Conformational changes of S-1 related to its dissociation from actin.

The peptide pattern obtained after proteolysis of S-1 with trypsin was different in the absence or presence of anions. The affinity of tryptic and undigested S-1 for anions (CN-, SCN- or HCO3-) was different, as reflected by the altered values of Ki or Ka obtained from ATPase activity measurements. Anions CN-, SCN-, HCO3-, or PPi induced dissociation of actomyosin when added to acto-S-1 or acto-heavy-meromyosin. Among nucleoside di- and triphosphates, only triphosphates were effective with regard to the dissociation. The results suggest the existence of a regulatory site of cationic nature on S-1, which might be involved in the dissociation of actin from myosin.