FIGURE 3.

Histidine/histamine exchange is controlled by the pmf. Cells of L. lactis NZ9000 ΔlysQ expressing HdcP were loaded with 5 mm histamine and resuspended to an A₆₀₀ of 2 in 200 mm KPi (pH 6.0) buffer. Fifteen seconds before addition of 1.5 μm ¹⁴C-histidine, either no further additions were made (●), or 5 μm valinomycin (△), 5 μm nigericin (▾), 5 μm valinomycin, and 5 μm nigericin (○), 25 μm CCCP (■), and 10 mm glucose (□) was added to the cells.