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

The data shown are for glucose-6-phosphate ac­cumulation 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 dra­matically 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 accumu­lation 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).