Figure 5.  Transport systems coupled to DpH at pH 5.5.

The data shown are for glucose-6-phosphate ac苞umulation by RSO vesicles containing this transport system.  Similar profiles are observed for lactate, glucuronate and gluconate.  At pH 5.5, accumulation of each of these acids is stimulated dra衫atically by valinomycin.  However, at pH 7.5, accumulation is actually better than at pH 5.5 (not shown).  Moreover, while valinomycin stimulates at pH 5.5, the ionophore effectively inhibits accumu衍ation at pH 7.5.  In addition, nigericin inhibits relatively mildly at pH 5.5 and not at all at pH 7.5.  Conclusion - at pH 5.5, accumulation of these substrates is driven primarily by DpH, but at pH 7.5, accumulation is driven by DY (i.e., the mechanism becomes electrogenic at high pH).