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J. Biochem, 1988, Vol. 104, No. 4 550-556
© 1988 Japanese Biochemical Society

research-article

Oxygen Exchange during the Acto-Subfragment-1 ATPase Reaction: Evidence for the Two-Route Mechanism of the Actomyosin ATPase Reaction1

Mitsukuni Yasui*,2, Masato Ohe**, Akihiko Kajita**, Toshiaki Arata* and Akio Inoue*,3

*Department of Biology, Faculty of Science, Osaka University Toyonaka, Osaka 560
**Department of Biochemistry, Dokkyo University, School of Medicine Mibu, Tochigi 321-02

2To whom correspondence should be addressed

The oxygen exchange occurring during the acto-S-1 ATPase reaction was analyzed based on the distribution of 18O-labeled species of P1 using [{gamma}–18O]ATP as a substrate. Evidence was found for the two-route mechanism in which ATP is hydrolyzed via the dissociation of acto-S-1 into F-actin and the S-1-phosphate.ADP complex, S-1PADP and their recombination, and also hydrolyzed without the dissociation of acto-S-1 (Inoue, A., Shigekawa, M., & Tonomura, Y. (1973) J. Biochem. 74, 923–934; Inoue, A., Ikebe, M., & Tonomura, Y. (1980) J. Biochem. 88, 1663–1677). When ATP was mainly hydrolyzed without the dissociation of acto-S-1, the extent of oxygen exchange was low. When ATP was hydrolyzed by both routes, the distribution of product P1 with 3, 2, 1, and 0 18O atoms showed a mixture resulting from low and high oxygen exchange. The rate of ATPase without the dissociation of acto-S-1 can be estimated from the rate of the overall reaction ({nu}), the rate of recombination of S-1PADP with F-actin ({nu}r), and the extent of dissociation of acto-S-1 ({alpha}). The distribution of the P1 species measured was almost equal to that calculated from the ratio of ATP hydrolysis via the two pathways as {alpha}{nu}r and {nu}{alpha}{nu}r, respectively. This result indicates that the rates of the dissociation of acto-into and F-actin and their recombination are much lower than the rate of decomposition of the acto-complex into acto-S-1 + ADP + P1.

1This investigation 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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