Studies on the transport of anions and zwitterions of acidic amino acids in Streptomyces hydrogenans.

In Streptomyces hydrogenans, acidic amino acids are taken up either as anions by a specific transport system or as zwitterions via a nonspecific one. Variations in the zwitterion concentration caused by changes in pH influence the uptake and exchange diffusion by the nonspecific system. Differences in pH-optima for L-glutamate and L-aspartate transport are due to the different pK2-values of these amino acids. The anion transport by the specific system is accompanied by a short hyperpolarization of the membrane potential followed by a secondary influx of potassium ions into the cells.