EVIDENCE FOR INVOLVEMENT OF A 12-RESIDUE PEPTIDE SEGMENT OF THE HEAVY-CHAIN IN THE NECK REGION OF SMOOTH-MUSCLE MYOSIN IN FORMATION OF THE 10S CONFORMATION

Two synthetic peptides having amino acid sequences of the heavy chain segments in the neck region of porcine aorta smooth muscle myosin were used to study the formation of the 10S folded conformation, These pep tides, MHC821-835 and MHC835-846, correspond to residues 821-835 and 8 35-846, respectively, of the chicken gizzard myosin heavy chain, The e ffects of these peptides on the filament formation of porcine aorta sm ooth muscle myosin were examined, The filamentous myosin fraction incr eased on the addition of MHC835-846 at NaCl concentrations lower than 0.25 M for both dephosphorylated and phosphorylated myosin, while the filament formation of dephosphorylated myosin was unaffected by the ad dition of MHC821-835 up to 30 mu M. The filaments formed in the presen ce of MHC835-846 were observed by electron microscopy to be morphologi cally indistinguishable from those formed in the absence of the peptid e, Rotary shadowed images of dephosphorylated myosin monomers revealed mostly the 10S form in the absence of MHC835-846, while the 6S form w as predominant in the presence of the peptide, The results indicate th at MHC835-846 inhibits the formation of the 10S conformation, On cosed imentation assaying with myosin, rod and light meromyosin, MKC835-846 bound to each of them with a stoichiometry of nearly 1 mol/mol heavy c hain, Altogether, these results suggest that the region in the myosin heavy chain corresponding to MHC835-846 may be involved in the binding site for the light meromyosin portion of myosin for formation of the 10S conformation,