Estimates of Force and Time of Actomyosin Interaction in an Active Muscle and of the Number Interacting at Any One Time

It is now generally accepted that muscle generates force and does work because of the hydrolysis of ATP at the hydrolytic site on myosin. Moreover it is known that this hydrolytic event itself is extremely rapid and that in isolated myosin or relaxed, glycerol-extracted muscle the ADP-myosin complex so formed is relatively stable (Lymn and Taylor, 1971; Marston and Tregear, 1972). However the subsequent course of events remains unclear; there is not even sure evidence that myosin attaches to actin during muscular contraction, although various changes in the X-ray diffraction pattern indicate that it does (Huxley, 1967; Armitage et al., this volume) and it certainly does so in the absence of ATP (Reedy, 1968). In this work we have assumed that actomyosin interaction occurs during contraction and that this causes the force and work observed. On this basis we have sought to assess the characteristics of the interaction.