Peptide maps of the myosin isoenzymes of Acanthamoeba castellanii.

Extracts of Acanthamoeba castellanii contain four myosin-like ATPases (Maruta, H., Gadasi, H., Collins, J.H., and Korn, E.D. (1979) J. Biol. Chem. 254, 3624-3630): double-headed Acanthamoeba myosin II and single-headed Acanthamoeba myosins IA, IB, and IC, which have heavy chains of 170,000, 130,000, 125,000, and 130,000 daltons, respectively, as well as different light chains. In the accompanying paper, evidence is presented that suggests that Acanthamoeba myosin IC is the same molecule as Acanthamoeba myosin IA plus a regulatory 20,000-dalton peptide. This conclusion is confirmed by the identity of the peptide maps obtained by limited proteolysis of the heavy chains of Acanthamoeba myosins IA and IC by Staphylococcus aureus V8 protease. However, peptide maps of the heavy chains of Acanthamoeba myosins IA, IB, and II obtained by limited proteolysis by the Staphylococcus protease and chymotrypsin and by chemical cleavage by cyanogen bromide and cyanylation have few, if any, peptides in common. From this evidence, and the enzymatic and subunit data in the accompanying paper, it is concluded that the three Acanthamoeba myosin isoenzymes, IA (IC), IB, and II, are products of different genes.