A major long range goal in the study of muscle contraction is to explain the physiological responses of muscle fibers in terms of the kinetics and energetics of the interaction of actin and myosin. The proposed work will approach this goal by measuring the mechanics of contraction of single permeable skeletal muscle fibers under a variety of conditions. These data will be used to refine models of the complex chemomechanics of the contractile interaction. Our previous work has characterized the effect of ligands on the shortening of fast skeletal fibers. An extension of this approach to slow muscle and to lengthening of fast and slow fibers will produce new data defining the interaction of MgATP and other ligands with the contractile proteins. Additional correlations linking muscle physiology to the biochemistry of the acto-S1 interaction will be determined by comparing the response of active fibers to the kinetics of the acto-S1 interacton using a series of different nucleotides modified at either the base or the ribose ring. In an extension of previous studies, using recently developed methods, studies originally performed at 10 degrees C will be performed at more physiological temperatures. Preliminary results show that the response of the fibers to alterations in MgATP or pH may be quite different at higher temperatures. Together the data obtained in the above studies will lead to a more detailed model of the energetics of the cross-bridge states involved in substrate binding and in product release. The results of this research will contribute to our understanding of the basic biochemical mechanisms underlying muscle contraction.
