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

Lactase and maltase, the predominant sugar hydrolases associated with the intestinal brush bordermembrane of the suckling rat, were purified essentially free of the other to near homogeneity (lactase at specific activity 23, maltase at specific activity 58), and their specific physiocochemical properties determined. Antisera prepared to each showed by immunodiffusion a single common precipitin line with pure enzyme and solubilized proteins of the brush border membrane. Brush border membranes were purified 26--35-fold from infant rat intestine. Membranes prepared from 10-day-old rats contained 32% protein, 43% lipid and 25% carbohydrate with lactase and maltase estimated to comprise in excess of 10% and 2%, respectively, of the membrane protein. Immunotitration curves of lactase and maltase showed equivalent antibody binding by the membrane-bound and free enzyme forms. Furthermore, antibody binding to one enzyme did not affect the immunotitration curve or the extractability (by papain or Triton X-100) of the other membrane-bound enzyme. It was concluded that the lactase and maltase molecules are attached singly on the external membrane surface in a spatially independent manner with their antigenic sites as freely available to antibody binding as exhibited by their papain-solubilized counterparts.
 ...
PMID:Sugar hydrolases of the infant rat intestine and their arrangement of the brush border membrane. 11 Mar 47

The arrangement of the sugar hydrolases, sucrase-isomaltase, maltase, and lactase on the microvillus membrane of rat intestine was investigated by immunological technique. The enzymes were purified essentially free of each other to near homogeneity and antisera of high specificity were obtained against each. Microvillus membranes were prepared routinely in high purity from rat intestine and contained an average 61% protein, 20% lipid, and 19% carbohydrate, with the sugar hydrolases comprising an estimated 20--25% of the membrane protein. The immunoreactivity of membrane-bound sucrase-isomaltase, maltase, and lactase was investigated with antisera demostrating specific reactivity to each, when tested in the presence of other membrane extractives. The membrane-bound enzymes were found in each case to combine with antibody in amounts equivalent to that required to effect precipitation of comparable units of the free enzymes from solution. Preloading membrane vesicles with antibodies to any two of the enzymes did not affect either the immunoreactivity or extractability (by papain or Triton X-100) of the third. The antibody-binding studies indicated an arrangement of these enzymes independent of each other on the membrane surface, in a manner allowing each to maintain a high degree of molecular freedom.
 ...
PMID:Sugar hydrolases and their arrangement on the rat intestinal microvillus membrane. 11 6

This study examines the effects of an enteropathogenic Escherichia coli on microvillar membrane proteins during organ culture of rabbit ileal explants. Explants maintained with enteropathogenic E coli showed brush border effacement affecting approximately 50% of enterocytes, and where enteropathogenic E coli were closely adherent to the enterocyte surface microvilli were apparently being shed as vesicles. The microvillar membrane enzymes alkaline phosphatase, aminopeptidase N and alpha-glucosidase were released into the culture medium during organ culture, and this process was significantly enhanced by enteropathogenic E coli. This increased loss of microvillar membrane enzymes into the culture medium was associated with decreased tissue activities of microvillar membrane enzymes in enteropathogenic E coli infected ileal explants compared with control. For aminopeptidase N in particular, however, total enzyme activities in the tissue plus culture medium were increased comparing enteropathogenic E coli with control, suggesting that there might be an increase in the rate of synthesis of certain microvillar membrane proteins. Reorientating sucrose density gradient centrifugation of culture medium showed that alkaline phosphatase, aminopeptidase N and alpha-glucosidase were predominantly associated with particles of peak modal density 1.19 g/ml in both groups, confirming that enteropathogenic E coli accelerate release of microvillar membrane enzymes as vesicles. Analytical fractionation of ileal explants showed that enteropathogenic E coli resulted in a loss of microvillar membrane enzyme activities from the main brush border peak of modal density 1.21 g/ml present in controls. The density of the remaining smaller and lighter peak increased from 1.19 g/ml to 1.23 g/ml after homogenisation in digitonin, confirming association of these proteins with cholesterol containing membranes and not endoplasmic reticulum. These findings suggest that enteropathogenic E. coli accelerate the normal shedding of microvillar membrane proteins as vesicles, and may stimulate a compensatory increase in microvillar membrane protein synthesis.
 ...
PMID:Effects of enteropathogenic Escherichia coli on microvillar membrane proteins during organ culture of rabbit intestinal mucosa. 135 65

Procedures have been validated for the investigation of the physical properties of canine microvillar membrane proteins by SDS-polyacrylamide gel electrophoresis. These have been used to examine mucosal samples from eight control dogs and from five dogs with naturally occurring exocrine pancreatic insufficiency (EPI) in order to evaluate the potential role of the pancreas in the normal turnover of microvillar membrane proteins in the dog. Gel scanning showed that the proportion of total membrane protein in bands corresponding to a molecular mass greater than 200 kDa was up to 20-times higher in dogs with EPI than in control dogs. In particular, a band of apparent molecular mass 218 kDa represented between 8 and 28% of membrane protein in all affected dogs, compared with only 0.5 to 1.8% in controls, and is most likely to contain single chains of both pro-maltase-glucoamylase and pro-sucrase-isomaltase. Incubation of microvillar membranes in vitro with either trypsin or canine pancreatic juice resulted in degradation of this high molecular mass band and a corresponding increase in the amount of protein in three bands representing molecular masses of 150, 133 and 106 kDa. In samples from control dogs aminopeptidase N was identified in the 133 kDa band by Western blotting and incubation with monospecific antiserum. These findings suggest that pancreatic enzymes play a major role in the normal post-translational processing of intestinal microvillar membrane proteins in the dog.
 ...
PMID:Investigation of the physical properties of dog intestinal microvillar membrane proteins by polyacrylamide gel electrophoresis: a comparison between normal dogs and dogs with exocrine pancreatic insufficiency. 340 88

The ability of eight stripping agents to solubilize five marker enzymes from rat renal brush border membranes isolated by three different preparative methods was examined. Protein and enzyme activities - alkaline phosphatase (APase), L-leucine aminopeptidase (LAPase), gamma-glutamyl transpeptidase (GGTase), gamma-glutamyl hydrolase (GGHase) and maltase - solubilized by the treatments were expressed as percent of total activity recovered in excess of control values. The relative enzyme activity and the solubilization factor were determined for each marker enzyme in every treated sample and the treatments with the eight agents compared. Trypsin treatment released > 80% of LAPase and < 10% of total membrane protein. Papain treatment released only 16--23% of total membrane protein but most of the enzyme activities except APase. Neuraminidase had no solubilizing effect. 4--10% of total membrane protein was solubilized by LiCl treatment but no marker enzyme activities were released. Less total membrane protein was released by treatment with proteolytic enzymes or LiCl than with the detergents Triton X-100, hexadecyltrimethylammonium bromide, sodium deoxycholate, and sodium dodecylsulfate. APase activity was the least readily solubilized. Correlating the degree of solubilization for five marker enzymes with the types of stripping agents used and with the appearance of the membrane surface when examined by electron microscopy led to the suggestion that LAPase, GGTase, GGHase and maltase molecules are part of an interwoven surface layer of membrane proteins which can be disrupted by transamidation and transesterification reactions. APase appears to be more strongly associated with the intact lipid matrix than the bulk of the membrane protein.
 ...
PMID:Ease of solubilization of five marker enzymes in three preparations of rat renal brush border membranes. 610 74

Bacteroides thetaiotaomicron, a gram-negative colonic anaerobe, can utilize three forms of starch: amylose, amylopectin, and pullulan. Previously, a neopullulanase, a pullulanase, and an alpha-glucosidase from B. thetaiotaomicron had been purified and characterized biochemically. The neopullulanase and alpha-glucosidase appeared to be the main enzymes involved in the breakdown of starch, because they were responsible for most of the starch-degrading activity detected in B. thetaiotaomicron cell extracts. To determine the importance of these enzymes in the starch utilization pathway, we cloned the genes encoding the neopullulanase and alpha-glucosidase. The gene encoding the neopullulanase (susA) was located upstream of the gene encoding the alpha-glucosidase (susB). Both genes were closely linked to another starch utilization gene, susC, which encodes a 115-kDa outer membrane protein that is essential for growth on starch. The gene encoding the pullulanase, pulI, was not located in this region in the chromosome. Disruption of the neopullulanase gene, susA, reduced the rate of growth on starch by about 30%. Elimination of susA in this strain allowed us to detect a low residual level of enzyme activity, which was localized to the membrane fraction. Previously, we had shown that a disruption in the pulI gene did not affect the rate of growth on pullulan. We have now shown that a double mutant, with a disruption in susA and in the pullulanase gene, pulI, was also able to grow on pullulan. Thus, there is at least one other starch-degrading enzyme besides the neopullulanase and the pullulanase. Disruption of the alpha-glucosidase gene, susB, reduced the rate of growth on starch only slightly. No residual alpha-glucosidase activity was detectable in extracts from this strain. Since this strain could still grow on maltose, maltotriose, and starch, there must be at least one other enzyme capable of degrading the small oligomers produced by the starch-degrading enzymes. Our results show that the starch utilization system of B. thetaiotaomicron is quite complex and contains a number of apparently redundant degradative enzymes.
 ...
PMID:Contribution of a neopullulanase, a pullulanase, and an alpha-glucosidase to growth of Bacteroides thetaiotaomicron on starch. 895 99

Calnexin, an abundant membrane protein, and its lumenal homolog calreticulin interact with nascent proteins in the endoplasmic reticulum. Because they have an affinity for monoglucosylated N-linked oligosaccharides which can be regenerated from the aglucosylated sugar, it has been speculated that this repeated oligosaccharide binding may play a role in nascent chain folding. To investigate the process, we have developed a novel assay system using microsomes freshly prepared from pulse labeled HepG2 cells. Unlike the previously described oxidative folding systems which required rabbit reticulocyte lysates, the oxidative folding of transferrin in isolated microsomes could be carried out in a defined solution. In this system, addition of a glucose donor, UDP-glucose, to the microsomes triggered glucosylation of transferrin and resulted in its cyclic interaction with calnexin and calreticulin. When the folding of transferrin in microsomes was analyzed, UDP-glucose enhanced the amount of folded transferrin and reduced the disulfide-linked aggregates. Analysis of transferrin folding in briefly heat-treated microsomes revealed that UDP-glucose was also effective in elimination of heat-induced misfolding. Incubation of the microsomes with an alpha-glucosidase inhibitor, castanospermine, prolonged the association of transferrin with the chaperones and prevented completion of folding and, importantly, aggregate formation, particularly in the calnexin complex. Accordingly, we demonstrate that repeated binding of the chaperones to the glucose of the transferrin sugar moiety prevents and corrects misfolding of the protein.
 ...
PMID:Promotion of transferrin folding by cyclic interactions with calnexin and calreticulin. 931 1

Structural and functional responses of the intestine to colostrum, milk replacer, oral electrolyte solution and food deprivation were examined during the first 6 h after birth in pigs. Total intestinal weight, surface area and mucosal mass were highest (P < 0.05) in pigs fed colostrum. The other diet groups did not differ, except that food-deprived pigs had lower surface area than the other groups. Feeding colostrum was associated with higher mucosal protein content (P < 0.05). Total intestinal brush border membrane protein content of pigs fed milk replacer, oral electrolyte solution and food-deprived pigs were 61, 44 and 56%, respectively, of those fed colostrum (P < 0.05). Pigs fed colostrum had higher total mucosal maltase activities than those that were food deprived, and total brush border membrane activities were higher than in those fed oral electrolyte solution. Total intestinal brush border membrane aminooligopeptidase activity was higher in pigs fed colostrum than in those given oral electrolyte solution or deprived of food, but total intestinal homogenate activities did not differ among groups. Diet influenced lactase activity only in the mid-region, and sucrase was not responsive to diet. Intestinal glucose transport capacity by intact intestinal tissues did not differ among diet groups. The ability of brush border membrane vesicles to actively accumulate glucose was lost when pigs were fed colostrum and milk replacer, but not when fed oral electrolyte solution or deprived of food. Our findings reveal how diet during the first 6 h after birth influences the structure and functional characteristics of the intestine. The responses vary between brush border membrane proteins and intestinal regions, and appear to differ from those described for older animals.
 ...
PMID:Diet influences development of the pig (Sus scrofa) intestine during the first 6 hours after birth. 968 48

The binary toxin (Bin) from Bacillus sphaericus crystals specifically binds to soluble midgut brush border membrane proteins from Culex pipiens larvae. A single 60 kDa midgut membrane protein is identified as the binding protein. This protein is anchored in the mosquito midgut membrane via a glycosyl-phosphatidylinositol (GPI) anchor, and is partially released by phosphatidylinositol specific-phospholipase C (PI-PLC). Fractionation of soluble proteins by anion exchange chromatography indicates that the binding protein does not co-elute with leucine aminopeptidase activity. After partial purification, the sequences of internal amino acid fragments of the 60 kDa protein were determined. The peptide sequences were compared with data in GenBank, and showed a very high degree of similarity with enzymes belonging to the alpha-amylase family. Further enzymatic investigation showed that the receptor of the Bin toxin in C. pipiens larval midgut may be an alpha-glucosidase.
 ...
PMID:Identification of the receptor for Bacillus sphaericus crystal toxin in the brush border membrane of the mosquito Culex pipiens (Diptera: Culicidae). 1045 23

We report that endoplasmic reticulum alpha-glucosidase inhibitors have antiviral effects on dengue (DEN) virus. We found that glucosidase inhibition strongly affects productive folding pathways of the envelope glycoproteins prM (the intracellular glycosylated precursor of M [membrane protein]) and E (envelope protein): the proper folding of prM bearing unprocessed N-linked oligosaccharide is inefficient, and this causes delayed formation of prME heterodimer. The complexes formed between incompletely folded prM and E appear to be unstable, leading to a nonproductive pathway. Inhibition of alpha-glucosidase-mediated N-linked oligosaccharide trimming may thus prevent the assembly of DEN virus by affecting the early stages of envelope glycoprotein processing.
 ...
PMID:Alpha-glucosidase inhibitors reduce dengue virus production by affecting the initial steps of virion morphogenesis in the endoplasmic reticulum. 1059 Jan 51


1 2 Next >>