Identification of atrial-specific myosin heavy chain in cardiac muscle of adult chickens

The partial amino acid sequence of subfragment-1 of adult chicken atrial myosin was determined by direct protein sequencing. Subfragment-1 was prepared by limited digestion of adult chicken atrial myosin with alpha-chymotrypsin. Ten peptides were then obtained by cleaving this subfragment with cyanogen bromide. The amino acid composition and amino acid sequence of the obtained peptides were subsequently determined, By sequence comparison with the corresponding region of adult chicken ventricular myosin, three peptides, with differing sequences that corresponded to the same position in subfragment-1, were detected. This indicates that at least three isoforms of atrial myosin exist in adult chicken atrial muscle. One of the three peptides was identical to ventricular subfragment-1 while the remaining two peptides were markedly different. Furthermore, four of these ten peptides were completely different from ventricular subfragment-1. These four peptides were presumed to be fragments of atrial-specific myosin heavy chain protein, Results suggest the expression of at least two species of atrial-specific myosin heavy chain in the atrial muscle of adult chickens.