Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.20 (alpha-glucosidase)
 4,237 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two membrane proteins, maltase and gp330 (the pathogenic antigen of Heymann nephritis), present in the proximal tubule brush border have recently been independently purified and found to be large glycoproteins of similar molecular weight (Mr = approximately 300,000) by SDS PAGE. To determine the relationship between the two, monoclonal antibodies raised against the purified proteins were used for comparative immunochemical analyses and immunocytochemical localization. When a detergent extract of [35S]methionine-labeled rat renal cortex was used for immunoprecipitation with monoclonal antimaltase IgG, a single band of approximately 300 kdaltons was precipitated, whereas a single 330-kdalton band was precipitated with monoclonal anti-gp330 IgG. Monoclonal antimaltase (gp300) IgG also immunoprecipitated maltase activity from solubilized renal maltase preparations, whereas monoclonal anti-gp330 IgG failed to do so. When cyanogen bromide-generated peptide maps of the two proteins were compared, there were many similar peptides, but some differences. When maltase and gp330 were localized by indirect immunofluorescence and by indirect immunoperoxidase and immunogold techniques at the electron microscope level, they were found to be differently distributed in the brush border of the initial (S1 and S2) segments of the proximal tubule: maltase was concentrated (approximately 90%) on the microvilli, and gp330 was concentrated (approximately 90%) in the clathrin-coated apical invaginations located at the base of the microvilli. We conclude that maltase (gp300) and the Heymann nephritis antigen (gp330) are structurally related membrane glycoproteins with a distinctive distribution in the proximal tubule brush border which may serve as markers for the microvillar and coated microdomains, respectively, of the apical plasmalemma.
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PMID:Microdomains of distinctive glycoprotein composition in the kidney proximal tubule brush border. 637 Oct 23

The nature of the cytoplasmic coat present on the apical invaginations of the kidney proximal tubule cell was investigated by immuneoverlay and immunocytochemistry of renal brush borders with anticlathrin antibodies. When kidney cortex was prepared for electron microscopy using methods that enhance visualization of clathrin coats, the apical invaginations at the base of the brush border microvilli were seen to be backed by a nearly continuous coating which resembles but is more extensive than the lattice-like clathrin coats found around brain coated vesicles. When isolated brush border fractions were prepared under conditions that preserve the coats, separated by SDS PAGE, and transferred to nitrocellulose, the presence of clathrin heavy and light chains was detected by immuneoverlay using two different affinity-purified anticlathrin IgGs--one that we prepared, which detects only the clathrin light chains, and the other, prepared by Louvard et al. ( Louvard , D., C. Morris, G. Warren, K. Stanley, F. Winkler , and H. Reggio , 1983, EMBO [Eur. Mol. Biol. Organ.] J., 2:1655-1664), which detects both the heavy and light chains. As viewed by light microscopy (immunofluorescence or immunoperoxidase), staining with both anticlathrins was concentrated at the base of the proximal tubule microvilli. Immunoelectron microscopic localizations carried out on brush border fractions (using peroxidase and gold conjugates) demonstrated specific binding of anticlathrin IgGs to the lattice-like cytoplasmic coat. When brush border fractions were reacted with monoclonal antibodies prepared against gp330 and maltase, proteins that serve as markers for the membrane of the apical invaginations and microvilli, respectively ( Kerjaschki , D., L. Noronha - Blob , B. Sacktor , and M. G. Farquhar , 1984, J. Cell Biol., 98:1505-1513), the two proteins retained their restrictive distribution in the brush border. The findings demonstrate (a) that the cytoplasmic coat of the proximal tubule intermicrovillar apical invaginations is composed of clathrin heavy and light chains, and (b) that the differential distribution of proteins in these two brush border microdomains is maintained in appropriately prepared brush border fractions.
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PMID:Presence of an extensive clathrin coat on the apical plasmalemma of the rat kidney proximal tubule cell. 637 81

Renal tissue sections from 178 patients, whose kidneys were either normal or altered by various conditions such as hydronephrosis, interstitial nephropathies, chronic graft rejection, renal cancer etc., were investigated by computer-assisted histophotometry. We used enzyme histochemical and immunologic methods to measure kidneys suffering from various urological diseases quantitatively. Through this procedure, we were able to obtain information that allowed us to determine the degree of alteration in the metabolic state of tubular epithelial cells. The tissue activities of the following enzymes of the proximal tubule were investigated: alanine aminopeptidase (AAP), alkaline phosphatase (AP) and maltase (Ma) as membrane-bound markers, and beta-glucuronidase (beta-Gl) as a lysosomal marker. In addition, AAP and gamma-glutamyltranspeptidase (GGTP) were measured by immunofluorescent microscopy after having added specific anti-enzyme antibodies to the tissue sections. Compared to normal kidneys, quantitative enzyme histograms of diseased kidneys revealed a significant decrease in marker protein concentration of the tubule. The decline in tissue enzyme activities of AP, AAP, Ma and beta-Gl was accompanied by a significant decrease of enzyme concentrations as measured by the immuno histological method. This was especially true in cases with kidney cancer and in kidney tissues adjacent to infiltration adenocarcinoma. Morphological analyses of alterations were generally improved by enzymatic and/or immunologic histophotometry.
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PMID:Quantitative enzymatic and immunologic computer-assisted histophotometry of human kidney tissue following neoplastic and other clinically significant alterations. 687 27

Left kidneys of rats were made ischemic for 25 minutes and proximal tubule brush border alterations studied in the S1 and S2 segments. Scanning electron microscopy revealed that brush border microvilli became unstable, fused with one another, and were interiorized into proximal tubule cytoplasm soon after reflow of blood following ischemia. Rapid regeneration followed; scanning electron microscopy showed that regeneration occurred in a fashion whereby clusters of microvilli in flower-like configurations were extruded from the cell interior toward the surface. Such unique patterns of microvillus formation have not been reported before. Activity of the brush border enzymes, alkaline phosphatase and maltase, were not significantly depressed throughout the cycle of brush border loss and regeneration. Likewise, there were no alterations in the activity of beta-glucuronidase, a lysosomal enzyme. Alkaline phosphatase cytochemistry showed that microvillus membranes that were interiorized into the cell cytoplasm retained enzyme activity on their surfaces during the early period of brush border loss as well as during regeneration. These results strongly suggest that in reversibly injured proximal tubule cells regeneration of the brush border occurs primarily by a process of recycling of damaged, previously incorporated membrane. The nature of the initial membrane damage and the mechanism of recycling remain unknown.
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PMID:Mechanism of proximal tubule brush border loss and regeneration following mild renal ischemia. 730 Feb 48

The endosomal pathway of the rat renal cortex was labeled by intravenous infusion of fluorescent dextran small enough to cross the glomerular ultrafiltration barrier and be taken up by luminal endocytosis in the proximal tubule. Clathrin-coated vesicles (CCV) were isolated from the rat renal cortex utilizing discontinuous sucrose density gradients and negative lectin selection. More than 99 +/- 1% (n = 4) of the isolated vesicles contain entrapped fluorescein dextran when analyzed by small-particle flow cytometry techniques. Similarly, flow cytometry analysis demonstrates brisk H(+)-adenosinetriphosphatase activity in virtually all the vesicles. Western blot analysis of the vesicle proteins with a polyclonal anticlathrin antibody stains bands consistent with clathrin and adaptins. When the isolated vesicles are decoated by exposure to 0.5 M tris(hydroxymethyl)aminomethane, the proteins released match the molecular weights of the proteins identified on Western blot analysis. Flow cytometry demonstration of brush border enzymes in > 99% of the vesicles and Western blot identification of maltase suggests both that these vesicles are of apical origin and that apical enzymes traffic into endosomal elements. Additionally, two glycoproteins detectable in this fraction on Western blot analysis and flow cytometry immunocytochemistry are derived from intermicrovillar clefts traffic into the endosomal pathway. Hence, apical proteins traffic into a population of CCV isolated from the rat renal cortex.
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PMID:Trafficking of apical proteins into clathrin-coated vesicles isolated from rat renal cortex. 818 87

To reinvestigate the "hydrolase-related transport" concept, neutral alpha-D-glucosidase, a membrane-bound disaccharidase of renal proximal tubule, was first purified from brush-border membranes and then asymmetrically reincorporated into egg phosphatidylcholine vesicles. Proteolytic treatments and immunotitration studies demonstrated that this enzyme was integrated in native and artificial membrane vesicles with a similar topology. The uptake of free glucose and glucose produced by maltose hydrolysis was studied using 1) proteoliposomes containing integrated neutral alpha-D-glucosidase, in combination with other membrane proteins, and 2) proteoliposomes containing only the other membrane proteins but incubated in a medium containing neutral alpha-D-glucosidase in its hydrophilic form. No modification was observed in the uptake of free D-glucose or D-glucose produced by maltose hydrolysis, regardless of enzyme localization. In contrast to previous findings on the hydrolase-related transport concept, these results rule out any participation of neutral alpha-D-glucosidase in the transport of free glucose or glucose produced by maltose hydrolysis. Hydrolytic activity and transmembrane transport appear to be two independent and sequential steps.
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PMID:Renal neutral alpha-D-glucosidase has no role in transport of D-glucose derived from maltose hydrolysis. 957 82

Immune complex tubulointerstitial nephritis due to antibodies to brush border antigens of the proximal tubule has been demonstrated experimentally and rarely in humans. Our patient developed ESRD and early recurrence after transplantation. IgG and C3 deposits were conspicuous in the tubular basement membrane of proximal tubules, corresponding to deposits observed by electron microscopy. Rare subepithelial deposits were found in the glomeruli. The patient had no evidence of SLE and had normal complement levels. Serum samples from the patient reacted with the brush border of normal human kidney, in contrast with the negative results with 20 control serum samples. Preliminary characterization of the brush border target antigen excluded megalin, CD10, and maltase. We postulate that antibodies to brush border antigens cause direct epithelial injury, accumulate in the tubular basement membrane, and elicit an interstitial inflammatory response.
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PMID:Immune Complex Tubulointerstitial Nephritis Due to Autoantibodies to the Proximal Tubule Brush Border. 2633 28


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