The pressure, temperature and ion relations of myosin ATP-ase.

The kinetics of the hydrolysis of adenosine triphosphate (ATP) by the muscle protein myosin have received considerable attention in recent years, and several reviews have been devoted to this subject (Szent-Gyiirgyi, '55; Morales et al., '55; Buchthal et al., '56). The BTP-ase activity of myosin is modified by pressure (Laidler and Beardell, '55)' by calcium, magnesium and nucleotides (Blum, '55), and by calcium, pH and temperature (Green and Mommaerts, '54; Ouellet et al., '52). The effects of pressure, temperature and ions on ATP-ase activity have been interpreted in terms of a simple MichaelisMenten reaction scheme (Laidler and Beardell, '55 ; Green and Mommaerts, '54)' although other studies of the behavior of myosin have implicated a series of reactions (Mommaerts and Hanson, '56; Morales et al., '55; Watanabe et al., '53). In fact, Spicer ('55) has suggested that reversible denaturations may explain gelation phenomena in solutions of myosin B. Our interest in the problem arose from the observation that pressure reduces the isometric twitch tension of intact muscle at lower temperatures and increases it at higher ( Cattell and Edwards, '28). This has been ascribed to the effect of pres-