title: Dual effect of Ca2+ on ultrasonic ATPase activity and polymerization of muscle actin.
abstract: Millimolar concentrations of Ca2+ stimulate actin polymerization whereas micromolar concentrations of Ca2+ depress polymerization. This latter effect leads to a reduction of ATPase (ATP phosphohydrolase, EC 3.6.1.3) activity of actin during sonication at low Mg2+ concentrations and in the absence of KCl. In the presence of KCl (90 mM) there is activation of ATPase activity by micromolar Ca2+ concentrations. These Ca2+ effects are half-maximal at a Ca2+ concentration of 2-10(-7) M. They can be explained by assuming that that ATPase activity is optimal in a medium range of actin polymer stability and that micromolar Ca2+ concentrations tend to labilize and depolymerize F-actin.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology*; D004355:Drug Stability; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology; D008956:Models, Chemical; D009994:Osmolar Concentration; D011189:Potassium Chloride; D013010:Sonication
chemical_list: D000199:Actins; D046911:Macromolecular Substances; D004533:Egtazic Acid; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D008274:Magnesium; D002118:Calcium