Journal of Molecular Biology
Volume 75, Issue 1, 25 March 1973, Pages 33-34, IN13-IN14, 35-55
Journal home page for Journal of Molecular Biology

Structural role of tropomyosin in muscle regulation: Analysis of the X-ray diffraction patterns from relaxed and contracting muscles

https://doi.org/10.1016/0022-2836(73)90527-5Get rights and content

Abstract

Previous work has shown that there are significant differences in the X-ray diffraction patterns obtained from relaxed and contracting muscles. We show that some of these changes can be explained in terms of a small movement (~ 5 to 15 Å) of the tropomyosin molecules in the groove of the actin helix. The position of the tropomyosin in relaxed skeletal muscle is such that it might physically block or at least structurally alter the cross-bridge attachment site on actin, whereas in contracting skeletal muscle the tropomyosin moves to a position well clear of the attachment site. The movement of the tropomyosin molecules is apparently smaller in molluscan muscles during tonic contraction than in vertebrate skeletal muscle. We suggest a possible relationship between the smaller movement of the tropomyosin and the “catch” response of molluscan muscles.

We also show that any increase of intensity on the 59 Å and 51 Å layer-lines is most likely to be associated with some extra mass (HMM S-1) attaching to the actin molecules. Such a change cannot be explained in terms of a change in tropomyosin structure or in the order within the thin filaments. Since changes on these two layer-lines have been observed during contraction, this provides good evidence for cross-bridge attachment to actin in contracting muscles.

References (31)

  • D.L.D. Caspar et al.

    J. Mol. Biol

    (1969)
  • S. Ebashi et al.

    Progr. Biophys. Mol. Biol

    (1968)
  • J. Hanson et al.

    J. Mol. Biol

    (1963)
  • H.E. Huxley

    J. Mol. Biol

    (1968)
  • H.E. Huxley et al.

    J. Mol. Biol

    (1967)
  • S. Lowey et al.

    J. Mol. Biol

    (1969)
  • G.R. Millward et al.

    J. Mol. Biol

    (1970)
  • P.B. Moore et al.

    J. Mol. Biol

    (1970)
  • E.F. Woods

    J. Biol. Ghem

    (1967)
  • K. Bailey

    Biochem. J

    (1948)
  • C. Cohen et al.
  • C. Cohen et al.

    Science

    (1966)
  • C. Cohen et al.

    J. Amer. Chem. Soc

    (1957)
  • M.H. Draper et al.

    Aust. J. Exp. Biol. Med. Sci

    (1949)
  • S. Ebashi et al.

    J. Biochem

    (1971)
  • Cited by (0)

    Present address: Biopolymer Group, Department of Metallurgy, Imperial College, London SW7 2BP, England.

    View full text