FIG. 7.

Expulsion of accumulated [¹⁴C]TMG-6-P (A) and [¹⁴C]2-DG-6-P (B) in the L. lactis wild-type strain MG5267 and the ptsH1 mutant LlG101. Cells grown in the presence of 0.5% lactose or 0.5% glucose were preloaded with [¹⁴C]TMG or [¹⁴C]2-DG, respectively. The amount of labeled sugar remaining inside the cells during a 5-min (for TMG) or 15-min (for 2-DG) incubation period at 37°C in the presence or absence of glucose was determined by withdrawing aliquots at the indicated time intervals and analyzing them by the rapid-filtration method (37). Squares, no sugar added; circles, 10 mM glucose added at time zero. S46AO and wtO, no glucose added to cells preloaded with [¹⁴C]2-DG-6-P. For the latter samples, aliquots were withdrawn only at the beginning and at the end of the experiments. Leakage levels of [¹⁴C]2-DG-6-P from the cells were found to be nearly identical for the wild-type and the ptsH1 mutant strains, explaining why the lines for the two strains coincide.