A novel electron paramagnetic resonance spin label and its application to study the cross-bridge cycle

摘要: We have used a novel alpha-iodoketone spin-label (IKSL) to study myosin head orientation and cross-bridge dynamics in the putative pre-powerstroke state. Possible perturbation of cycle by label was assayed sinusoidal analysis method (Kawai Brandt, 1980; Kawai Zhao, 1993), which determines rate constants elementary steps cycle. A comparison rates obtained from unlabeled IKSL fibers revealed small (10-20%) changes ATP hydrolysis steps. The labeling induced (< 13%) distribution cross-bridges among various intermediate states. Pre-powerstroke were aluminum fluoride presence Ca2+ ATP. In this state, force development is inhibited, but large proportion (40%) are still attached thin filament. conventional electron paramagnetic resonance measure orientation, found that heads as disordered relaxation. Their mobility, determined saturation transfer resonance, significantly restricted. Assuming stiffness proportional fraction strongly heads, rotational correlation time bound estimated be tau r = approximately 150-400 microseconds.