title: Sugar uptake by intestinal basolateral membrane vesicles.
abstract: A high yield of membrane vesicles was prepared from the basolateral surface of rat intestinal cells using an N2 cavitation bomb and density gradient centrifugation. The membranes were enriched 10-fold and were free of significatn contamination by brush border membranes and mitochondria. The rate of D-E114C]glucose and L-E13H]glucose uptake into the vesicle was measured using a rapid filtration technique. D-Glucose equilibrated within the vesicles with a half-time 1/25th that for L-glucose. The stereospecific uptake exhibited saturation kinetics with a Km of approx. 44 mM and a V of approx. 110 nmol . mg-1 min-1 at 10 degrees C. The activation energy for the process was 14 kcal . mol-1 below 15 degrees C and it approached 3 kcal . mol-1 above 22 degrees C. Carrier-mediated uptake was eliminated in the presence of 1 mM HgCl2 and 0.5 mM phloretin. The rate of transport was unaffected by the absence or presence of sodium concentration gradients. Competition studies demonstrated that all sugars with the D-glucose pyranose ring chair conformation shared the transport system, and that, with the possible exception of the -OH group at carbon No. 1, there were no specific requirements for an equatorial -OH group at any position in the pyranose ring. In the case of alpha-methyl-D-glucoside its inability to share the D-glucose transport system may be due to steric hindrance posed by the -OCH3 group rather than by a specific requirement for a free hydroxyl group at the position in the ring. It is concluded that sugars are transported across the basolateral membrane of the intestinal epithelium by a facilitated diffusion system reminiscent of that in human red blood cells.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002250:Carbon Radioisotopes; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D007421:Intestine, Small / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000201:enzymology; D009005:Monosaccharides / Q000494:pharmacology; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013393:Sucrase / Q000032:analysis; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D009005:Monosaccharides; D014316:Tritium; D013393:Sucrase; D000254:Sodium-Potassium-Exchanging ATPase; D005947:Glucose