Protein motor F ₁ as a model system for fluctuation theories of non-equilibrium statistical mechanics

F ₁-ATPase (F ₁) is a rotary motor protein in which the rotor γ subunit rotates in the α ₃β ₃ ring hydrolyzing adenosine-5′-triphosphate (ATP). Several fluctuation theories of nonequilibrium statistical mechanics have been applied recently to the single-molecule experiments on F ₁. For example, the fluctuation theorem, a recent achievement in the field of nonequilibrium statistical mechanics, has been suggested to be useful for measuring the rotary torque of F ₁. In this paper, we introduce F ₁ as a good biological model for experimentally testing the theories of nonequilibrium statistical mechanics.