Preparation of frog myosin. Isolation and characterization of the light chains.

Frog myosin can be prepared with a good yield by precipitation of a high ionic strength extract between I 0.20 and 0.05 or by ammonium sulphate fractionation of actomyosin in the presence of Mg-ATP. Two alkali light chains, LC1 and LC3, along with one DTNB light chain LC2 have been isolated by chromatography on ion exchange cellulose after urea dissociation. A supplementary light chain LC1d present in variable amounts from one preparation to the other corresponds to a proteolysis product of LC1. Their stoichiometry, molecular weight, amino acid composition, isoelectric point and peptide map have been determined. Their general proportions and structural properties show many similarities with rabbit skeletal muscle light chains. Amino acid compositions and peptide maps confirm that the additional band LC1d comes from a proteolytic degradation affecting the N-terminal part of LC1.