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)

Chicken intestinal sucrase-isomaltase and maltase-glucoamylase have been isolated in their intact form by detergent solubilization and characterized as to their subunit composition and mode of anchoring in the brush-border membrane. Both are heterodimeric enzyme complexes composed of two subunits each of approximately 140 and 130 kDa. Contrary to the mammalian sucrase-isomaltase, chicken isomaltase was identified as the smaller of the two subunits. As was shown by hydrophobic labeling, only one of the two subunits in each heterodimer is anchored in the bilayer, the smaller 130 kDa isomaltase subunit of the sucrase-isomaltase complex, and the larger 140 kDa subunit of the maltase-glucoamylase complex. Both preparations contain a high-molecular weight polypeptide of approximately 250 kDa which in the case of sucrase-isomaltase could be identified by peptide mapping as a single-chain precursor not (yet) proteolytically processed to the final heterodimer. These first data on the mode of membrane anchoring of non-mammalian glycosidases indicate that they are synthesized, inserted into the membrane, and processed in ways similar to the mammalian enzymes. The fundamental unity between avian and mammalian sucrase-isomaltases suggests that the partial gene duplication of an ancestral isomaltase gene and the subsequent mutation of one of the active sites resulting in pro-sucrase-isomaltase has occurred prior to the separation of mammals from reptiles, i.e. more than 300 million years ago.
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PMID:The mode of anchoring and precursor forms of sucrase-isomaltase and maltase-glucoamylase in chicken intestinal brush-border membrane. Phylogenetic implications. 309 40

The alpha-glucosidase inhibitor acarbose has been successfully used in diabetic patients to decrease the postprandial rise in blood glucose. The aim of the present experiments was to investigate the fate and effects of acarbose along the small intestine using a slow-marker perfusion technique. In 8 healthy volunteers, jejunal and ileal loads of acarbose, glucose, and total carbohydrates were determined following a liquid, 400-kcal formula meal containing either 200 mg of acarbose or placebo. Preprandial and postprandial plasma concentrations of glucose and several polypeptide hormones were determined. Recovery of acarbose during 4 h was 65% +/- 9% (mean +/- SEM) of ingested dose in the ileum but 94% +/- 9% in the jejunum, indicating that the compound was neither degraded nor absorbed by the intestine to a major degree. After acarbose administration, ileal loads of glucose and total carbohydrates were considerably higher, whereas postprandial plasma concentrations of glucose, insulin, and gastric inhibitory polypeptide were lower when compared with placebo. The retardation of carbohydrate digestion to be inferred from these findings is confirmed by significantly elevated plasma concentrations of enteroglucagon after acarbose administration compared with placebo administration.
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PMID:Fate and effects of the alpha-glucosidase inhibitor acarbose in humans. An intestinal slow-marker perfusion study. 328 63

The NH2-terminal sequence (25 residues) of amphiphilic single polypeptide chain maltase-glucoamylase (EC 3.2.1.20) was determined by gas-phase sequencing. The result indicates that the NH2-terminal segment anchors the enzyme to the microvillar membrane. The single-chain form and the proteolytically processed two-chain form have two distinct active sites differing in heat stability. However, both sites are sensitive to chonduritol B-epoxide and have similar substrate specificity. The amphiphilic single-chain maltase-glucoamylase and the amphiphilic proteolytically processed form were inserted into liposomes and studied by electron microscopy. The results showed that the enzyme is predominantly present as a homodimeric complex in the membrane.
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PMID:Pig intestinal microvillar maltase-glucoamylase. Structure and membrane insertion. 352 55

The molecular basis for charge heterogeneity in human hepatic alpha-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) was determined by analysis of the carbohydrate and polypeptide components of the enzyme. Only small remnants of high mannose chains that contained neither sialic acid nor mannose 6-phosphate were detected in the carbohydrate structure. Four enzymatically active forms of alpha-glucosidase separated by chromatofocusing were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and were found to contain different polypeptides. The absence of charged residues in oligosaccharide chains and variability in the polypeptide subunits of the charge forms of hepatic alpha-glucosidase suggest that charge heterogeneity results from differences in the protein structure of the charge forms. The pattern of differences in the polypeptide subunits suggests that the charge forms for hepatic alpha-glucosidase may be the product of proteolysis.
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PMID:The molecular basis for charge heterogeneity in human acid alpha-glucosidase. 388 74

A large amount of lysosomal acid hydrolases was released into the medium by Tetrahymena pyriformis strain W during growth. An extracellular lysosomal acid alpha-glucosidase has been purified 500-fold with a 41% yield to homogeneity, as judged by polyacrylamide gel electrophoresis. It was found to be a glycoprotein and to consist of a single 110,000-dalton polypeptide chain. The carbohydrate content of the alpha-glucosidase was equivalent to 2.8% of the total protein content, and the oligosaccharide moiety was composed of mannose and N-acetylglucosamine in a molar ratio of 6.7:2. The optimal pHs for hydrolysis of maltose and p-nitrophenyl-alpha-glucopyranoside, maltose, isomaltose, and glycogen were 1.1 mM, 2.5 mM, 33.0 mM, and 18.5 mg/ml, respectively. This purified enzyme appears to have alpha-1,6-glucosidase as well as alpha-1,4-glucosidase activity. Turanose has a noncompetitive inhibitory effect on the hydrolysis of maltose. The antibody raised against Tetrahymena acid alpha-glucosidase inhibited the hydrolysis of all substrates tested. These properties of Tetrahymena acid alpha-glucosidase were found to be similar to those of the human liver lysosomal alpha-glucosidase.
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PMID:Purification and characterization of lysosomal alpha-glucosidase secreted by eukaryote Tetrahymena. 392 1

Structural changes have been studied during the life cycles of three glycosidases: sucrase-isomaltase (EC 3.2.48-10), lactase-phlorizin hydrolase (EC 3.2.1.23-62), maltase-glucoamylase (EC 3.2.1.20); and three peptidases: aminopeptidase A (EC 3.4.11.7), aminopeptidase N (EC 3.4.11.2) and dipeptidyl peptidase IV (EC 3.4.14.5). The final forms of the enzymes can be divided into at least two groups: the sucrase-isomaltase type, characterized as dimers, which are asymmetric in their hydrophilic parts, have two types of active site and anchor only on one subunit; and the aminopeptidase N type, characterized as dimers, which are symmetric in their hydrophilic part, have only one type of active site and anchor on both subunits. These enzymes are likely to be synthesized on rough endoplasmic reticulum and simultaneously glycosylated into endoglycosidase H-sensitive forms. They are later reglycosylated to endoglycosidase H-resistant forms, which have relative molecular masses similar to the final forms. Enzymes of the sucrase-isomaltase type seem to be synthesized with a polypeptide-chain length corresponding to the sum of both subunits, whereas enzymes of the aminopeptidase N type seem to be synthesized with a polypeptide-chain length corresponding to the constituent subunits themselves. Not much is known about the catabolism of these enzymes. The enzyme activities and the amounts of enzyme protein decrease at the top of the villi, probably due to release into the lumen. The subunits of aminopeptidase N are cleaved by pancreatic proteases to smaller peptides, and sucrase-isomaltase may lose its sucrase polypeptide, while both enzymes remain bound to the membrane.
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PMID:Structure of microvillar enzymes in different phases of their life cycles. 613 6

A two-step procedure is described for the isolation of lysosomal alpha-glucosidase from human urine. In the second step, affinity chromatography on Sephadex G-100, two fractions with acid alpha-glucosidase activity were obtained. Fraction I contained alpha-glucosidase of Mr 109000, whereas fraction II contained components of Mr 76000 and 70000. alpha-Glucosidase in fraction I had an Mr similar to that of the precursor of alpha-glucosidase detected in the medium of fibroblasts after labelling with [14C]leucine. The components in fraction II had Mr identical to those of the mature forms of alpha-glucosidase found in placenta or cultured human skin fibroblasts. alpha-Glucosidase in fraction I contained mannose 6-phosphate (3.5 mol/mol polypeptide). No mannose 6-phosphate was present in the components in fraction II. Fraction I, but not fraction II, was avidly endocytosed by alpha-glucosidase-deficient cultured human skin fibroblasts. Endocytosis of fraction I was inhibited by mannose 6-phosphate. The pH optimum and Km values for p-nitrophenyl alpha-glucoside, maltose and glycogen of fractions I and II alpha-glucosidase were almost identical. However, the activity with glycogen relative to that of either p-nitrophenyl alpha-glucoside or maltose was lower in fraction I than in fraction II. It is concluded that fraction I consists of the precursor form of alpha-glucosidase and fraction II of the mature forms of the enzyme. The importance of urine as a source of precursors of lysosomal enzymes is discussed.
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PMID:Isolation and characterization of a precursor form of lysosomal alpha-glucosidase from human urine. 636 53

Acid alpha-glucosidase has been purified from human placenta to a specific activity of approximately 6800, (4-methylumbelliferyl-alpha-D-glucoside as a substrate) or 55,400 mumol g-1 min-1 (glycogen or maltose as substrate). The purified enzyme gives rise to multiple protein bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), i.e., a major doublet of 82K and 69K , a minor doublet of 25K and 21K , and a faint band of 100K. All of the molecular weight species stained as glycoproteins with an intensity apparently proportional to their protein content, and were present in enzyme from individuals homozygous for the allozyme alpha-Glu 1. Isoelectric focusing revealed only enzymatically active proteins which, when analysed by SDS-PAGE, gave rise to multiple molecular weight species. Chromatography of I125-labeled, purified enzyme on Bio-Gel P-100 revealed only a radiolabeled, high-molecular-weight species which corresponded with enzyme activity. These findings suggest that, in the native state, the mature enzyme exists as a high-molecular-weight species, which is dissociable in SDS to several low-molecular-weight species. These results are consistent with reports that a 100K primary product of translation is post-translationally modified to yield polypeptides of lower molecular weights, and that all of the molecular species are absent in cells genetically deficient for acid alpha-glucosidase. The possibility that the low-molecular-weight (20- 25K ) protein bands in SDS-gels corresponded to a previously reported low-molecular-weight species generated by treatment with guanidine-HCl was investigated. The I125-labeled, purified acid maltase was dissociated by guanidine into two equal peaks of approximately 64K and 28K molecular weight. Surprisingly, both peaks, when analyzed on SDS-gels, yielded identical and equally intensely staining bands of 64K molecular weight. These results suggest that the mature acid alpha-glucosidase is made up of polypeptides which are bonded in the native state by at least two different types of interaction, one type which is dissociable in SDS and one type which is dissociable in guanidine but not in SDS. The nature and possible function of the 25K polypeptide generated only by guanidine-HCl remains to be determined.
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PMID:Further studies of the structure of human placental acid alpha-glucosidase. 642 17

The enzyme responsible for all of the isomaltase activity and much of the maltase activity in the small intestine of the Californian sea lion (Zalophus californianus) was isolated by detergent solubilization of the brush-border membrane, followed by immunoadsorption chromatography using antibodies directed against rabbit sucrase-isomaltase. In 0.1% Triton X-100, sea lion isomaltase occurs as a monomer of Mr = 245,000 and is composed of a single polypeptide chain. As judged from the stoichiometry of the covalent binding of the affinity label, conduritol-B-epoxide, this polypeptide chain carries two enzymatically active sites; they are apparently identical and do not show either positive or negative cooperativity. In addition to cross-reacting immunologically with rabbit sucrase-isomaltase, sea lion isomaltase has similar overall enzymatic properties, with the exception of not hydrolyzing sucrose. The Alaskan fur seal (Collarhinus ursinus) has a two-active site isomaltase; however, in contrast to the sea lion, this animal is endowed with a small but significant sucrase activity. Along with (fully active) pro-sucrase-isomaltase, sea lion isomaltase is one of the very few examples of enzymes with more than one active site on a single polypeptide chain acting "in parallel" (rather than "in series"). Furthermore, this enzyme triggers some interesting questions on the phylogenetical pedigree of small intestinal sucrase-isomaltase.
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PMID:A two-active site one-polypeptide enzyme: the isomaltase from sea lion small intestinal brush-border membrane. Its possible phylogenetic relationship with sucrase-isomaltase. 671 26

The methods of centrifugal elutriation, two-dimensional gel electrophoresis, and dual isotopic labeling were applied to the study and identification of a number of purified yeast proteins. The location of polypeptide spots corresponding to specific proteins was determined on two-dimensional gels. A dual-label method was used to determine the rates of synthesis through the cell cycle of the identified proteins as well as to confirm the results of previous studies from our laboratory on unidentified proteins. The identified proteins, and the more generally defined phosphorylated, heat shock, and heat stroke proteins were found to follow the general pattern of exponential increase in rate of synthesis through the cell cycle. In addition, colorimetric enzyme activity assays were used to examine the catabolic enzyme alpha-glucosidase (EC 3.2.1.20). Both the activity and synthesis of alpha-glucosidase were found to be nonperiodic with respect to the cell cycle. These data contrast with earlier reports of periodicity, which employed induction and selection synchrony to study enzyme expression through the yeast cell cycle.
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PMID:Synthesis of specific identified, phosphorylated, heat shock, and heat stroke proteins through the cell cycle of Saccharomyces cerevisiae. 705 Jun 67


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