Amino acid sequence of a myosin fragment that contains SH-1, SH-2, and Ntau-methylhistidine.

A peptide having 92 amino acid residues and a calculated molecular weight of 10,478 was isolated from a cyanogen bromide digest of rabbit skeletal muscle myosin. It contained both proline and Ntau-methylhistidine, indicating that it arose from the portion of the heavy chain that folds to form most of the globular head of the myosin molecule. The amino acid sequence of the peptide included the two sulfhydryl groups whose alkylation modifies myosin's catalytic properties: SH-2 at position 11 in the peptide, and SH-1 at position 21. This proximity in the sequence means that SH-1 and SH-2 must be relatively close together in myosin, and several lines of evidence suggest that this region is near the catalytic or actin binding site(s) of myosin.