title: Characteristics of D-galactose transport systems by luminal membrane vesicles from rabbit kidney.
abstract: The characteristics of renal transport of D-galactose by luminal membrane vesicles from either whole cortex, pars recta or pars convoluta of rabbit proximal tubule were investigated by a spectrophotometric method using a potential-sensitive carbocyanine dye. Uptake of D-galactose by luminal membrane vesicles prepared from whole cortex was carried out by an Na+-dependent and electrogenic process. Eadie-Hofstee analysis of saturation-kinetic data suggested the presence of multiple transport systems in vesicles from whole cortex for the uptake of D-galactose. Tubular localization of the transport systems was studied by the use of vesicles derived from pars recta and pars convoluta. In pars recta, Na+-dependent transport of D-galactose and D-glucose occurred by means of a high-affinity system (half-saturation: D-galactose, 0.15 +/- 0.02 mM; D-glucose, 0.13 +/- 0.02 mM). These results indicated that the "carrier' responsible for the uptake of these hexoses does not discriminate between the steric position of the C-4 hydroxyl group of these two isomers. This is further confirmed by competition experiments, which showed that D-galactose and D-glucose are taken up by the same and equal affinity transport system by these vesicle preparations. Uptake of D-galactose and D-glucose by luminal membrane vesicles isolated from pars convoluta was mediated by a low-affinity common transport system (half-saturation: D-galactose, 15 +/- 2 mM; D-glucose, 2.5 +/- 0.5 mM). These findings strongly suggested that the "carrier' involved in the transport of monosaccharides in vesicles from pars convoluta is specific for the steric position of the C-4 hydroxyl group of these sugars and presumably interacts only with D-glucose at normal physiological concentration.
mesh_terms: D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D005690:Galactose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D066298:In Vitro Techniques; D007684:Kidney Tubules / Q000378:metabolism*; D007700:Kinetics; D009004:Monosaccharide Transport Proteins / Q000032:analysis; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D009004:Monosaccharide Transport Proteins; D012964:Sodium; D005947:Glucose; D011188:Potassium; D005690:Galactose