Individual States in the Cycle of Muscle Contraction

By using appropriate analogs of ATP, isometrically-held glycerol-extracted psoas fibers from rabbits are forced successively into states corresponding to molecular species in the contractile cycle. In each state measurements are made of Punk, a fluorescence polarization parameter thought to relate to attitude of S-1 moieties of the myosin molecules. Also, the value of Punk is measured during active tension development. It is suggested that this value is a time-average of the Punk as S-1 moieties move through the various states of the cycle. Proposals are made concerning the sequence of states in the cycle.