FIG. 5.

Acu1 and Acu2 transport K⁺ and Na⁺ in U. maydis as shown by results for K⁺ and Na⁺ uptake in the wild-type strain, Δacu1 and Δacu2 single mutants, and Δacu1 Δacu2 double mutant of U. maydis. In the single mutants the experiments were started at 60 and 10 μM (inset) to show the regulation of the enzyme by the internal cations and its very low K_m. Experiments, as described in the legend to Fig. 4 for measurement of Na⁺ (closed circles) and K⁺ (open triangles), were performed at the following cell densities (dry weights): wild-type strain, 0.49 mg ml⁻¹ for both the K⁺ and Na⁺ experiments; Δacu1 Δacu2, 0.53 mg ml⁻¹ for the K⁺ experiment and 0.94 mg ml⁻¹ for the Na⁺ experiment; Δacu1 main panel, 0.58 mg ml⁻¹ for both the K⁺ and Na⁺ experiments; Δacu1 inset, 0.30 mg ml⁻¹ for both the K⁺ and Na⁺ experiments; Δacu2 main panel, 0.51 mg ml⁻¹ for both the K⁺ and Na⁺ experiments; and Δacu2 inset, 0.60 mg ml⁻¹ for both the K⁺ and Na⁺ experiments.