Heat (30°C)-Desensitization of Akazara Striated Adductor Myosin, and Its Resensitization

In a previous report (J. Biochem. 89, 1333–1335, 1981) we showed that 30°C-treat-ment (pCa < 6 and 2 mM MgCl2), like EDTA-treatment, caused a reversible removal of regulatory light-chains from Akazara adductor myosin. Utilizing the heat-treatment, we now show (a) that not half but the total removal of regulatory light-chains from Akazara myosin is required for a complete loss of calcium sensitivity of myo-sin-ATPase, and (b) that recombination of not 1 but 2 mol of regulatory light-chains is required for a full recovery of calcium sensitivity of both myosin-ATPase and actomyosin-superprecipitation. These (a, b) are what we showed previously with EDTA-treatment (J. Biochem. 85, 1543–1546, 1979 and 86, 663–673, 1979), thus establishing that in all respects we tested, the heat-treatment is as good as EDTA-treatment for reversible removal of regulatory light-chains. We also show that the presence of actin during heat-treatment of myosin prevented regulatory light-chains from being released (at pCa 7) and that how well the release was prevented depended on the MgCl2 concentration during the heat-treatment.