Figure 2.

Biochemical properties of zinc uptake in yeast expressing the ZIP1, ZIP2, or ZIP3 genes. zrt1 zrt2 (ZHY3) transformants expressing ZIP1, ZIP2, or ZIP3 were grown to exponential phase (≈5 × 10⁶ cells/ml) in synthetic-defined medium and assayed for zinc uptake with ⁶⁵Zn. Because of their different pH optima for uptake activity, the ZIP1 and ZIP3 activities were assayed at pH 4.7, and ZIP2 activity was assayed at pH 6.0. (A–C) Time and temperature dependence of zinc accumulation assayed with 10 μM (ZIP1, ZIP3) or 1 μM ⁶⁵Zn (ZIP2) at 0°C (open symbols) and at 30°C (closed symbols). (D–F) Concentration dependence of zinc uptake was determined by measuring zinc accumulation for 5 min over a range of substrate concentrations. Each point in A–F represents the mean of two experiments each performed in duplicate, and the error bars represent ±1 SD. (G–I) Inhibition of ZIP-dependent uptake in yeast by other metals. Cells were assayed for zinc uptake rate with 10 μM (ZIP1, ZIP3) or 1 μM (ZIP2) ⁶⁵Zn in the absence (−) or presence of 10-fold excess of the chloride salts of the indicated metal ions. Each value represents the mean of four replicates. The asterisks indicate significant differences from control values (P < 0.05) as determined by one-way ANOVA followed by Scheffe’s test.