FIG. 3.

Dependence of the initial rate of lactose uptake on the lactose concentration. Cells of L. plantarum ATCC 14917 were grown on CDM containing 30% (wt/vol) lactose (Lac) plus 0.5% glucose (Glu) or CDM containing 0.5% lactose plus 0.5% glucose, washed, and resuspended in potassium phosphate (pH 6.5) to a final protein concentration of 1.5 mg/ml. After 6 min of preenergization with 10 mM glucose, uptake was initiated at time zero by the addition of [¹⁴C]lactose, and the initial uptake rates were determined after 30 s of uptake. The inset shows the initial rate of lactose uptake at low lactose concentrations.