Actomyosin ATPase and Muscle Contraction

Abstract

This chapter discusses the actomyosin ATPase and muscle contration. The relatively simple organization of the functional unit of skeletal muscle, the sarcomere, lends itself to structural analysis and has led to the formulation of the sliding filament theory of muscle contraction. The energy for muscle contraction is provided by ATP and thus, it is possible to describe the crossbridge cycle in terms of the intermediate enzyme states of muscle ATPase. The problem of coupling of the hydrolysis of ATP to the production of mechanical force has been approached by structural, mechanical, and biochemical methods. The chapter focuses on the biochemical techniques used to investigate the kinetics of the cyclic interaction of myosin with actin and ATP. Transient and steady-state methods have provided a model for the crossbridge cycle in solution, but in general, less direct techniques must be used to investigate the crossbridge cycle in muscle. Applications of transient experiments of the rapid mixing type are limited, but single turnover experiments on rabbit myofibrils show that the equilibrium constant of ATP cleavage is similar to that obtained for the mechanically uncoupled acto-S1 ATPase. In principle, the most powerful methods of studying the crossbridge cycle in a muscle are of the relaxation type