Calcium-dependent structural changes in scallop heavy meromyosin

摘要: The mechanism of calcium regulation scallop myosin is not understood, although it known that both heads are required. We have explored possible interactions between the heavy meromyosin (HMM) in presence and absence nucleotides by sedimentation electron microscope studies. ATPase activity HMM preparation was activated over tenfold calcium, indicating contained mostly regulated molecules. In ADP or ATP analogs, increased asymmetry molecule as judged its slower velocity compared with EGTA. nucleotide high even shift occurred a sharp midpoint at level about 0.5 microM. Sedimentation subfragment 1 dependent on nucleotides. Modeling accounted for observed behavior assuming bent toward tail while had random positions. pattern showed single peak all concentrations, equilibration two forms t(1/2) less than 70 seconds. Electron micrographs crosslinked, rotary shadowed specimens indicated 81 % molecules pointing back towards 41 presence. This consistent data. conclude "off" state, interact each other, forming rigid structure low activity. When switched "on" binding communication lost, allowing them to flex randomly junction tail; this could facilitate their interaction actin contracting muscle.