title: Pre-steady-state kinetic evidence for a cyclic interaction of myosin subfragment one with actin during the hydrolysis of adenosine 5'-triphosphate.
abstract: A single cycle of adenosine 5'-triphosphate (ATP) hydrolysis by a complex of actin and myosin subfragment one (acto-S-1) was studied in a stopped-flow apparatus at low temperature and low ionic strength, using light scattering to monitor the interaction of S-1 with actin and fluorescence to detect the formation of fluorescent intermediates. Our results show that the addition of a stoichiometric concentration of ATP to the acto-S-1 causes a cycle consisting of first, a rapid dissociation of the S-1 from actin by ATP; second, a slower fluorescence change in the S-1 that may be related to the initial phosphate burst; and third, a much slower rate limiting recombination of the S-1 with actin. This latter step equals the acto-S-1 steady-state adenosine 5'-triphosphatase (ATPase) rate at both low and high actin concentrations, and like the steady-state ATPase levels off at a V max of 0.9s-1 at high actin concentration. Therefore, the release of adenosine 5'-diphosphate and inorganic phosphate is not the rate-limiting step in the acto-S-1 ATPase. Rather, a slow first-order step corresponding to the previously postulated transition from the refractory to the nonrefractory state precedes the rebinding of the S-1 to the actin during each cycle of ATP hydrolysis.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D007700:Kinetics; D008956:Models, Chemical; D009218:Myosins / Q000378:metabolism*; D009391:Nephelometry and Turbidimetry; D010446:Peptide Fragments / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D011485:Protein Binding; D012542:Scattering, Radiation; D013050:Spectrometry, Fluorescence
chemical_list: D000199:Actins; D010446:Peptide Fragments; D010710:Phosphates; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D009218:Myosins