Energy transduction of isothermal ratchets: Generic aspects and specific examples close to and far from equilibrium

We study the energetics of isothermal ratchets which are driven by a chemic al reaction between two states, and operate in contact with a single heat b ath of constant temperature. We discuss generic aspects of energy transduct ion such as Onsager relations in the linear response regime as well as the efficiency and dissipation close to and far from equilibrium. In the linear response regime where the system operates reversibly, the efficiency is in general nonzero. Studying the properties for specific examples of energy l andscapes and transitions, we observe in the linear response regime that th e efficiency can have a maximum as a function of temperature. Far from equi librium in the fully irreversible regime, we find a maximum of the efficien cy with values larger than in the linear regime for an optimal choice of th e chemical driving force. We show that the corresponding efficiencies can b e of the order of 50%. A simple analytical argument allows us to estimate t he efficiency in this irreversible regime for small external forces. [S1063 -651X(99)01708-0].