The primary structure of the myosin head.

The sequence of the NH2-terminal 808 amino acid residues of chicken pectoralis muscle myosin head was determined. Three characteristic 20-, 23-, and 50-kDa fragments were isolated from a digest of myosin subfragment 1 (S1) by gel filtration on a Sephadex G-100 column in the presence of 5 M guanidine hydrochloride, followed by anion-exchange chromatography on a QAE-Sephadex A-50 column in the presence of 8 M urea. The fragments were sequenced completely by conventional methods. Peptides overlapping the 23- and 50-kDa fragments and also overlapping the 50- and 20-kDa fragments were obtained by cleaving S1 with cyanogen bromide. Comparison of the 23-kDa and 50-kDa sequences with that of the overlapping peptide indicated that no additional amino acid exists between the 23- and 50-kDa fragments and that 5 amino acids exist between the 50- and 20-kDa fragments of S1. Methylated amino acid residues were found at four positions: epsilon-N-monomethyllysine at position 35, epsilon-N-trimethyllysine residues at 130 and 550, and 3-N-methylhistidine at 754.