title: Fraction of myosin cross-bridges bound to actin in active muscle fibers: estimation by fluorescence anisotropy measurements.
abstract: Time-resolved and steady-state fluorescence anisotropy measurements from fluorescence-labeled myosin cross-bridges in single glycerinated skeletal muscle fibers in rigor, relaxed, MgADP-induced, and contracting states have been made in order to estimate the fraction of actin-bound cross-bridges in active muscle. When the plane of polarization of the excitation light is perpendicular to the fiber axis and its propagation vector has a component parallel to this axis, actin-bound cross-bridge states, such as rigor and MgADP-induced, have time-zero and steady-state anisotropies that are substantially lower than has the relaxed state. This difference provides a means of determining the fraction of cross-bridges bound to actin in active isometric fibers, by comparing the fluorescence anisotropy from active fibers with the anisotropy from bound and unbound cross-bridges in static states. By assuming that the active cross-bridges are either bound (in the manner of rigor or MgADP-induced states) or relaxed, we estimate that greater than 80% of the cross-bridges are actin-bound in active isometric fibers.
mesh_terms: D000199:Actins / Q000378:metabolism; D000205:Actomyosin; D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D005454:Fluorescence Polarization; D009119:Muscle Contraction; D009218:Myosins / Q000378:metabolism; D011485:Protein Binding; D011817:Rabbits
chemical_list: D000199:Actins; D000244:Adenosine Diphosphate; D000205:Actomyosin; D009218:Myosins