title: Critical carboxyl group(s) in Na+-dependent cotransporters of the intestinal brush-border membrane.
abstract: We have previously provided functional evidence for a role of carboxyl group(s) in the mechanism of coupling of Na+ and D-glucose fluxes by the small-intestinal cotransporter(s) (Kessler, M. and Semenza, G. (1983) J. Membrane Biol. 76, 27-56). We present here a study on the inactivation of the Na+-dependent transport systems, but not of the Na+-independent ones, in the small-intestinal brush-border membrane, by hydrophobic carbodiimides. Although marginal or insignificant protection by the substrates or by Na+ was observed, the parallelism between Na+-dependence and inactivation by these carbodiimides strongly indicates the role of carboxyl group(s) previously indicated. Contrary to the carboxyl group identified by Turner [1986) J. Biol. Chem. 261, 1041-1047) in the sugar binding site of the renal Na+/D-glucose cotransporter, the carboxyl group(s) studied here probably occur elsewhere in the cotransporter molecule.
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D004024:Dicyclohexylcarbodiimide / Q000378:metabolism; D004226:Dithioerythritol / Q000494:pharmacology; D005632:Fructose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D019811:Hydroxylamine; D006898:Hydroxylamines / Q000494:pharmacology; D007421:Intestine, Small / Q000378:metabolism*; D007700:Kinetics; D008627:Mercuric Chloride / Q000494:pharmacology; D008871:Microvilli / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D000596:Amino Acids; D002352:Carrier Proteins; D006898:Hydroxylamines; D009004:Monosaccharide Transport Proteins; D019811:Hydroxylamine; D005632:Fructose; D004024:Dicyclohexylcarbodiimide; D008627:Mercuric Chloride; D005680:gamma-Aminobutyric Acid; D004226:Dithioerythritol; D012964:Sodium; D005947:Glucose