium "Alpha-Keto Acid Dehydrogenase Complexes: Nutrient Control, Gene Regulation and Genetic Defects" given at the Experimental Biology '94 meeting, Anaheim, CA, on April 27, 1994. This symposium was sponsored by the American Institute of Nutrition. Guest editors for this symposium were Mulchand S. Patel, State University of New York at Buffalo, Buffalo, NY and Robert A. Harris, Indiana University School of Medicine, Indianapolis, IN.

² To whom correspondence should be addressed: Department of Bioscience, Nagoya Institute of Technology, Gokiso-Cho, Showa-Ku, Nagoya 466, Japan.

³ Present address: Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya 464, Japan.