INHIBITION OF ACTO-MYOSIN SUBFRAGMENT-1 ATPASE ACTIVITY BY PEPTIDES CORRESPONDING TO VARIOUS SEGMENTS OF THE 20-KDA DOMAIN OF MYOSIN HEAVY-CHAIN

As reported previously, the synthetic heptapeptide having the amino ac id sequence around the reactive Cys (SH1) of myosin heavy chain, IRICR KG-NH2, inhibited acto-myosin subfragment-1 (S-1) ATPase activity and half inhibition (K-1/2) was observed at a peptide concentration of 0.0 6 mM. The inhibitory ability of the peptide was found to be decreased to one-fifth by acetylation of its N-terminal alpha-amino group. A sim ilar effect of N-acetylation was observed with a nonapeptide, EGIRICRK G-NH2, and an undecapeptide, VLEGIRICRKG-NH2. These results indicate t hat N-terminal-free synthetic peptides do not act as proper analogs of the corresponding segment of S-1 heavy chain against F-actin. We isol ated a longer peptide extending from Thr(682) to Lys(709) in S-1 heavy chain, with two Cys residues corresponding to SH1 and SH2. This pepti de, having 28 residues (28peptide), inhibited acto-S-1 ATPase activity with a K-1/2 of 0.23 mM. A cosedimentation binding assay indicated th at the 28peptide completely dissociated acto-S-1 in the presence of AT P. This behavior is different from that observed with the N-terminal-f ree synthetic heptapeptide, and thus the 28peptide might be an analog of the corresponding segment. There is a possibility that the region c orresponding to the 28peptide in S-1 heavy chain may bind directly wit h F-actin and may be involved in determining the acto-S-1 link during the steady state of the acto-S-1 ATPase reaction.