title: Single turnover of cross-bridge ATPase in rat muscle fibers studied by photolysis of caged ATP.
abstract: A mechanical study on skinned rat psoas muscle fibers was performed at about 16 degrees C with X-ray diffraction and caged-ATP photolysis. The amount of photoreleased ATP was set < 0.2 mM for analysis of a 'single turnover' of the cross-bridge ATPase. With regard to the phase of activation, the results under the single turn-over condition were generally consistent with previous results obtained with larger amount of photoreleased ATP. Formation of the ADP-rigor state was mechanically monitored by the 90 degrees out-of-phase component of stiffness at 500 Hz, which was elevated on activation and then decreased to zero with a half-time of 0.2-0.3 s. Intensity changes of the X-ray reflections (e.g. equatorial reflections, actin layer lines and a myosin meridional reflection) indicated that a large number of cross-bridges returned to the rigor structure with a half-time of 0.5-0.7 s. During this phase, tension did not increase but slowly decreased with a half-time of about 1.0 s. The in-phase stiffness increased only 20-30% at the most. These results indicate that, even if the number of cross-bridges formed at any moment during full contraction is small, they can interact with actin and form rigor bonds with a rate of 1 s(-1). The force developed in the rigor formation is probably lost due to the presence of rigor bridges and compliance in the preparation.
authors.affiliation: Department of Physiology, Oita Medical University, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Horiuti
authors.forename: N
authors.initials: N
authors.lastname: Yagi
authors.forename: S
authors.initials: S
authors.lastname: Takemori
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000528:radiation effects; D000818:Animals; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004789:Enzyme Activation; D007537:Isometric Contraction / Q000502:physiology; D046911:Macromolecular Substances; D018485:Muscle Fibers, Skeletal / Q000201:enzymology*; D009218:Myosins / Q000378:metabolism*; D010782:Photolysis; D025941:Protein Interaction Mapping; D016658:Psoas Muscles / Q000201:enzymology / Q000648:ultrastructure; D051381:Rats; D014961:X-Ray Diffraction
chemical_list: D046911:Macromolecular Substances; D000244:Adenosine Diphosphate; C029273:P(3)-1-(2-nitro)phenylethyladenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D009218:Myosins