9603858 Kawai The long range goal of this research is to document the molecular mechanisms of contraction in skeletal muscle cells. The specific aim of this proposal is to determine the intermediate metabolic products and characterize the kinetic constants of the chemical reactions between the metabolic products. Skinned muscle fibers, in which the cell membrane has been removed by chemical treatment, are used so that ions and molecules of experimental interest can be placed into the muscle cells. A step length change is applied to muscle fibers during maximal activation, which, in turn, induces a change in tension. From the time course of tension, three time constants are obtained and these are studies as functions of ATP (the energy source), ADP (a product), and phosphate (another product) concentrations. Dr. Kawai is also able to observe the ATP hydrolysis rate, which characterizes the slowest chemical reaction. From these data the ten kinetic constants which characterize the chemical steps between individual metabolic products are deduced. These procedures will allow for the rigorous testing of many hypotheses including step-length dependence of the chemical reactions. The proposed studies will yield answers to questions that cannot be obtained from studies of purified muscle proteins.
