Takenori Yamada

A kinetic study of the energy storing enzyme-product complex in the hydrolysis of ATP by heavy meromyosin

Abstract The hydrolysis of ATP by heavy meromyosin was studied by means of the measurement of the development of enthalpy. The results were compared with the rate of change in the intensity of the ultraviolet difference spectrum of heavy meromyosin. It is shown that as far as the enthalpy change is concerned: (1) most of the excess energy associated with ATP does not directly dissipate into the solution during the rapid hydrolysis of ATP in the initial stage of the reaction but is stored in stable form in an enzyme-product complex, (2) the ultraviolet difference spectrum of heavy meromyosin is due specifically to the reaction via the enzyme-product complex, suggesting that a local conformation of heavy meromyosin is changed because of the excess energy stored in the complex, and (3) the complex dominantly exists during the steady splitting of ATP.

On the active streaming experiment of actomyosin solutions in glass microcapillaries

The active-streaming experiments of Oplatka et al. (Oplatka, A. and Tirosh, R. (1973) Biochim. Biophys. Acta 305, 684-688 and Oplatka, A. Gadasi, H., Tirosh, R. Lamed, Y., Muhlrad, A. and Liron, N. (1974) J. Mechanochem. Cell Motil. 2, 295-306) with actomyosin solution in a glass microcapillary is reexamined under various conditions with several kinds of reference material. It is found that vigorous streaming took place in the actomyosin solution as reported by Oplatka et al. However, streaming which is indistinguishable from that observed in the actomyosin solution in the presence of actomyosin ATPase activity also occurred, even when the ATPase activity was blocked. The streaming also cannot be confirmed as being active when using acto-heavy meromyosin solution. There is a possibility that the streaming experiment provides interesting information on the microscopic state of solutions which is not directly related to the chemo-mechanical conversion.