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J. Biochem, 1977, Vol. 81, No. 4 933-939
© 1977 Japanese Biochemical Society

research-article

The Sulfhydryl Groups Involved in the Active Site of Myosin B Adenosinetriphosphatase

II. Effect of Modification of the Sa Thiol Group on Superprecipitation and Clearing

Tatsuhisa YAMASHITA and Tsuneyoshi HORIGOME

Laboratory of Physiological Chemistry, School of Medicine, Juntendo University Bunkyo-ku, Tokyo 113

The effect of S2 modification with NEM, which activates Mg2+-ATPase through an enhancement of the association of actin and myosin, wa investigated on the superprecipitation, clearing and Mg2+-ITPase of myosin B with reference to the effect of S1-blocking.

  1. Superprecipitation induced by ATP was markedly enhanced by S2-blocking even at high concentrations of Mg2+ and substrate; this may be due to an increase in the affinity of myosin and actin on blocking S2.
  2. Nevertheless, neither ITP-induced superprecipitation nor Mg2+ was affected by S2, modification.
  3. Blocking of S1 brought about the inhibition of ATP- and ITP-induced superprecipitation and Mg2+ activity, suggesting that S1 decreases the affinity of myosin and actin.
  4. S2-blocked myosin B showed greater resistance to clearing by ATP, especially in the presence of Ca2+ ions, whereas in the clearing response of actomyosin gel to PP1 no difference between S2-blocked and unmodified myosins B was observed. On the other hand, the clearing response of myosin B became more sensitive to both ATP and PP1 on blocking S1.

Based on the above results and preliminary data suggesting that S2 is located in LMM, the interaction of myosin filaments and actin filaments under physiological conditions is discussed.


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