Investigation, by cross-linking, of conformational changes in F-actin during its interactions with myosin.

The hypothesis that the subunits of F-actin rotate during interactin with myosin and ATP has been tested by using the specific cross-linking reagent p-phenylene-N,N'-bis(maleimide) (PM). The insertion of cross-links between F-actin subunits does not change the ability of the F-actin to activate the ATPase of either myosin subfragment-1 (S-1) or heavy meormyosin, and its ability to superprecipitate with myosin is unimpaired. We conclude that large-scale rotations of actin subunits are not required for activity. The cross-linking of F-actin by PM is, however, inhibited in a noncooperative fashion by S-1 binding, suggesting that a small local change in actin structure may accompany the binding of S-1 or that S-1 sterically blocks the cross-linking by binding near the contact region between actin subunits.