V-type ATPases are capable of establishing a steep pH gradient across the membranes in which they are present.

6. A. V-type ATPases are capable of establishing a steep pH gradient across the membranes in which they are present.  However, establishment of a steep pH gradient can also produce a steep electrical gradient across that membrane as protons carry a positive charge.  In biological situations, V-type ATPases are often found in the same membranes as ion channels, which work to alleviate the electrical potential across the membrane and thus maximize the pH gradient.  You have a sample of a vacuole preparation from a plant source that is capable of establishing an intravacuolar (luminal) pH of 3.5 when incubated at 25oC in a pH 7.5 buffer system containing 3 mM MgATP and 50 mM KCl.  However, when another sample of the same vacuole preparation is incubated in the same buffer system except that the KCl is replaced by 25 mM K2SO4, the intravacuolar pH established is much higher and not much different from that of the pH 7.5 buffer system.  Provide an explanation for these results.