F1-ATPase, a rotary motor enzyme, can catalyse ATP hydrolysis in which the central γ-subunit ratates inside the α3β3 cylinder. Here, a four-state catalytic model of F1-ATPase is studied in which we think that the ATP hydrolysis and synthesis are ATP-dependent and ADP/Pi-dependent, respectively. The results show that the catalytic ratation mechanism of F1-ATPase is affected distinctly by the ATP/ADP/Pi concentrations. The model accords well with the expermental observations. Moreover, when the external load exists, the mean rotation rate of F1-ATPase is also affected apparently, and the external torque which decreases the mean ratation rate of the F1 motor to zero equals to the constant one which is produced during the ratation of the motor.
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