Glycine uptake in Escherichia coli. I. Glycine uptake by whole cells of Escherichia coli W+ and a D-serine-resistant.

These experiments were designed to investigate the defect in amino acid uptake in a D-serine-resistant mutant (WS) of Escherichia coli W that is deficient in the uptake of glycine. Under conditions in which there is insignificant metabolism of glycine (i.e. 0” under nitrogen), the wild type took up significant amounts of glycine, whereas the WS mutant did not equilibrate with the external glycine pool. The initial rate of glycine uptake by the wild type as a function of the external glycine concentration was nonlinear, increasing rapidly from 1.3 X 10u5 M to 2.6 X 10d4 M and decreasing at concentrations above 2.6 X 10M4 M. The WS mutant took up glycine at an initial rate which was 3to 4-fold less than that of the wild type. The defect could not be attributed to an increased exit process in the WS mutant. Although the WS mutant was able to take up glycine from low external concentrations to the same extent as the wild type, it did so at a much slower rate. Membrane preparations from the wild type cells were found to take up glycine, and membrane preparations from the WS mutant were found to exhibit the defect in glycine uptake. It is concluded that the defect manifested by this D-serineresistant mutant of E. coli is in the passage of glycine through the cell membrane.