Step-like superprecipitation of actomyosin.

The superprecipitation of natural actomyosin prepared from rabbit skeletal muscle shows a step-like character under physiological conditions (KCl 0.14 M, ATP 0.001 M). Alkali metal cations applied in the same (0.14 M) concentration cause a delay according to the Hofmeister sequence, while in their presence the step-like character of superprecipitation is retained. Reduction of the Ca2+ concentration also causes a delay in the development of superprecipitation, but its step-like character is retained in this case, too. Increasing the Mg2+ concentration in the medium causes a delay or disappearance of superprecipitation and modifies it to occur in a single step. It is assumed that the actions studied exert, their effect in a combined way actin directly or indirectly on the interaction of actin and myosin.