Na,K-ATPase as a brownian motor: Electric field-induced conformational fluctuation leads to uphill pumping of cation in the absence of ATP

Na,K-ATPase uses chemical bond energy of ATP to pump K+ into, and Na+ out of a cell. Both are uphill transports. During the catalytic cycle the enzyme alternates between two conformational states, E-1 and E-2. This communication describes an experiment, which employs electric field to drive oscillation or fluctuation of enzyme conformation between the E-1 and the E-2 states. It is shown that the field-induced conformational oscillation or fluctuation leads to uphill pumping of the cation by the enzyme without consumption of ATP. Biochemical specificity of the catalysis is preserved. Data indicate that Na,K-ATPase can harvest energy from the applied electric field to perform chemical work, and a ratchet mechanism is inherent in this energy transduction process. A Theory of Electroconformational Coupling (TEC) that embodies essential features of the Brownian Ratchet successfully simulates the field-frequency and field-amplitude optima and other features of the ion pumping activity. A four-state TEC motor can achieve high efficiency of the energy transduction, asymptotically reaching 100% under the optimal condition. Pumping by ion rectification fails to reach high efficiency. The TEC concept is also mused to understand other biological motors and engines.