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Journal of Muscle Research & Cell Motility

, Volume 25, Issue 4–5, pp 329–335 | Cite as

Intensity of X-ray reflections from skeletal muscle thin filaments partially occupied with myosin heads: effect of cooperative binding

  • Takumi Tamura
  • Jun'ichi Wakayama
  • Tetsuro Fujisawa
  • Naoto Yagi
  • Hiroyuki Iwamoto
Article

Abstract

For quantitative analysis of contractile proteins of muscle by means of X-ray diffraction, it is important to know how the intensities of individual reflections are related to the number of diffracting objects, i.e., the amount of constituent contractile protein in the muscle cell. Here we diffused various amounts of exogenous myosin subfragment-1 (S1) into overstretched skinned skeletal muscle fibers, either in the presence or absence of Ca2+ , and derived the relationship between the S1 content and the intensities of reflections arising from the S1. In theory, the intensities should be proportional to the square of the S1 content (square law). However, the intensity--content relation deviated systematically from the square law as the S1 content was lowered, and it was better described as a linear function at the lower end of the S1 contents (<20% of saturation level). Model calculations show that the way of deviation is explained by the cooperative manner of S1 binding to the regulated thin filament.

X-ray diffraction skeletal muscle fibers myosin subfragment-1 thin filament cooperativity synchrotron radiation 

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Copyright information

© Kluwer Academic Publishers 2004

Authors and Affiliations

  • Takumi Tamura
    • 1
  • Jun'ichi Wakayama
    • 1
  • Tetsuro Fujisawa
    • 1
  • Naoto Yagi
    • 2
  • Hiroyuki Iwamoto
    • 2
  1. 1.Structural Biochemistry LaboratoryRIKEN Harima InstituteJapan
  2. 2.Life and Environment DivisionJapan Synchrotron Radiation Research InstituteJapan

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