FIG. 2.

Dependence of glycine betaine uptake on the internal proline concentration. Cells of L. plantarum ATCC 14917 were grown on CDM without proline containing 0.8 M KCl. The cells were washed and resuspended in 50 mM potassium phosphate (pH 6.5) plus 50 μg of chloramphenicol per ml to a final protein concentration of 0.18 mg/ml. After 40 min of preenergization with 10 mM glucose, uptake was initiated at time zero by the addition of 1.3 mM [¹⁴C]glycine betaine (no add) or 1.3 mM [¹⁴C]glycine betaine plus 1.3 mM unlabeled proline [Pro(0)]. Alternatively, the cells were preenergized for 40 min with 10 mM glucose plus 1.3 mM unlabeled proline, and uptake was initiated at time zero by the addition of 1.3 mM [¹⁴C]glycine betaine [Pro(−40)]. The uptake was assayed without (open symbols) or with (closed symbols) 0.8 M KCl (final concentration) added together with the glucose.