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J. Biochem, 1982, Vol. 91, No. 1 157-166
© 1982 Japanese Biochemical Society

research-article

Possible Role of ATP in Dimerization of Myosin Molecules from Chicken Gizzard Muscle1

Hirofumi ONISHI

Department of Chemistry, Faculty of Science, Tokyo Institute of Technology Meguro-ku, Tokyo 152

The mechanism of ATP hydrolysis by chicken gizzard myosin was investigated at 0.2 M KCl where dimerization of myosin occurs as well as at 0.3 M KCl where dimerization of myosin does not occur.

  1. The ATP-induced difference spectrum of UV absorption of gizzard myosin obtained in 0.2 M KCl was identical, not only in size but also in shape, with that obtained in 0.3 M KCl. Therefore, we propose that the ATP-induced conformation of myosin is the same in both its dimeric form and its monomeric form.
  2. According to a kinetic study, the rate of the ATP-induced enhancement in myosin fluorescence obtained in 0.2 M KCl was approximately equal to that ob tained in 0.3 M KCl. On the other hand, the rate of the subsequent decay of the ATP-induced fluorescence enhancement was much lower in 0.2 M KCl than in 0.3 M KCl.
  3. The rate of the initial burst of ATP hydrolysis obtained in 0.2 M KCl was approximately equal to that obtained in 0.3 M KCl. On the other hand, the rate of ATP hydrolysis in the steady state was much lower in 0.2 M KCl than in 0.3 M KCl. Based on the results described above, we propose (a) that Formula can be degraded only via monomers of Formula and (b) that the concentration of monomers of Formula in the steady state of ATP hydrolysis is decreased as a consequence of the dimerization of Formula in 0.2 M KCl. (** indicates the conformational change of myosin with the spectrum change of UV absorption.)

We also found that upon addition of AMPPNP, a dimeric form of gizzard myosin was produced in 0.2 M KCl. Therefore, ATP hydrolysis appears not to be required for the formation of myosin dimers.

1 This study was presented at the Japan-U.S. Seminar "Structure and function of myosin" in Sapporo on July 25th, 1980.


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