KINETICS OF THE ON OFF CHANGE IN REGULATORY STATE OF THE MUSCLE THIN FILAMENT

The excimer fluorescence of pyrene iodoacetamide-labeled tropomyosin bound to actin is a probe of the regulatory state change of the muscle thin filament associated with the cooperative binding of myosin subfragment 1 (S1) (Y. Ishii and S.S. Lehrer, Biochemistry 29, 1160, 1990). In this study, the excimer fluorescence was used to monitor the kinetics of the 'on-off' state change due to the ATP-induced dissociation of S1 from actin-tropomyosin. A lag in the fluorescence change indicated that the thin filament was maintained in the 'on-state' until more than half of the S1s dissociate. The on-off transition rate was slower than the dissociation of the remaining S1s. These delays in relaxation to the 'off-state' may explain some observed kinetic and cooperative effects during tension measurements. © 1993 Academic Press, Inc.