Effect of high substrate concentrations on active transport parameters.

A general model is described to account for the observation that steady-state accumulation ratios (mainly of non-electrolytes) decrease with increasing solute concentration, frequently reaching values of less than unity. Three variants of the model are treated, all of them including the assumption that the immediate supply of the source of energy is limited and its local concentration is appreciably reduced by its interaction with the transport system. Consequences of this assumption for the kinetic parameters of the initial rate of transport are analyzed and compared with experimental data.