Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.26 (invertase)
 4,927 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The separation by polyacrylamide gel electrophoresis and subsequent enzymatic analysis of the components of the guinea pig intestinal brush border membrane revealed the presence of three enzyme complexes: maltase-glucoamylase, maltase-sucrase-glucoamylase and maltase-sucrase. Additional bands possessing lactase, trehalase and alkaline phosphatase activity were identified but no phlorizin hydrolase or palatinase was detectable. After exposure to strong dissociating conditions the bands possessing enzymatic activity were either absent or greatly reduced in intensity.
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PMID:Glycosidases of the guinea pig brush border membrane. 86 Dec 25

Lactase-phlorizin hydrolase was isolated by immunoadsorption chromatography from rabbit brush-border membrane vesicles. Inactivation of the enzyme with [3H]conduritol-B-epoxide, a covalent active site-directed inhibitor, labeled glutamates at positions 1271 and 1747. Glu1271 was assigned to lactase, Glu1747 to phlorizin hydrolase activity. In contrast, the nucleophiles in the active sites of sucrase-isomaltase are aspartates (Asp505 and Asp1394). Asp505 is a part of the isomaltase active site and is localized on the larger subunit, which carries the membrane anchor also, while Asp1394 is a part of the active of sucrase. Alignment of these 2 nucleophilic Glu residues in lactase-phlorizin hydrolase and of their flanking regions with published sequences of several other beta-glycosidases allows the classification of the configuration retaining glycosidases into two major families: the "Asp" and the "Glu" glycosidases, depending on the carboxylate presumed to interact with the putative oxocarbonium ion in the transition state. We offer some predictions as to the Glu acting as the nucleophile in the active site of some glycosidases. By hydrophobic photolabeling, the membrane-spanning domain of lactase-phlorizin hydrolase was directly localized in the carboxyl-terminal region thus confirming this enzyme as a monotopic type I protein (i.e. with Nout-Cin orientation) of the brush-border membranes. A simplified version of the Me2+ precipitation method to efficiently and simply prepare brush-border membrane vesicles is also reported.
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PMID:Location of the two catalytic sites in intestinal lactase-phlorizin hydrolase. Comparison with sucrase-isomaltase and with other glycosidases, the membrane anchor of lactase-phlorizin hydrolase. 138 57

In the rat, starvation lowers jejunal sucrase activity and increases or has no effect upon jejunal lactase activity. The mechanism by which starvation influences these intrinsic microvillus proteins remains unclear. Jejunal sucrase and lactase activities were studied during starvation or refeeding after a three-day fast. Using polyclonal monospecific antibodies, sucrase-isomaltase (SI) and lactase-phlorizin hydrolase (LPH) protein contents were measured in parallel to determine changes in enzyme activation. Sucrase activity and SI protein fell after two and three days of fasting and rose during refeeding. In contrast, lactase activity and jejunal LPH content increased after starvation and decreased after refeeding for 48 hr. For both enzymes, changes in catalytic activity and protein content occurred in parallel. [3H]Leucine incorporation studies in vivo showed more labeling of immunoprecipitable LPH than SI during starvation, but refeeding induced relatively more labeling of SI than of LPH. Therefore, starvation and refeeding produce opposing effects upon jejunal lactase and sucrase activities by modulating LPH and SI protein production and not by modifying enzyme activation.
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PMID:Effects of starvation and refeeding on jejunal disaccharidase activity. 158 86

We have described the methods used for studying the biosynthesis and the post-translational processing of sucrase-isomaltase (SI), lactase-phlorizin hydrolase (LPH) and maltase-glucoamylase (MGA) in human small intestinal mucosa. Our results are discussed in the context of findings by other researchers. A surprising finding coming out of all these studies is that SI, LPH and MGA are structurally quite different. SI and LPH are both synthesized as large molecular weight precursors which are proteolytically processed to the mature enzymes. In the case of SI, this processing occurs after insertion of the precursor into the brush border membrane and is catalysed by pancreatic proteases; the mature form consists of the two subunits sucrase and isomaltase, the latter containing an N-terminal peptide anchor. Proteolytic processing of the LPH-precursor occurs intracellularly, yielding a mature enzyme in the form of a two active site polypeptide which is anchored via a C-terminal peptide. The role of the large cleaved propolypeptide of LPH is not yet known. MGA is the largest of the three disaccharidases, having a molecular weight of greater than 300 kDa. No proteolytic processing seems to be taking place during biogenesis of MGA in human mucosa, and the mode of attachment to the membrane is unknown at present. The application of the methods described to the investigation of congenital sucrase-isomaltase deficiency (CSID) and lactase restriction in adults is presented and differences between CSID and LPH restriction are discussed.
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PMID:Molecular aspects of disaccharidase deficiencies. 211 33

Adult rats when fed a high carbohydrate diet of 70% sucrose or glucose for 24 h following a 4-day fast showed increased concentrations of intestinal sucrase-isomaltase (EC 3.2.1.48, EC 3.2.1.10) and maltase-glucoamylase (EC 3.2.1.20) but not lactase-phlorizin hydrolase (EC 3.2.1.23, EC 3.2.1.62). The concentration increases of these enzymes were accompanied by corresponding acceleration of their synthesis rates. Contrary to earlier studies by others, suggesting that upper villus cells in the fasted intestine are unresponsive to stimulation of sucrase activity by refeeding a high-sucrose diet, the concentration increases of both sucrase-isomaltase and maltase-glucoamylase were seen to occur in cells all along the length of the villus column. The earlier studies differed from the present study by basing enzyme assays relative to protein rather than the DNA content of villus cell fractions. We have shown that villus cells increase their protein content severalfold while migrating to villus tip, providing the basis for the difference between earlier and the present findings. Further evidence that stimulation of sucrase-isomaltase and maltase-glucoamylase by high carbohydrate is not restricted to the crypt and lower villus region was obtained by the finding that their synthesis rates appeared to be equally stimulated along the length of the villus column.
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PMID:Dietary CHO and stimulation of carbohydrases along villus column of fasted rat jejunum. 249 55

Lactase-phlorizin hydrolase, a small intestinal disaccharidase, has been considered mainly an enzyme important only for the hydrolysis of lactose. After weaning in most mammals lactase-specific activity falls markedly, and, functionally, adult mammals are considered to be lactase deficient. However, the persistence of low levels of lactase activity in adulthood has never been explained. In addition, it has been suggested that lactase-phlorizin hydrolase is associated with glycosylceramidase activity when the enzyme is prepared by column chromatography, but it is unclear whether this represents copurified activities or two catalytic sites on one peptide. The developmental patterns of lactase-phlorizin hydrolase and other disaccharidases were investigated in homogenates of total rat small intestine; lactase and several glycosylceramidases were measured in immunoprecipitates from these homogenates using a monoclonal antibody. The developmental pattern of total lactase activity showed a steady 2.3-fold increase to adult levels (specific activity decreased eightfold), whereas total phlorizin-hydrolase activity increased 10.7-fold (specific activity decreased threefold). As expected, levels of both total and specific sucrase and maltase activities increased during development. In lactating rats total lactase activity showed a significant increase compared with adult males. The developmental pattern of the enzyme activities for the glycolipid substrates was similar to that found for lactase, and the immunoprecipitated enzyme showed a 40- to 55-fold higher affinity for the glycolipids than for lactose. Galactosyl- and lactosylceramide inhibited lactose hydrolysis by 38%, without a competitive pattern, suggesting two different active sites for lactose and glycolipid hydrolysis, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:New insights into lactase and glycosylceramidase activities of rat lactase-phlorizin hydrolase. 250 86

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

Explants of pig small intestine were maintained at 37 degrees C in organ culture for periods up to 24 h in a system using Trowell T-8 medium supplemented with 10% foetal-calf serum. The mucosal morphology was well preserved during culture, as judged by light and electron microscopy. The explant contents of protein and two brush-border enzymes, microvillus aminopeptidase (EC 3.4.11.2) and dipeptidyl peptidase IV (EC 3.4.14.5), were not significantly modified during culture compared with controls, but a moderate, continuous release of both protein and enzyme activities into the medium was observed. Continuous labelling with [35S]methionine resulted in an even incorporation of radioactivity in the protein components, and the rate of labelling only moderately decreased over the 24 h period. The polypeptide compositions of sucrase (EC 3.2.1.48)--isomaltase (EC 3.2.1.10), maltase--glucoamylase (EC 3.2.1.20) lactase (EC 3.2.1.23)--phlorizin hydrolase (EC 3.2.1.62), microvillus aminopeptidase and aspartate aminopeptidase (EC 3.4.11.7) synthesized during culture were studied, and some were found to be similar to those of the pro-forms of the enzymes isolated from animals that had had their pancreatic duct disconnected 3 days before being killed. These results confirmed earlier findings of the existence of pro-forms of some of the microvillar enzymes and thus indicate a low activity of pancreatic proteinases in the culture system.
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PMID:Biosynthesis of intestinal microvillar proteins. Characterization of intestinal explants in organ culture and evidence for the existence of pro-forms of the microvillar enzymes. 709 36

Conscious unrestrained piglets were fasted overnight and infused intravenously with [2H3]leucine for 6 h. Sucrase isomaltase and lactase phlorizin hydrolase were immunoprecipitated from jejunal mucosal membranes, and the immunoprecipitates were electrophoresed on polyacrylamide gels. Bands corresponding to the pro and mature isoforms of both enzymes were acid hydrolyzed. [2H3]leucine isotopic enrichment was measured by gas chromatography-mass spectrometry using negative chemical ionization. Plasma leucine reached isotopic steady state within 90 min. The isotopic enrichment of mucosal leucine was 73% of that of plasma leucine. The high mannose and complex glycosylated forms of prolactase were in isotopic equilibrium, and their isotopic enrichment was 94% of mucosal leucine. The fractional synthesis rates of total and membrane protein were 0.45 and 0.65 days-1, whereas the processing rates of mature lactase, sucrase, and isomaltase were 0.90, 0.23, and 0.21 days-1, respectively. Approximately 65% of the label in the sucrase isomaltase immunoprecipitate was in the complex glycosylated precursor, whereas 73% of the label in lactase phlorizin hydrolase was in the mature (160 kDa) form. We conclude that the low rate of brush-border sucrase synthesis reflects a slow rate at which the complex glycosylated precursor is processed to the brush-border form.
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PMID:Brush-border disaccharidase synthesis in infant pigs measured in vivo with [2H3]leucine. 781 Jun 60

To assess the role of pancreatic proteases in the proteolytic processing and in the postweaning decline of lactase-phlorizin hydrolase (LPH), we have determined lactase activity and the different LPH forms in postweaned rats in which a jejunal loop was excluded from contact with pancreatic secretions by a jejunal bypass procedure. As a control for the absence of pancreatic proteases, pro-sucrase-isomaltase (proSI), which is known to be split by pancreatic proteases into heterodimeric SI, was used. Nearly all proLPH was processed to mature LPH, indistinguishable from LPH isolated from control animals. SI was found only in the unsplit pro form, whereas it was normally processed to the heterodimeric SI in the control tissues. There were no significant differences in lactase and sucrase activities in operated and in sham-operated control animals. We conclude that pancreatic secretions are not essential for the processing of proLPH to LPH or in the postweaning decline of LPH.
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PMID:Do pancreatic proteases play a role in processing prolactase and/or in the postweaning decline of lactase? 784 Feb 6


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