Effect of Tropomyosin on the Calcium-activated Adenosine Triphosphatase of Actomyosin

Abstract

IT is well known that the Mg⁺⁺-activated ATPase of actomyosin extracted as the complex from muscle, “natural” actomyosin, is inhibited by low concentrations of ethylene dioxybis (ethyleneamino) tetra-acetic acid (EGTA), a property not possessed by actomyosin prepared from separately purified actin and myosin¹. During a study of the factors responsible for the differences in enzyme behaviour of these two preparations a simple procedure has been developed which enables “natural” actomyosin to be readily converted to so-called “desensitized” actomyosin, the behaviour of which resembles actomyosin prepared from the independently purified actin and myosin in that its Mg⁺⁺-activated ATPase is no longer sensitive to EGTA^2,3. It was noted that in addition to the difference in sensitivity to EGTA of the two preparations the specific ATPase activity of “natural” actomyosin in the presence of Ca++ was 30–50 per cent of that of the desensitized actomyosin.