Properties of the Glutamate Transport System in Escherichia coli

Abstract

The properties of the glutamate transport system in two glutamate-utilizing mutants of Escherichia coli K-12 were investigated. Growth in the presence of glutamate enhanced the capacity of the bacteria for glutamate uptake. Accumulation of glutamate was found to be an energy-linked highly temperature-dependent process. Nonlinear double reciprocal plots of uptake were obtained in the absence of an exogenous energy source and in the presence of glucose or glycerol. Addition of γ-aminobutyrate, succinate, ketoglutarate, or aspartate accelerated glutamate uptake and brought about “normalization” of its kinetics. Straight-line kinetics of uptake was also observed when succinate served as the source of energy. Under these conditions, aspartate and α-ketoglutarate inhibited glutamate uptake in a noncompetitive fashion, whereas γ-aminobutyrate activated the system. A number of other amino acids were found to act as “noncompetitive” inhibitors. d -glutamate and some derivatives of glutamate with an unsubstituted α-carboxylic and α-amino group inhibited l -glutamate uptake in a strictly competitive fashion. An allosteric permease model, consistent with all of these findings, is proposed.