Effects of Ca2+ on the conformation and enzymatic activity of smooth muscle myosin.

摘要: The influence of Ca2+ on the enzymatic and physical properties smooth muscle myosin was studied. actin-activated ATPase activity phosphorylated gizzard heavy meromyosin is higher in presence than its absence, but this effect found only at lower MgCl2 concentrations. As concentration increased, sensitivity decreased. necessary to activate that required saturate calmodulin. similarity pCa dependence binding competition by Mg2+ indicate these effects involved Ca2+-Mg2+ sites myosin. For actin low concentrations MgCl2, both Vmax Ka are influenced Ca2+. formation small polymers could account for alteration affinity actin. concentrations, induces an increase Vmax. To detect alterations properties, two techniques were used: viscosity limited papain hydrolysis. dephosphorylated myosin, 6 S or 10 S, Ca2+-dependent not detected using either technique. However, decrease corresponding transition shifted KCl In addition, a proteolysis rates observed with ionic strength, i.e. under conditions where assumes folded conformation.