title: An intact heavy chain at the actin-subfragment 1 interface is required for ATPase activity of scallop myosin.
abstract: Scallop S1 has a region sensitive to tryptic hydrolysis not found thus far in S1s of other species, located 65K from the N-terminus as determined by SDS/polyacrylamide-gel electrophoresis. In the presence of actin the S1 heavy chain is preferentially cleaved at this site. The high-salt EDTA and calcium ATPase activities of the nicked 65K-31K S1 are abolished. This inactivation is not due to denaturation, conformational effects of actin, or to light chain dissociation. The unique proteolytic site of scallop S1 is adjacent to a peptide involved in actin-S1 interaction in scallop and rabbit but it is far removed from the nucleotide-binding site in the linear amino acid sequence. We conclude that proteolysis inactivates the high-salt ATPase activities through a connection mediated by tertiary interactions. Such a connection provides a structural correlate for the known reciprocal relationship between the nucleotide and actin affinities of myosin.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D008970:Molecular Weight; D008974:Mollusca; D015879:Myosin Subfragments; D009218:Myosins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D011485:Protein Binding; D011817:Rabbits; D013329:Structure-Activity Relationship; D013696:Temperature; D014357:Trypsin
chemical_list: D000199:Actins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D014357:Trypsin; D000251:Adenosine Triphosphatases; D009218:Myosins