On the mechanism of translocation of dihydrostreptomycin across the bacterial cytoplasmic membrane

Abstract

This review examines two mechanisms, the channel and the uniport, proposed to explain the rapid, energy-dependent (EDP-II) phase of transport of dihydrostreptomycin (and streptomycin) across the bacterial cytoplasmic membrane. Bioenergetic and kinetic predictions are made from these two mechanisms and compared with available experimental data. Both the above mechanisms would be expected to lead to reversible transport kinetics, and to observable uptake of dihydrostreptomycin by respiring cytoplasmic membrane vesicles. However, transport is kinetically irreversible and is not observed in membrane vesicles (although the membrane vesicle findings need further confirmation), so the author rejects the proposed channel and uniport mechanisms. A possible mechanism of dihydrostreptomycin transport that would be consistent with the above experimental data, would be one in which a chemical reaction occurred as an obligatory part of the translocation cycle. Such a mechanism could be classified as primary translocation. The author emphasizes that this hypothesis is put forward to stimulate further experimental testing; it is not proposed to be a definitive explanation of the mechanism of energy-dependent dihydrostreptomycin transport.