SULFHYDRYL-GROUPS INVOLVED IN THE ACTIVE-SITE OF MYOSIN-B ADENOSINE-TRIPHOSPHATASE .6. POSSIBLE ROLE OF SA IN THE MYOSIN-ACTIN INTERACTION

To clarify further the mechanism of Mg2+ activation of myosin B by the modification of Sa, a specific sulfhydryl group in the light meromyosin (LMM) region, the properties of Sa blocked myosin B, myosin A, and LMM were investigated in comparison with those of unmodified materials and the following results were obtained.An Arrhenius plot of Mg2+-ATPase activity of myosin B showed that the frequency factor became larger on blocking Sa whereas the activation energy was not affected.Mg2+ATPase activity of myosin B as well as Mg activity was activated by the modification, whereas Mg2+ activity was not affected.The inhibition of Mg2+ activity of myosin B at higher magnesium concentration disappeared on entrapment of myosin B into agarose gel, and even an entrapped and unmodified sample had the same Mg concentration dependency as that of soluble Sa myosin B.The Mg2+-ATPase activity of modified myosin A separated from S myosin B was rapidly enhanced and saturated by a lower concentration of actin than that for unmodified myosin A.It was shown by electron microscopy that myosin and actin filaments of Sa myosin B in the presence of Mg2+ gathered in parallel while in the case of unmodified myosin B they dispersed each other.Synthetic myosin filaments and LMM paracrystals of Sa materials were indistinguishable from those of the unmodified compounds electron microscopically.Based on these results and previously described properties of Sa myosin B, the mechanism of the participation of Sa in the myosin-actin interaction is discussed. © 1979 By The Journal Of Biochemistry.