Structural changes of cross-bridges on transition from isometric to shortening state in frog skeletal muscle.
Structural changes in the myosin cross-bridges were studied by small-angle x-ray diffraction at a time resolution of 0.53 ms. A frog sartorius muscle, which was electrically stimulated to induce isometric contraction, was released by approximately 1% in 1 ms, and then its length was decreased to allow steady shortening with tension of approximately 30% of the isometric level. Intensity of all reflections reached a constant level in 5-8 ms. Intensity of the 7.2-nm meridional reflection and the (1,0) sampling spot of the 14.5-nm layer line increased after the initial release but returned to the isometric level during steady shortening. The 21.5-nm meridional reflection showed fast and slow components of intensity increase. The intensity of the 10.3-nm layer line, which arises from myosin heads attached to actin, decreased to a steady level in 2 ms, whereas other reflections took longer, 5-20 ms. The results show that myosin heads adapt quickly to an altered level of tension, and that there is a distinct structural state just after a quick release.
Yagi
Naoto
N
SPring-8/JASRI, 1-1-1 Kouto, Sayo, Hyogo, Japan. yagi@spring8.or.jp
Iwamoto
Hiroyuki
H
Inoue
Katsuaki
K
D000199:Actins / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D000818:Animals; D001703:Biophysics / Q000379:methods; D006868:Hydrolysis; D008962:Models, Theoretical; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D009218:Myosins / Q000737:chemistry; D017785:Photons; D011487:Protein Conformation; D011892:Rana catesbeiana / Q000378:metabolism; D013696:Temperature; D013997:Time Factors; D014961:X-Ray Diffraction
D000199:Actins; D000255:Adenosine Triphosphate; D009218:Myosins