Examination of the substrate stoichiometry of the intestinal Na + /phosphate cotransporter

摘要: The substrate stoichiometry of the intestinal Na+/phosphate cotransporter was examined using two measures Na+-dependent phosphate uptake: initial rates uptake with [32P] and phosphate-induced membrane depolarization potential-sensitive dye diSC3(5). Isotopic electrogenic electroneutral uptake, while uptake. Using these Na-dependent three parameters were compared: affinity; phenylglyoxal sensitivity labeling; inhibiton by mono- di-fluorophosphates. cotransport found to have similar Na+ activations (apparentK 0.5's 28 25mm), apparentK m 's for (100 410 μm), andK 0.5's inhibition (70 90 μm) isotopic phosphate, depolarization, respectively. Only difluorophosphate inhibited below 1mm at pH 7.4. Difluorophosphate also protected a 130-kDa polypeptide from FITC-PG labeling in presence apparentK 0.5 200 μm; andK 0.5 protection against polypeptide. These results indicate that is 7.4, H2PO 4 − transport-competent species, an excellent candidate cotransporter.