Skeletal muscle myosin subfragment-1 induces bundle formation by actin filaments.
As is well known, the light scattering intensity of F-actin solutions increases immediately upon formation of the rigor complex with subfragment-1 (S-1). We have found that after the initial rise in scattering, there is a further gradual increase in scattering (we call it "super-opalescence"). Fluorescence and electron microscopic observations of acto-S-1 solutions showed that super-opalescence results from formation of actin filament bundles once S-1 binds to F-actin. The actin bundles possessed transverse stripes with a periodicity of about 350 A, which suggested that in the bundles actin filaments are arranged in parallel register. The rate of the initial process of bundle formation (i.e. side-by-side dimerization) could be approximately estimated by measuring the initial rate of super-opalescence (V0). V0 had a maximum (V0m) at a molar ratio of S-1 to actin of 1;6-1;7, regardless of the actin concentration, pH (6-8.5), Mg2+ concentration (up to 5 mM), or ionic strength (up to 0.3 M KC1). Lower pH, higher Mg2+ concentration, and higher ionic strength increased V0m; V0 was proportional to the square of the actin concentration, regardless of the solution conditions.
D000199:Actins / Q000378:metabolism*; D000818:Animals; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology; D008854:Microscopy, Electron; D009132:Muscles / Q000032:analysis; D015879:Myosin Subfragments; D009218:Myosins / Q000502:physiology*; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000502:physiology*; D011817:Rabbits; D012542:Scattering, Radiation; D012996:Solutions
D000199:Actins; D046911:Macromolecular Substances; D015879:Myosin Subfragments; D010446:Peptide Fragments; D012996:Solutions; D009218:Myosins; D008274:Magnesium