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  • Title: Stoichiometry of Na+-succinate cotransport in renal brush-border membranes.
    Author: Wright SH, Kippen I, Wright EM.
    Journal: J Biol Chem; 1982 Feb 25; 257(4):1773-8. PubMed ID: 7056744.
    Abstract:
    The coupled transport of Na+ with succinate and citrate into rabbit renal brush-border membrane vesicles was studied. Initial rates of transport (J) were estimated from 1-s uptakes under well defined transmembrane conditions (membrane potential, pH, ionic composition). A Na+ gradient increased J up to 700 times compared to Na+ replacement with sorbitol. J was a sigmoid function of increasing Na+ concentration; the kinetic interaction of Na+ with the succinate-citrate transport system was described by the equation: J = Jmax/(1 + (Ks/[Na]))3. Assuming that the Na+ interaction involves equivalent, noninteracting binding sites, these results indicate that 3 Na+ ions are translocated/molecule of organic substrate. Consistent with the latter observation was the direct demonstration of a stoichiometric coupling between simultaneously determined fluxes of 22Na+ and 14C-labeled substrates. In excess of 2 Na+ ions were transported/molecule of organic substrate. These results explain the electrogenicity of the transport of succinate and citrate as evidenced by the response of J to K+ diffusion potentials and the effects of transport on the fluorescence of a potential-sensitive cyanine dye.
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