Microvillar membrane

AJ Kenny, S Maronx. Topology of microvillar membrane hydrolases of kidney and intestine. Physiol Rev 62 91-128, 1982. 

Rocha, J. and Munn, E.A. (1997) P150, a protective glycoprotein complex of the microvillar membrane of Haemonchus contortus. Conference Abstract from Parasitic Helminths - from Genomes to Vaccines, Edinburgh, UK, 6-9 September 1997. 

Smith, S.K., Pettit, D., Newlands, G.F.J., Redmond, D.L., Skuce, P.J., Knox, D.P. and Smith, W.D. (1999) Further immunisation and biochemical studies with a protective antigen complex from the microvillar membrane of the intestine of Haemonchus contortus. Parasite Immunology 21, 187—199. 

That derivatization may increase rather than decrease peptidase-catalyzed degradation is illustrated with aspartame (6.79, R = MeO), the C-terminal methyl ester of the dipeptide Asp-Phe. The metabolism of this artificial sweetener was compared to that of the underivatized dipeptide (6.79, R = H) and of the corresponding amide Asp-Phe-NH2 (6.79, R = NH2) in microvillar membranes obtained from human duodenum, jejunum, and ileum [189]. The activities monitored were clearly those of peptidases as shown by the effects of inhibitors. Whereas the peptide bond in Asp-Phe and Asp-Phe-NH2 was hydrolyzed at a comparable rate, that in aspartame was hydrolyzed approximately twice as fast. This is an interesting and favorable situation, given that aspartame is expected to be degraded once it has elicited its effect in the buccal cavity. 

Hedeager-Sorensen, S., and A.J. Kenny. 1985. Proteins of the kidney microvillar membrane. Purification and properties of carboxypeptidase P from pig kidneys. Biochem J 229 251. 

K. Barnes, J. Ingram, A. J. Kenny, Proteins of the kidney microvillar membrane. Structural and immunochemical properties of rat endopeptidase-2 and its immu-nohistochemical location in tissues of rat and mouse, Biochem J 264 335-346 (1989). 

For the selective labeling of the acetylcholine receptor Saitoh et al. used the covalently bound non-competitive blocker 5-azido- H-trimethioquin. Asymmetric labeling of the proteins in the kidney microvillar membrane by lactoperoxidase-catalysed radioiodination and by photolysis of 3,5-di- I-4-azidobenzenesulphonate is a new approach which may be applied to the topological investigation of ojmplex membranes... 

Although only CaBP mRNA is known to increase in response to vitamin D, other vitamin D-dependent changes occur in the intestinal epithelium, including increases in activity of alkaline phosphatase, calcium ATPase, adenylate cyclase, and RNA polymerase. In response to vitamin D, several brush-border membrane proteins increase in concentration as does a calcium-binding complex. Non-cAMP-dependent phosphorylation of a brush-border membrane protein, increased synthesis and turnover of microvillar membrane phospholipids, and effects on mitochondria, Golgi membranes, and intracellular membrane vesicles are observed. Increased transport of Ca " " across the basolateral membrane may be produced by... 

Pregnancy. Serotransferrin is involved in the process of iron transfer to the foetus by a placental receptor-mediated mechanism. The three glycovariants of serotransferrin and their binding to human syncytiotrophoblast microvillar membranes have been studied by Leger et al. [108]. The results obtained by these authors and others [243,244] showed that in the serum of pregnant women, especially in the last... 

Aminopeptidase P is present in the microvillar membranes of pig and human kidney, and membrane-bound forms are also present in rat intestine and lung, bovine lung and guinea pig kidney. Soluble forms occur in rat serum and brain, human platelets and guinea pig serum, and it has also been characterized from human leukocytes. It is one of a group of cell-surface proteins anchored in the lipid bilayer by glycolyl-phosphatidylinositol (see Membrane lipids). 

Microvillar membranes are prepared from freshly delivered human placentae... 

Histochemical techniques at the level both of the electron microscope and the light microscope depict alkaline phosphatase being located on the microvillar membranes of the absorbing epithelial cells of the intestinal mucosa (Hugon and Borgers, 1966), of the proximal convoluted tubules and of the trophoblast syncitium. The glycocalyx has become the focus of... 

From diis, Moog concludes that the hydrocortisone permits the onset of differentiation of the microvillar membrane of the 10-day epithelium... 

With regard to hydrolases on the microvillar membranes, Moog (1971a,b) suggests that they may each have a morphological identity, either in the continuum of the membrane as for alkaline phosphatase or in die knobs as for sucrase and leucyl naphfliylamidase and be subjected to the wear and tear of intestinal activity raflier than to the normal processes of enzyme degradation. 

Not only are phosphohydrolases membrane components, but a variety of other enzymes such as glycosidases have been shown to share the same location. For example, the microvillar membranes of the absorbing epithelial cells of the intestine contain sucrase, maltase, and leucine amino-peptidase the basal infolding membranes of mouse renal epithelial cells exhibit both acid phosphatase and yS-glucuronidase. 

Based on experimental data and theoretical considerations[25-27], the suggested role of the bile salt micelle is to overcome the "resistance" of the UWL to lipid diffusion across the microvillar membrane. There is, however, little evidence to suggest that this "resistance" is differentially affected by trihydroxy bile salt-containing micelles, as opposed to micelles containing dihydroxy bile salts. Thus, although an (UWL) may limit sterol diffusion at the mucosal cell surface, there does not appear to be a major specifictiy of a unique bile salt structure in modifying the resistance of this barrier. 

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