Plasmodium use digestive vacuoles (DV) to digest hemoglobin and heme from red blood cells into fuel sources for their life cycle. The DV is the site where host proteins are degraded by the parasite and then the peptide pieces are exported into the Plasmodium c

Plasmodium use digestive vacuoles (DV) to digest hemoglobin and heme from red blood cells into fuel sources for their life cycle. The DV is the site where host proteins are degraded by the parasite and then the peptide pieces are exported into the Plasmodium cytosol for use in biosynthesis. Plasmodium falciparum chloroquine resistance transporter, PfCRT, is a transporter in this DV membrane and its original function was unknown until recently. Researchers digested hemoglobin into peptide fragments and then tested the effect of these fragments on PfCRT function. VF-6-2 is one of these fragments of hemoglobin and apparently a natural substrate of PfCRT. Chloroquine, for which the transporter was originally named, is a substrate only of mutant transporters. One mutant PfCRT, for instance, has K76T in its substrate binding site and thus a significantly lower Km for chloroquine, inspiring the original name of the transporter, because of its importance for drug resistance in malaria patients.

The cytosolic pH of Plasmodium is 7.1. Suppose PfCRT is a secondary active symporter using protons to drive VF-6-2 efflux from the digestive vacuole, DV. Suppose the membrane potential across the DV membrane is 50mV, inside positive. VF-6-2 has a 3nM concentration inside the DV and a 56nM concentration in the cytosol. What pH must the P-type ATPase establish inside of a digestive vacuole in order to allow PfCRT to spontaneously transport 1 VF-6-2 out of the DV with 1 H+ at 37°C?