title: Effect of F-actin upon the binding of ADP to myosin and its fragments.
abstract: The effect of F-actin upon the binding of ADP to rabbit skeletal muscle myosin, heavy meromyosin, and subfragment 1 was studied by equilibrium dialysis, ultracentrifuge transport, and light scattering techniques. Both myosin and H-meromyosin (HMM) bind a maximum of approximately 1.6 mol of ADP/mol of protein, while S-1 binds approximately 0.9 mol of ADP/mol of protein. The affinity for ADP of all three preparations was similar at a given ionic strength (approximately 10(6) M-1 at 0.05 M KCl) and decreased with increasing ionic strength. Under conditions similar to those used for the measurement of ADP binding, the binding sites of myosin, HMM, and subfragment 1 (S-1) are saturated with actin at molar ratios of 2, 2, and 1 mol of actin monomer/mol of protein, respectively, as determined by light scattering, ultracentrifuge transport, and in the case of myosin by ATPase measurements. F-actin was found to inhibit ADP binding, but even at an actin concentration at least twice that required for saturation of myosin, HMM, or S-1, significant ADP binding remained. This ADP binding was inhibited by 10(-4) M pyrophosphate. The observations are consistent with the formation of an actomyosin-ADP complex in which actin and ADP are bound to myosin at distinct but interacting sites.
mesh_terms: D000199:Actins / Q000494:pharmacology*; D000244:Adenosine Diphosphate / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008027:Light; D008274:Magnesium / Q000494:pharmacology; D009132:Muscles / Q000378:metabolism; D015879:Myosin Subfragments / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D011485:Protein Binding; D011817:Rabbits; D012542:Scattering, Radiation
chemical_list: D000199:Actins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D000244:Adenosine Diphosphate; D000251:Adenosine Triphosphatases; D009218:Myosins; D008274:Magnesium