Ann. Rev. Physiol. 1987. 49:637-54
This chapter reviews some recent estimates of specific elementary rate constants of the actomyosin ATPase in muscle fibers. These values are compared to the corresponding rate constants obtained with myosin and actomyosin in solution to determine whether or not the packing of the proteins into the normal filament lattice influences the reaction rates and to determine which elementary reactions are modulated by mechanical stress and strain on the proteins. A biochemical scheme for the actomyosin ATPase in solution is given in the General Introduction to this Special Topic section and is hereafter referred to as Scheme 1. Reasons to expect important differences between the kinetics of the actomyosin ATPase in solution and in fibers are discussed in the General Introduction. The reaction rates in fibers for steps in the pathway are compared to the overall ATPase activity. Reaction steps that are fast in isometric contracting conditions are unlikely to be rate-limiting control points required to explain increased energy liberation during shortening. The discussion here is limited almost exclusively to glycerol-extracted skeletal muscle fibers from rabbit psoas muscle because the most detailed comparison of the biochemistry and physiology has been performed on that system. In addition to the remainder of this Special Topic section, related reviews by Eisenberg & Hill (21) and Hibberd & Trentham (44) have recently appeared.