F-1-ATPase hydrolyzes ATP into ADP and Pi and converts chemical energy into mechanical rotation with exceptionally high efficiency. This energy-transducing molecular motor increasingly attracts interest for its unique cellular functions and promising application in nanobiotechnology. To better understand the chemomechanics of rotation and loading dynamics of F-1-ATPase, we propose a computational model based on enzyme kinetics and Langevin dynamics. We show that the torsional energy and stepwise rotation can be regulated by a series of near-equilibrium reactions when nucleotides bind or unbind, as well as characterized by an effective "ratchet" drag coefficient and a fitting chemomechanic coefficient. For the case of driving an actin filament, the theoretical load-rotation profile is analyzed and comparison with experimental data indicates reasonable agreement. The chemomechanics described in this work is of fundamental importance to all ATP-fueled motor proteins. (C) 2003 American Institute of Physics.