Membrane brush border

Sodium-dependent glucose cotransporters (SGLT) are located on small-intestine and kidney brush-border membranes. SGLT1, SGLT2, and SGLT3 are... 

In eukaryotes there is also evidence that Met(O) is actively transported. It has been reported that Met(O) is transported into purified rabbit intestinal and renal brush border membrane vesicles by a Met-dependent mechanism and accumulates inside the vesicles against a concentration gradient102. In both types of vesicles the rate of transport is increased with increasing concentrations of Na+ in the incubation medium. The effect of the Na+ is to increase the affinity of Met(O) for the carrier. Similar to that found in the bacterial system, the presence of Met and other amino acids in the incubation medium decreased the transport of Met(O). These results suggest that Met(O) is not transported by a unique carrier. 

The complex polymers in feedstuffs are broken down to the constituent building blocks by a sequential process. Hydrolysis of the polymers is initiated in the lumen of the GIT by enzymes and other secretions produced by the pancreas, stomach, intestine, liver and gall bladder, and other GIT tissues, and completed by another suite of enzymes associated with the brush border membrane (BBM) or intracellular organelles. Anti-nutrient phytochemicals can decrease the hydrolysis of feedstuffs, and thereby reduce nutrient availability, either by increasing the inherent resistance of the polymers to hydrolysis or by decreasing the activities or amounts of enzymes and other secretions produced by the GIT. 

Potential enzymes involved in anthocyanin metabolism — The lactase phlorizin hydrolase (LPH EC 3.2.1.108) present only in the small intestine on the outside of the brush border membrane and the cytosolic P-glucosidase (CBG EC 3.2.1.1) found in many tissues, particularly in liver, can catalyze the deglycosylation (or hydrolysis) of polyphenols. LPH may play a major role in polyphenol metabolism... 

Biochemical studies of plasma membrane Na /H exchangers have been directed at two major goals (1) identification of amino acids that are involved in the transport mechanism and (2) identification and characterization of the transport pro-tein(s). To date, most studies have been performed on the amiloride-resistant form of Na /H" exchanger that is present in apical or brush border membrane vesicles from mammalian kidney, probably because of the relative abundance of transport activity in this starting material. However, some studies have also been performed on the amiloride-sensitive isoform present in non-epithelial cells. 

Huot et al. [38] used affinity chromatography to identify and partially purify an amiloride-binding protein with characteristics of the renal brush border Na /H exchanger. The high-affinity amiloride analog A35 (5-A-(3-aminophenyl)amiloride) was coupled to Sepharose CL-4B through a triglycine spacer. Rabbit renal brush border membranes were solubilized with 0.6% Triton X-100, incubated with the... 

Subsequently, proteolytic fragments of the rabbit renal 25-kDa amiloride-binding protein were micro-sequenced and found to have high sequence homology with rat and human NAD(P)H quinone oxidoreductase. Indeed, enzymatic assays revealed that renal brush border membrane vesicles contain significant NADPH quinone oxidoreductase activity. Presumably NAD(P)H quinone oxidoreductase coincidentally binds amiloride analogs with the same rank order as the Na /H exchanger [39]. 

In a preliminary report, Ross et al. [40] used affinity chromatography to identify a putative bovine renal brush border Na /H exchanger. Brush border membranes were solubilized with Triton X-100 and chromatographed sequentially over lentil lectin Sepharose 4B and 5-(A-benzyl-iV-ethyl)amiloride coupled to epoxy-activated Sepharose 6B. The eluant contained 178- and 146-kDa proteins that were susceptible to Endo-F. Moreover, the eluants reacted on dot blot immunoassays with antisera to a 20-amino acid peptide of a human Na /H exchanger vide infra). The relationship between these proteins and the 66-kDa protein previously identified by the same investigators using amiloride photolabeling is presently unclear. 

Whereas the above studies have attempted to identify the Na /H exchanger in renal brush border membranes (a resistant-type), at least one study has reported possible identification of a sensitive-type transport protein [49]. The Na /H exchanger in lymphocytes (a sensitive-type) can be activated by either 12-0-tetradeca-noylphorbol 13-acetate (TPA) or osmotic shrinkage. TPA or osmotic shrinkage... 

In contrast to these results, Ross et al. [33] found that antisera against a 20-amino acid peptide (Ser-613-Arg-632) of the cytoplasmic domain of the human Na /H exchanger recognized a 66-kDa protein in immunoblots of bovine renal brush border membranes. Since the purity of these membranes was not reported it is possible that this result was due to contamination with basolateral membranes (although the molecular mass would still differ from the basolateral Na /H exchanger in LLC-... 

Temperature 20°C, equilibrium dialysis, small unilamellar vesicles (DOPC), 0.1 M KC1 [382]. Centrifugation method (15 min, 150,000 g), brush-border membrane vesicles [433]. 

CBB 1 — reconstituted brush-border membrane, rat (average of four studies). 

Alcorn, C. J. Simpson, R. J. Leahy, D. E. Peters, T. J., Partition and distribution coefficients of solutes and drugs in Brush Border membrane vesicles, Biochem. Pharmacol. 45, 1775-1782 (1993). 

Proulx, P., Structure-function relationships in intestinal brush border membranes, Biochim. Biophys. Acta 1071, 255-271 (1991). 

AC ADME ANS AUC BA/BE BBB BBM BBLM BCS BLM BSA CE CHO CMC CPC CPZ CTAB CV DA DOPC DPPC DPPH aminocoumarin absorption, distribution, metabolism, excretion anilinonaphthalenesulfonic acid area under the curve bioavailability-bioequivalence blood-brain barrier brush-border membrane brush-border lipid membrane biopharmaceutics classification system black lipid membrane bovine serum albumin capillary electrophoresis caroboxaldehyde critical micelle concentration centrifugal partition chromatography chlorpromazine cetyltrimethylammonium bromide cyclic votammetry dodecylcarboxylic acid dioleylphosphatidylcholine dipalmitoylphosphatidylcholine diphenylpicrylhydrazyl... 

Mucosal brush border membrane vesicles and basolateral membrane vesicles can be isolated to study solute uptake across specific enterocyte boundaries. These more isolated vesicle systems allow for investigation of solute transport across a particular membrane barrier and permit separation of membrane trans-... 

H Yuasa, D Fleisher, GL Amidon. Noncompetitive inhibition of cephradine uptake by enalapril in rabbit intestinal brush-border membrane vesicles An enalapril specific inhibitory binding site on the peptide carrier. J Pharmacol Exp Ther 269 1107-1111, 1994. 

N Piyapolrungroj, C Li, RL Pisoni, D Fleisher. Cimetidine transport in brush-border membrane vesicles from rat small intestine. J Pharmacol Exp Ther 289 346-353, 1999. 

The intestinal mucosal peptidases are distributed in the brush border and cytosol of the absorptive cell. There are, however, distinct differences between the brush border and cytosolic peptidases [75], The tetrapeptidase activity is associated exclusively with the brush border enzyme. Furthermore, brush border peptidases exhibit more activity against tripeptides than dipeptides, whereas the cytosolic enzymes show greater activity against dipeptides. Studies have demonstrated that more than 50% of dipeptidase activity was detected in the cytosol [76] and just 10% in the brush border membrane [77]. The brush border enzymes include... 

Aminopeptidase A is another brush border membrane enzyme which has been the subject of various studies [79,81,83-86], It has been found in the intestinal brush border membrane of humans, rabbits, rats, and pigs and is active against peptides with acidic amino acids at the amino terminus. Its activity against dipeptides is more limited. Shoaf et al., isolated three rat brush border aminopeptidases with distinct but somewhat overlapping substrate specificities. These enzymes had preference for dipeptides containing methionine, arginine, or aspartic acid and glycine. The optimal pH for activity of aminopeptidase was reported to be 7-8. 

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