The kinetics of dihydrostreptomycin uptake in Pseudomonas putida membrane vesicles: absence of inhibition by cations

Abstract

Dihydrostreptomycin was taken up in isolated cytoplasmic membrane vesicles of Pseudomonas putida by an active transport mechanism. Saturation kinetics were observed with an apparent Km and Vmax of 15 mM and 50 nmol/min/mg of protein respectively. The evidence suggested that the observed kinetics was that of the energy-dependent phase I component of dihydrostreptomycin uptake. Neither magnesium nor the polyamine, spermine, inhibited dihydrostreptomycin transport. Thus, the inhibition of aminoglycoside uptake in intact cells of Gram-negative bacteria and the increase in the minimal inhibitory concentration in the presence of multivalent cations and polyamines were interpreted to be effects that take place at the outer membrane level.