title: Cause of changes in the thin filament-associated reflexions on activation of frog muscle--myosin binding or conformational change of actin.
abstract: Although the intensity increase of the 5.9 nm layer-line (5.9 L.L.) on activation can potentially be informative, systematic investigation is left to be done. The present study is aimed to assign the cause of the intensity increase. Using the synchrotron radiation, X-ray diffraction patterns were recorded from live sartorius or semitendinosus muscle of the frog (mostly at a temperature of 3-4 degrees C) either on the "Imaging Plates", a newly developed X-ray image recording system, or with the fast linear detector. The Imaging Plates enabled us to measure the disorientation of the thin filaments in the contracting muscle, so that the intensity profiles of the layer-lines were corrected for the disorientation. After the correction, a slight inward shift of the intensity peak of 5.9 L.L. was measured which is associated with the intensity increase on activation at 4 degrees C. At higher temperatures, 5.9 L.L. increases less. The extent of the intensity increase is linearly related to the sarcomere overlap, whereas the outer part of the 2nd actin layer-line (2nd L.L.) is as high as 60% at 10% overlap. The rise of the intensity of 5.9 L.L. is as fast as that of 2nd L.L., but much faster than the changes of the equatorial reflexions and the tension rise. Although these results do not let us assign the cause, some properties are elucidated of the structural change which causes the intensity increase.
authors.affiliation: European Molecular Biology Laboratory, Hamburg Outstation, F. R. Germany.
authors.forename: Y
authors.initials: Y
authors.lastname: Maéda
authors.forename: D
authors.initials: D
authors.lastname: Popp
authors.forename: S M
authors.initials: SM
authors.lastname: McLaughlin
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D066298:In Vitro Techniques; D007700:Kinetics; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*; D009210:Myofibrils / Q000502:physiology*; D009218:Myosins / Q000378:metabolism*; D011487:Protein Conformation; D011895:Rana ridibunda; D012518:Sarcomeres / Q000502:physiology* / Q000648:ultrastructure; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D000199:Actins; D009218:Myosins