Fig. 2.

Lactose active transport. A & B). Initial rates of lactose transport for E. coli T184 (ΔlacZY) or HB101 (lacZ⁺Y⁻) intact cells, respectively. C). Time course of lactose accumulation for E. coli T184 intact cells. D). Active transport by RSO membrane vesicles prepared from E. coli T184 expressing wild-type or D240E LacY. E. coli T184 or HB101 intact cells containing wild type(λ), mutant D240E (σ) or empty vector (ν) were adjusted to an OD₄₂₀ of 10.0 (0.7 mg protein/ml). Transport was carried out with [¹⁴C]lactose (10 mCi/mmol) at a final concentration of 0.4 mM (solid line). The intracellular lactose concentration is plotted as a function of time. Lactose transport in RSO membrane vesicles in Panel D was assayed at a protein concentration of 3.5 mg/ml in the presence of 20 mM ascorbate/0.2 mM phenazine methosulfate under oxygen with [¹⁴C]lactose at a final concentration of 0.4 mM (10 mCi/mmol; solid line) or 4.0 mM (2.5 mCi/mmol; dashed line) as described in Experimental Procedures. The intravesicular lactose concentration after correction for RSO vesicles transformed with empty vector is plotted as a function of time.