Differences in chemical structure around the reactive lysine residues in the burst and the nonburst heads of skeletal muscle myosin.

Our laboratory has presented strong evidence for the nonidentical two-headed structure of skeletal muscle myosin. We previously showed that each of the two kinds of heads, i.e., the burst head, which forms the myosin-P-ADP complex, and the nonburst head, which forms the myosin-ATP complex upon reaction with ATP, contains 1 mol of reactive lysine residue per mol which is modified rapidly with TNBS. We also found that in the presence of PPi only the reactive lysine residue in the burst head is modified with TNBS. Utilizing this phenomenon, we presented evidence [(1981) J. Biochem. 89, 831-839] indicating that the chemical structures around the reactive lysine residues in the burst and the nonburst head are different. In this study, we determined the amino acid sequence around the reactive lysine residues to demonstrate the nonidentical chemical structure of the two heads of skeletal muscle myosin. We found that the sequence around the reactive lysine residue in the burst head was ....Pro-Met-Asn-Pro-Pro-Lys-Tyr.... and the sequence in the nonburst head was ....Ser-Met-Asn-Pro-Pro-Lys-Tyr..... Thus, a proline residue located ner the reactive lysine residue in the burst head was found to be replaced by a serine residue in the nonburst head.