Figure 3. ⁶³Ni²⁺ uptake of E281 mutants.

A. Mg²⁺ dose response curves for E281K, E281R, E281D single mutants and the E281K/K287E double mutant. B. Mg²⁺ dose response curves for E281A, E281L, E281N and E281Q single mutants. Each curve is normalized to maximal uptake for that strain in the absence of competing cation. The data are an average of at least 4 independent experiments done in triplicate. In a typical experiment, uptake ranged from 10,000 cpm for wild type to 1,500 cpm for E281N, over a background (10 mM Mg²⁺) of ~600 cpm. C. Maximal ⁶³Ni²⁺ uptake determined by incubating cells for 10 min with ~0.3 μCi ⁶³Ni²⁺ per tube with a total [Ni²⁺] of 125 μM. Uptake in the presence of 10 mM Mg²⁺ (~600 cpm) was taken as background and subtracted from total uptake to give net cpm uptake. The data are representative of at least three independent experiments done in triplicate.