title: Evidence for pre- and post-power stroke of cross-bridges of contracting skeletal myofibrils.
abstract: We examined the orientational fluctuations of a small number of myosin molecules (approximately three) in working skeletal muscle myofibrils. Myosin light chain 1 (LC1) was labeled with a fluorescent dye and exchanged with the native LC1 of skeletal muscle myofibrils cross-linked with 1-ethyl-3-[3(dimethylamino) propyl] carbodiimide to prevent shortening. We observed a small volume within the A-band (∼10(-15) L) by confocal microscopy, and measured cyclic fluctuations in the orientation of the myosin neck (containing LC1) by recording the parallel and perpendicular components of fluorescent light emitted by the fluorescently labeled myosin LC1. Histograms of orientational fluctuations from fluorescent molecules in rigor were represented by a single Gaussian distribution. In contrast, histograms from contracting muscles were best fit by at least two Gaussians. These results provide direct evidence that cross-bridges in working skeletal muscle assume two distinct conformations, presumably corresponding to the pre- and post-power-stroke states.
authors.affiliation: Department of Molecular Biology and Immunology, University of North Texas Health Science Center, Fort Worth, Texas, USA.
authors.forename: K
authors.initials: K
authors.lastname: Midde
authors.forename: R
authors.initials: R
authors.lastname: Luchowski
authors.forename: H K
authors.initials: HK
authors.lastname: Das
authors.forename: J
authors.initials: J
authors.lastname: Fedorick
authors.forename: V
authors.initials: V
authors.lastname: Dumka
authors.forename: I
authors.initials: I
authors.lastname: Gryczynski
authors.forename: Z
authors.initials: Z
authors.lastname: Gryczynski
authors.forename: J
authors.initials: J
authors.lastname: Borejdo
mesh_terms: D000818:Animals; D016880:Anisotropy; D005454:Fluorescence Polarization; D021621:Imaging, Three-Dimensional; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D009210:Myofibrils / Q000187:drug effects / Q000502:physiology*; D018994:Myosin Light Chains / Q000378:metabolism; D016011:Normal Distribution; D011817:Rabbits; D012235:Rhodamines / Q000494:pharmacology; D012518:Sarcomeres / Q000502:physiology; D013997:Time Factors
chemical_list: D018994:Myosin Light Chains; D012235:Rhodamines; C034996:tetramethylrhodamine iodoacetamide