Figure 4.

Effects of inhibitors and ionophores on the uptake of CE-GS, DNP-GS, and CSG. The conditions for ATP-dependent uptake were as in Figure 2 except uptake was terminated after 30 min. All of the conjugates were present at a concentration of 50 μm. Where indicated, bafilomycin A₁, nigericin, valinomycin, and vanadate were added at concentrations of 0.4, 2, 2, and 200 μm, respectively. The bafilomycin A₁ stock solution was made up in dimethyl sulfoxide; the valinomycin and nigericin stock solutions were made up in ethanol. Control experiments confirmed that neither dimethyl sulfoxide nor ethanol at the concentrations at which they were added to the uptake medium (0.004% [v/v] and 0.04% [v/v], respectively) affected uptake. Uptake is expressed as a percentage of the uptake by controls to which no inhibitors or ionophores had been added. The control activities were 52.5, 7.7, and 13.4 nmol mg⁻¹ protein for CE-GS, DNP-GS, and CSG, respectively. The values shown are the means of duplicate measurements from a representative experiment.