Transport mechanisms of a glycoside, p-nitrophenyl-beta-D-glucopyranoside, across rat small intestinal brush-border membranes.
We examined the mechanism of p-nitrophenyl-beta-d-glucopyranoside (p-NP-beta-d-Glc) transport in brush-border membrane vesicles from rat small intestine. The initial uptake rate showed an overshoot phenomenon in the presence of an inwardly directed sodium-ion concentration gradient. The overshoot disappeared when the sodium-ion concentration gradient was replaced with a potassium ion concentration gradient. d-Glucose and p-NP-beta-D-Glc analogues inhibited the uptake, whereas uridine, leucine and disaccharide did not. Data on the concentration dependence of p-NP-beta-D-Glc uptake indicated that two carrier-mediated systems are involved. The uptake via the high-affinity site required an inwardly directed sodium-ion concentration gradient, while the uptake via the low-affinity site proceeded such a gradient. D-Glucose competitively inhibited the initial uptake of p-NP-beta-D-Glc via the high-affinity site with a Ki value of 301 microM. The p-NP-beta-D-Glc is transported in the small intestine via both the same carrier-mediated transport system that takes up D-glucose and a distinct low-affinity carrier-mediated transport system.
Ohnishi
T
T
Department of Biopharmaceutics, School of Pharmacy, Tokyo University of Pharmacy and Life Science, 1432-1 Horinouchi, Hachioji, Tokyo 192-03, Japan.
Higashi
S
S
Mizuma
T
T
Awazu
S
S
D000469:Alkaline Phosphatase / Q000032:analysis; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive; D001692:Biological Transport; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D005960:Glucosides / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000648:ultrastructure*; D007421:Intestine, Small / Q000166:cytology / Q000378:metabolism; D008297:Male; D008871:Microvilli / Q000378:metabolism; D009994:Osmolar Concentration; D051381:Rats; D017208:Rats, Wistar; D013347:Subcellular Fractions / Q000201:enzymology / Q000378:metabolism
D005960:Glucosides; C025193:4-nitrophenyl beta-D-glucoside; D000469:Alkaline Phosphatase; D005947:Glucose