title: Role of carboxyl and sulfhydryl residues on rabbit small intestinal brush-border membrane Na(+)-glucose cotransporter.
abstract: The role of sulfhydryl (SH) and carboxylic acid residues in Na(+)-dependent glucose uptake, Na(+)-dependent phlorizin binding, and substrate exchange by the rabbit small intestinal brush-border membrane (BBM) Na(+)-glucose cotransporter was examined in sodium dodecyl sulfate-BBM vesicles. The sulfhydryl reagent p-chloromercuribenzoate (PCMB) inhibited all three measures of cotransporter function in a dithiothreitol-sensitive manner with similar K0.5 values (concn of PCMB resulting in 50% inhibition). PCMB sulfonate had no effect on Na(+)-glucose cotransporter function < 250 microM. The carboxylic acid reagent 1-ethyl-3-(4-azonia-4,4-dimethylpentyl)carbodiimide no effect on Na(+)-glucose cotransporter function. N,N'-dicyclohexylcarbodiimide (DCCD) inhibited all three measures of cotransporter function with similar K0.5 values for inhibition. Inhibition by DCCD did not require addition of a nucleophile. In contrast, PCMB-pretreated cotransporter was insensitive to DCCD in the absence of added nucleophile with respect to substrate transport (Na(+)-dependent glucose uptake) but not Na(+)-dependent phlorizin binding. These results indicate an intravesicular or lipophilic environment for both the PCMB-reactive SH residue and the DCCD-reactive carboxylic acid residues, suggesting that a SH residue may act as an endogenous nucleophile for interaction of DCCD with the Na(+)-glucose cotransporter and suggesting that different carboxylic acid residues may be involved in Na(+)-dependent glucose uptake and Na(+)-dependent phlorizin binding.
authors.affiliation: Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550.
authors.forename: B E
authors.initials: BE
authors.lastname: Peerce
authors.forename: M
authors.initials: M
authors.lastname: Cedilote
authors.forename: R D
authors.initials: RD
authors.lastname: Clarke
mesh_terms: D000818:Animals; D002264:Carboxylic Acids / Q000494:pharmacology*; D002729:Chloromercuribenzoates / Q000494:pharmacology; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D004350:Drug Residues / Q000494:pharmacology; D007421:Intestine, Small / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011817:Rabbits; D013439:Sulfhydryl Reagents / Q000494:pharmacology*
chemical_list: D002264:Carboxylic Acids; D002729:Chloromercuribenzoates; D009004:Monosaccharide Transport Proteins; D013439:Sulfhydryl Reagents; D004024:Dicyclohexylcarbodiimide