Effect of activation by calcium on the X-ray diffraction pattern from insect flight muscle

• Published in: Journal of molecular biology Vol. 92; no. 1; pp. 39 - 53
• Main Authors: Armitage, P.M., Tregear, R.T., Miller, A.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 15.02.1975
• Subjects: Actins - metabolism; Animals; arthropods; Calcium - pharmacology; entomology; Flight, Animal; Hemiptera - metabolism; insects; Macromolecular Substances; Muscle Contraction - drug effects; Muscles - drug effects; Muscles - metabolism; Muscles - ultrastructure; Myosins - metabolism; Oscillometry; Protein Binding; Time Factors; X-Ray Diffraction
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/0022-2836(75)90090-X

A low-angle X-ray diffraction pattern of calcium-activated Lethocerus flight muscle was formed and the intensities of various parts of the pattern observed by means of a proportional counter. The muscle was sinusoidally oscillated in length to produce mechanical work. The resultant changes in diffraction intensity were related to the state of the muscle and to the phase of the mechanical oscillatory cycle. The measurements were interpreted in terms of a movement of the heads of the myosin molecules into contact with the actin filaments. In these terms the results showed that between 10 and 20% of the myosin heads attached to actin during work-producing oscillation of the muscle. The time-course of this attachment followed that of tension generation with a small delay. Calculation suggests that not all of the myosin molecules attached to actin at any one moment were generating tension.