Interaction of actin with N-ethylmaleimide modified heavy meromyosin in the presence and absence of adenosine triphosphate.

N-Ethylmaleimide modified heavy meromyosin in only 3-fold activated by actin rather than 200-fold as is normal heavy meromyosin (Silverman, R., Eisenberg, E., and Kielley, W.

The interaction of heavy meromyosin and subfragment 1 with actin. Physical measurements in the presence and absence of adenosine triphosphate.

Viscosity, turbidity, and laser-light fluctuation autocorrelations of acto-heavy merymyosin (HMM) and acto-subfragment 1 (S-1) solutions were measured under conditions where the actin-activated ATPase is close to its maximal value. The results were compared to similar data obtained in the absence of ATP where the actin and myosin fragments were completely domplexed, and in the presence of ATP but at 0.1 M KLC where the actin and HMM or S-1 were almost completely dissociated.

Heavy meromyosin: evidence for a refractory state unable to bind to actin in the presence of ATP.

The binding of actin to heavy meromyosin (HMM) in the presence of ATP was studied by analytical ultracentrifuge and ATPase studies. At 0 degrees C, at very low ionic strength, the double-reciprocal plot of HMM ATPase against actin concentration is linear. If one assumes that all of the HMM is bound to actin when the ATPase activity equals V(max), then, at an actin concentration where the actin-HMM ATPase is 85% of V(max), all but 15% of the HMM should be complexed with actin.