Motion-Controlled ATP Hydrolysis in Reconstituted Streaming from Rabbit Skeletal Muscle

Abstract

SummaryRecently, we described an apparatus termed “stream cell” in which circular streaming could be induced by the interaction of heavy-meromyosin with F-actin purified from rabbit skeletal muscle. Since the streaming was observed only under conditions similar to those during muscle contraction, we concluded that it was active and driven by ATPase. The most typical feature of this system was that the acto-heavymeromyosin ATPase activity was uniquely determined by the macroscopic streaming velocity. In order to explain the chemomechanical conversion observed in the active streaming, dynamic cooperativity among force generators was required. Dynamic cooperativity during chemo-mechanical conversion implies that myosin crossbridges do not always act as independent force generators. For further study of the energy conversion in actomyosin system, we report here a new streaming system “grid stream system”, in which not only the velocity but also the direction of streaming can be controlled externally. Upon increasing the positive streaming velocity, the ATPase activity first increases and then decreases. On the contrary, at negative streaming velocities, corresponding to lengthening, the ATPase activity is not affected. The molecular mechanism of energy conversion will be discussed in relation to those observations.