Native tropomyosin: Effect on the interaction of actin with heavy meromyosin and subfragment-1

Abstract

In the absence of Ca ++, native tropomyosin markedly inhibits the acto-subfragment-1 ATPase as well as the acto-heavy meromyosin ATPase despite the fact that subfragment-1, in contrast to heavy meromyosin, has only a single site for ATP. Double reciprocal plots of acto-heavy meromyosin ATPase vs. actin concentration both in the presence and absence of native tropomyosin, show that the native tropomyosin has little effect on the acto-HMM-ATPase but acts mainly by affecting the binding of actin to the HMM-ATP complex.