title: Polymerization of G-actin by myosin subfragment 1.
abstract: The polymerization of actin from rabbit skeletal muscle by myosin subfragment 1 (S-1) from the same source was studied in the depolymerizing G-actin buffer. The polymerization reactions were monitored in light-scattering experiments over a wide range of actin/S-1 molar rations. In contrast to the well resolved nucleation-elongation steps of actin assembly by KC1 and Mg2+, the association of actin in the presence of S-1 did not reveal any lag in the polymerization reaction. Light scattering titrations of actin with S-1 and vice versa showed saturation of the polymerization reaction at stoichiometric 1:1 ratios of actin to S-1. Ultracentrifugation experiments confirmed that only stoichiometric amounts of actin were incorporated into a 1:1 acto-S-1 polymer even at high actin/S-1 ratios. These polymers were indistinguishable from standard complexes of S-1 with F-actin as judged by electron microscopy, light scattering measurements, and fluorescence changes observed while using actin covalently labeled with N-(1-pyrenyl)iodoacetamide. F-actin obtained by polymerization of G-actin by S-1 could initiate rapid assembly of G-actin in the presence of 10 mM KC1 and 0.5 mM MgCl2 and showed normal activation of MgATPase hydrolysis by myosin.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D007700:Kinetics; D008027:Light; D008854:Microscopy, Electron; D015879:Myosin Subfragments; D009218:Myosins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D011108:Polymers; D011817:Rabbits; D012542:Scattering, Radiation
chemical_list: D000199:Actins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D011108:Polymers; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins