FIG. 1.

Activation of glycine betaine transport by hyperosmotic conditions. L. lactis IL1403 or MG1363 cells were grown semianaerobically at 29°C in CDM (without proline), pH 6.5, plus 25 mM glucose and 500 mM KCl, after which they were washed and resuspended in 50 mM KP_i, pH 6.5. (A) Prior to the initiation of transport, IL1403 cells were pre-energized for 5 min with 10 mM glucose. Uptake of [¹⁴C]glycine betaine (1.25 mM, final concentration) was assayed in 50 mM KP_i, pH 6.5, with (●, ■) or without (○) 500 mM KCl. The reaction was stopped with LiCl at 500 (●) or 100 (■, ○) mM. (B) Effect of hyperosmotic conditions on the uptake of alanine and glutamate. Experimental conditions and symbols are the same as for panel A, except that the uptake of [¹⁴C]alanine (solid lines) and [¹⁴C]glutamate (dotted lines) was assayed at 625 μM. (C) Effect of intracellular proline on the uptake of glycine betaine. Prior to the initiation of transport, MG1363 cells were pre-energized for 45 min with 10 mM glucose with (▴, ▵) or without (●, ○) 1.25 mM proline. In a parallel experiment, the proline was added at time zero, that is, simultaneously with [¹⁴C]glycine betaine (■, □). Uptake of [¹⁴C]glycine betaine was assayed in 50 mM KP_i, pH 6.5, containing chloramphenicol at 50 μg/ml with (closed symbols) or without (open symbols) 500 mM KCl. The reactions were stopped with 500 (closed symbols) or 100 (open symbols) mM LiCl; this was followed by rapid filtration and washing of the filters.