title: Interactions of the actin and nucleotide binding sites on myosin subfragment 1.
abstract: The effects of selected nucleotides (N) on the binding of myosin subfragment 1 (S-1) and pure F-actin (A) were measured by time-resolved fluorescence depolarization for 0.15 M KCl, pH 7.0 at 4 degrees. The association constants K'A, KN, and K'N in the scheme (see article), were determined for the magnesium salts of ADP, adenyl-5'-yl imidodiphosphate AMP-P(NH)P, and PPi. The nucleotide binding site on S-1 was "mapped" with respect to its interaction on the actin binding site. The subsites were the beta- and gamma-phosphoryl groups of ATP bind had the largest effects. A quantitative measure of the interaction, the interaction free energy, was defined as -RT ln (KA/K'A). For ADP, K'A was 2.7 X 10(5) M-1 and the interaction free energy was -4.67 kJ M-1. For AMP-P(NH)P and PPi it was much larger. A ternary complex was shown to exist for ADP, S-1, and actin in the presence of Mg2+ and evidence from AMP-P(NH)P and PPi measurements indicated that ATP also likely forms a ternary complex. The mechanism of (S-1)-actin dissociation is discussed in light of these results.
mesh_terms: D000199:Actins / Q000378:metabolism; D000227:Adenine Nucleotides / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000266:Adenylyl Imidodiphosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D011756:Diphosphates / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008274:Magnesium; D009218:Myosins / Q000378:metabolism; D011485:Protein Binding
chemical_list: D000199:Actins; D000227:Adenine Nucleotides; D011756:Diphosphates; D046911:Macromolecular Substances; D000266:Adenylyl Imidodiphosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D009218:Myosins; D008274:Magnesium