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J. Biochem, 1988, Vol. 103, No. 5 750-754
© 1988 Japanese Biochemical Society

research-article

Elementary Steps of the Actin-Activated ATPase Reaction of Cardiac Muscle Myosin Subfragment-11

Makoto Miyata, Faculty of Science, Mitsukuni Yasui, Faculty of Science2, Toshiaki Arata, Faculty of Science and Akio Inoue, Faculty of Science

Department of Biology,Osaka University Toyonaka, Osaka 560

The rates of the elementary steps of the actomyosin ATPase reaction were measured using the myosin subfragment-1 of porcine left ventricular muscle. The results could be explained only by the two-route mechanism for actomyosin ATPase (Inoue, Shigekawa, & Tonomura (1973) J. Biochem. 74, 923-934), in which ATP is hydrolyzed via routes with or without accompanying dissociation of actomyosin. The dependence on the F-actin concentration of the rate of the acto-S-1 ATPase reaction in the steady state was measured in 5 mM KCl at 20°C. The maximal rate, Vmax, and the dissociation constant for F-actin of the ATPase, id, were 3.0 s–1 and 2.2 mg/ml, respectively. The Kd value was almost the same as that determined from the extent of binding of S-1 with F-actin during the ATPase reaction. The rate of recombination of the S-1-phosphate-ADP complex, , with F-actin, {nu}r, was lower than that of the ATPase reaction in the steady state. Thus, ATP is mainly hydrolyzed without accompanying dissociation of acto-S-1 into and F-actin. In the cardiac acto-S-1 ATPase reaction, the rate of the ATPase reaction in the steady state and that of recombination of with F-actin were about 1/5 those of the skeletal acto-S-1 ATPase reaction. Under more physiological conditions, i.e., 0.1 M KCl and 30C, the apparent second-order rate constant for the recombination of cardiac with F-actin (0.022 s–1 × (mg/ml)–1) was much smaller than that in the case of skeletal S-I (0.57 s–1× (mg/ml)–1). The ATP hydrolysis through the dissociation of actomyosin into +F-actin and their recombination may not be coupled with muscle contraction, since the velocity and the tension on cardiac muscle contraction do not differ so much from those of rabbit skeletal muscle.

1This work was supported by grants from the Ministry of Education, Science and Culture of Japan, the Ministry of Health and Welfare of Japan, and the Muscular Dystrophy Association, Inc.

2Present address: Department of Chemical Engineering, Muroran Institute of Technology, Muroran, Hokkaido 050.


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