Observations on the role of sulfhydryl groups in the functioning of actomyosin

Abstract

The reaction of N-ethylamaleimide (NEM) with actomyosin causes the same pattern of activation and inhibition of ATPase activity at low KCl in the presence of Mg ++ as at high KCl in the presence of Ca ++. The reaction of enough NEM to cause maximal ATPase activation does not interfere with superprecipitation or with the ability of relaxing factor grana to prevent superprecipitation, but does decrease the tendency of actomyosin to dissolve at high ATP concentrations. Further reaction with NEM reverses the activation of ATPase activity and prevents superprecipitation. Superprecipitation can be completely inhibited before there is any net inhibition of ATPase activity. It is suggested that two —SH groups are involved in the functioning of myosin, and their roles in ATPase activity and in mechanochemical coupling are discussed.