Mechanisms of Energy Coupling to the Transport of Amino Acids by Staphylococcus aureus

Abstract

We have studied the effect of artifically imposed transmembrane pH gradients on the uptake of amino acids by Staphylococcus aureus. In high potassium medium, cells treated with valinomycin and tetrachlorosalicylanilide and at Donnan equilibrium, were found to accumulate glutamate. In low potassium medium, addition of acid to the extracellular environment was found to stimulate the uptake of glutamate and aspartate, to induce partial lysine efflux, and to cause a small and transient isoleucine uptake. In conjunction with earlier data from this laboratory (1973), it is concluded that the basic, neutral and acidic amino acids behave, respectively, as cationic, uncharged and anionic sub-strates, accumulating in Staphylococcus aureus in response to (a) the membrane potential, inside negative, (b) the total protonmotive force, and (c) the transmembrane pH gradient, inside alkaline.