CLEFT CONTAINING REACTIVE THIOL OF MYOSIN CLOSES DURING ATP HYDROLYSIS

The probe binding cleft of myosin subfragment 1 (S1) contains the reac tive thiol, SH1, and tryptophan 510 (Trp-510). Solvent accessibility t o Trp-510, measured using the acrylamide quenching of its fluorescence , is highest in rigor and decreases during the ATPase cycle prior to f orce generation. These data suggest the probe binding cleft closes dur ing ATP hydrolysis and opens during force generation. The closing of t he probe binding cleft may be the origin of the shape change of S1 dur ing ATP hydrolysis.