  We discovered novel enzyme kinetics of F$_1$-ATPase, a biomolecular motor
that synthesizes and hydrolyzes adenosine triphosphate (ATP), using
single-molecule experiments and numerical simulations. The enzyme kinetics of
F$_1$-ATPase followed the Michaelis-Menten equation in ATP hydrolysis but
deviated from it in ATP synthesis, indicating asymmetric enzyme kinetics
between ATP synthesis and hydrolysis. Numerical analysis based on a theoretical
model revealed a bypass mechanism underlying asymmetric enzyme kinetics. In
particular, we found that the origin of the asymmetric enzyme kinetics lies in
the asymmetry of the allosterism, not in the asymmetry of potential shapes. The
asymmetric enzyme kinetics may suggest that F$_1$-ATPase is designed to sustain
the rate of ATP synthesis while suppressing the futile ATP consumption.
