Studies on function of myosin subfragment-2 in skeletal muscle contraction

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Huxley, H.C.and Huxley, A.F.have independently proposed that structural changes (head rotation) in myosin subfragment-1 (S-1) region activated muscle fibers, whilee it is attached to actin, contribute to force generation. However there is no direct evidence supporting this mechanism until now. On the other hand, Harrington, W.F.has proposed that melting and shortening in the hinge region located between the short subfragment-2 and light meromyosin segments contribute to force generation in activated muscle fibers. We have shown that the antibody to whole myosin subfragment-2 (S-2) completely reduces the Ca^<2+>-activated force in glycerinated rabbit psoas muscle fibers without affecting the Ca^<2+>-activated ATPase activity. To obtain further information about the function of S-2 in muscle contraction coupled to the myosin hinge region, we purified an antibody directed against a 20-amino acid peptide segment within the hinge region of skeletal muscle myosin. Electron microscopy showed … More that a globular structure corresponding to an anti-hinge antibody bound at the hinge region of the myosin molecule.In relaxd single glycerinated fibers treated with anti S-2 hinge antibody (IgG,3mg/ml, 60min) , Ca^<2+>-activated isometric force and muscle fiber stiffness decreased in parallel without complete suppresion, in contrast Ca^<2+>-activated ATPase activity remained unchanged. In rigor single fibers done with, both isometric rigor force and muscle fiber stiffness did not changed. These results suggest that the hinge region does not strongly affect the function of muscle contraction, therefore another region of myosin subfragment-2 without the hinge region may contribute to muscle contraction. However, this possibility is unlikely that anti S-2 antibody against to antigen in 20-amino acid peptide of S-2 region closed to S-2-S-2 junction, much less reduces in Ca^<2+>-activated force. Whole region of myosin subfragment-2 may be important to muscle contraction mechanism, or antibody against to antigen in very limited small region may be no effective. Less