抄録
The relaxing protein was purified from the minor component of metin by DEAE cellulose column chromatography. Myosin B was usually desensitized by washing with 2mM NaHCO3. The following results were obtained on the regulation by the relaxing protein and MgATP, of the Mg++-activated ATPase of actomyosin.
1) In the presence of Ca++, the ATPase of actomyosin was activated by the relaxing protein when the concentration of MgATP was low (10-5-5×10-4M). The maximal rate of ATP hydrolysis was observed at 10-4M of MgATP. At higher concentrations of substrate, the ATPase was inhibited. The relaxing protein lowered the substrate concentration at which the ATPase of actomyosin was inhibited by the substrate itself. In the absence of Ca++, the substrate inhibition was further potentiated and occurred at much lower concentrations of MgATP.
2) When actomyosin was reconstituted from F-actin and myosin A which was pretreated with PCMB and β-mercaptoethanol, its ATPase activity was greatly enhanced by the relaxing protein even at high concentrations of MgATP (-4mM). The enhancement was more prominent in the presence of Ca++ than in its absence.
3) Troponin was removed from the relaxing protein by precipitation at pH 4.6. The precipitate activated the ATPase activity at low concentrations of the substrate both in the presence and absence of Ca++. In the presence of Ca++, the enhancement of substrate inhibition by the precipitate was larger than that by the original relaxing protein. But in the absence of Ca++, it was smaller than that by the parent protein.
