title: Actomyosin interactions in the presence of ATP and the N-terminal segment of actin.
abstract: The binding of myosin subfragment 1 (S-1) to actin in the presence of ATP and the acto-S-1 ATPase activities of acto-S-1 complexes were determined at 5 degrees C under conditions of partial saturation of actin, up to 90%, by antibodies against the first seven N-terminal residues on actin. The antibodies [Fab(1-7)] inhibited strongly the acto-S-1 ATPase and the binding of S-1 to actin in the presence of ATP at low concentrations of S-1, up to 25 microM. Further increases in S-1 concentration resulted in a partial and cooperative recovery of both the binding of S-1 to actin and the acto-S-1 ATPase while causing only limited displacement of Fab(1-7) from actin. The extent to which the binding and the ATPase activity were recovered depended on the saturation of actin by Fab(1-7). The combined amounts of S-1 and Fab binding to actin suggested that the activation of the myosin ATPase activity was due to actin free of Fab. Examination of the acto-S-1 ATPase activities as a function of S-1 bound to actin at different levels of actin saturation by Fab(1-7) revealed that the antibodies inhibited the activation of the bound myosin. Thus, the binding of antibodies to the N-terminal segment of actin can act to inhibit both the binding of S-1 to actin in the presence of ATP and a catalytic step in ATP hydrolysis by actomyosin. The implications of these results to the regulation of actomyosin interaction are discussed.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles 90024.
authors.forename: G
authors.initials: G
authors.lastname: DasGupta
authors.forename: E
authors.initials: E
authors.lastname: Reisler
mesh_terms: D000199:Actins / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D000205:Actomyosin / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D006868:Hydrolysis; D007140:Immunoglobulin Fab Fragments / Q000378:metabolism; D015879:Myosin Subfragments / Q000378:metabolism*; D010446:Peptide Fragments / Q000276:immunology / Q000378:metabolism*; D011817:Rabbits
chemical_list: D000199:Actins; D007140:Immunoglobulin Fab Fragments; D015879:Myosin Subfragments; D010446:Peptide Fragments; D000255:Adenosine Triphosphate; D000205:Actomyosin; D000251:Adenosine Triphosphatases