Force generation and ATP hydrolysis in muscle contraction

Abstract

New data in favour of a simple and biochemically clear-cut model oftension generation in muscle, suggested earlier by the author (Kastrikin, 1978), are considered. The model is based on the formation of a sterically hindered, elastically bent actomyosin bond and its active straightening after the disappearance of the steric hindrance during MgATP hydrolysis. Compared with the two current mechanisms of force generation, the model of the conformational change of myosin head and Huxley-Simmons model, the bond straightening model seems to be more consistent with the main body of heterogeneous experimental data. This model is also in good agreement with a myosin-oxyphosphorane structure of the long-lived intermediate in MgATP hydrolysis (Young, McLick & Korman, 1974; Kastrikin, 1977, Kastrikin, 1978), but not with its myosin-product structure, which implies a six-step oxyphosphozane mechanism of myosin ATPase as an alternative to the seven-step Bagshaw-Trentham scheme. The bond straightening model predicts an increase in the angle of the myosin head attachment and a weakening of the actomyosin bond during an elastic phase of the stretch of rigor muscle fibres, with a tension decrease at elevated ionic strength or lowered temperature and no change in number of attached myosin heads.