Figure 2.

SO₄ ²⁻ efflux by mutant AE1 polypeptides. (A) Extracellular SO₄ ²⁻ supported ³⁵SO₄ ²⁻ efflux from AE1 E699Q-expressing oocytes (lower two traces) but not from oocytes expressing wt AE1 or AE1 mutants with T, K, G, or R in place of E699 (upper cluster of 8 traces). Extracellular condition shown above x axis. DIDS was added in the continued presence of SO₄ ²⁻. Representative of 3 similar experiments performed 4–5 d after cRNA injection. Each trace represents a single oocyte. (B) SO₄ ²⁻/Cl⁻ exchange mediated by AE1 E699Q was 70% faster than SO₄ ²⁻/SO₄ ²⁻ exchange. DIDS inhibited efflux in the continued presence of Cl⁻. The two uppermost traces show efflux from water-injected oocytes. The six traces below show efflux from AE1 E699Q-expressing oocytes. (C) Bar graph of the data in B, (n) for each condition above bars. *P < 0.02.