RECTIFIED BROWNIAN-MOVEMENT IN MOLECULAR AND CELL BIOLOGY

A unified model is presented for rectified Brownian movement as the me chanism for a variety of putatively chemomechanical energy conversions in molecular and cell biology. The model is established by a detailed analysis of ubiquinone transport in electron transport chains and of allosteric conformation changes in proteins. It is applied to P-type A TPase ion transporters and to a variety of rotary arm enzyme complexes . It provides a basis for the dynamics of actin-myosin cross-bridges i n muscle fibers. In this model, metabolic free energy does no work dir ectly, but instead biases boundary conditions for thermal diffusion. A ll work is done by thermal energy, which is harnessed at the expense o f metabolic free energy through the establishment of the asymmetric bo undary conditions.