The Primary Structure of Skeletal Muscle Myosin Heavy Chain: I. Sequence of the Amino-Terminal 23 kDa Fragment

Abstract

Subfragment-1 was prepared from adult chicken pectoralis myosin by limited digestion with α-chymotrypsin, and an amino-terminal 23 kDa fragment of the heavy chain was obtained by digesting the subfragment-1 with trypsin. The 205-residue sequence of the fragment was determined by sequencing its cyanogen bromide, tryptic, and chymotryptic peptides. The amino-terminal α-amino group of the fragment was acetylated, and two methylated lysines; ε-N-monomethyllysine and ε-N -trimethylly sine were recognized at the 35 th and 130th positions, respectively, as in rabbit skeletal myosin. Comparing the 205-residue sequence of the skeletal myosin with those of cardiac, and gizzard myosins from chicken, considerable differences are recognized, especially in the amino-terminal region, but strong homologies are observed around the reactive lysine residue, around the ε-N-trimethyllysine residue, and around the consensus sequence of GXXGXGKT for nucleotide-binding proteins. On the other hand, only 12 amino acid substitutions are recognized between adult and embryonic skeletal myosins, allowing for the post-translational methylation.