title: Effect of hydrogen ion-gradient on carrier-mediated transport of glycylglycine across brush border membrane vesicles from rabbit small intestine.
abstract: Glycylglycine (Gly-Gly) transport across rabbit small intestinal brush border membrane vesicles was studied in the presence and absence of a Na+ gradient or a pH gradient. The transport was found to be entirely independent of Na+ but significantly stimulated by lowering extravesicular pH (pHo). The maximum stimulation was seen at pHo 5.5, where the uptake rate was about 2-times higher than the control value. FCCP, a protonophore, abolished the stimulating effect of low pHo, and low pHo conditions without a pH gradient did not stimulate the uptake rate. Overshoot uptake of Gly-Gly was observed when a pH gradient of 2 pH units was imposed across the vesicular membrane. Valinomycin-induced inside-negative K+ diffusion potential also had a stimulating effect on the uptake, and fluorescence measurements of vesicular suspensions containing diS-C3-(5) revealed the occurrence of depolarization of the vesicular membranes when Gly-Gly was added to the suspensions. Kinetic study showed that a pH gradient caused a decrease of Kt for Gly-Gly without affecting Vmax. All the data obtained indicate that Gly-Gly transport is independent of Na+, dependent on a H+ gradient, and electrogenic, suggesting the mechanism of cotransport with H+.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D004151:Dipeptides / Q000378:metabolism*; D006033:Glycylglycine / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007421:Intestine, Small / Q000378:metabolism / Q000648:ultrastructure*; D007700:Kinetics; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D013050:Spectrometry, Fluorescence
chemical_list: D002352:Carrier Proteins; D004151:Dipeptides; D006033:Glycylglycine; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D006859:Hydrogen; D012964:Sodium