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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)

A unique demonstration is presented of the capacity of glycosidases to create anomeric configuration de novo. Purifed Candida tropicalis alpha-glucosidase and sweet almond beta-glucosidase have been found to attack the same substrate, D-glucal, and to convert this unusual glycosyl substrate (which lacks alpha or beta anomeric configuration) to 2-deoxy-alpha-(or beta-) D-glucose, respectively. The stereospecificity of the hydration reaction catalyzed by each enzyme in D2O was revealed by the use of high-resolution (270 MHz) 1H magnetic resonance spectroscopy. The alpha-glucosidase caused a specific axial protonation (deuteration) of D-glucal at C-2, and formation of 2-deoxy-alpha-D-[2(a)-2H]glucose. The beta-glucosidase catalyzed an oppositely directed axial protonation at C-2 and formation of 2-deoxy-beta-D-[2(e)-2H]glucose. These results are not accounted for by the generally accepted mechanisms of carbohydrase action derived from studies with glycosidically linked substrates alone. D-Glucal apparently binds to the enzymes with essentially the same overall orientation as the D-glucosyl moiety of glycosidically linked substrates (with the double bond of D-glucal lying essentially in the plane of the similarly bound D-glucosyl group). Thus, the alpha-glucosidase evidently protonates D-glucal from above the double bond and alpha-D-glucosidic substrates from below the glycosidic oxygen; beta-glucosidase apparently protonates D-glucal from below the double bond and beta-D-glucosides from above the glycosidic oxygen. A detailed mechanism is proposed for the hydration of D-glucal by each enzyme, involving an incipient glycosyl carbonium ion and assuming the presence at the active site of two carboxyl groups arranged to account for catalysis of glycosylations from glycosidically linked substrates. That D-glucal serves as a glycosyl substrate for these enzymes strongly supports the concept that glycosidases and glycosyltransferases are catalysts of glycosylation (i.e., glycosylases), since this concept does not make the usual assumption that carbohydrases are restricted to acting on substrates having a glycosidic bond and either alph- or beta-anomeric configuration.
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PMID:Scope and mechanism of carbohydrase action: stereospecific hydration of D-glucal catalyzed by alpha- and beta-glucosidase. 87 25

Microbioassays using bacteria or enzymes are increasingly applied to measure chemical toxicity in the environment. Attractive features of these assays may include low cost, rapid response to toxicants, high sample throughput, modest laboratory equipment and space requirements, low sample volume, portability, and reproducible responses. Enzymatic tests rely on measurement of either enzyme activity or enzyme biosynthesis. Dehydrogenases are the enzymes most used in toxicity testing. Assay of dehydrogenase activity is conveniently carried out using oxidoreduction dyes such as tetrazolium salts. Other enzyme activity tests utilize ATPases, esterases, phosphatases, urease, luciferase, beta-galactosidase, protease, amylase, or beta-glucosidase. Recently, the inhibition of enzyme (beta-galactosidase, tryptophanase, alpha-glucosidase) biosynthesis has been explored as a basis for toxicity testing. Enzyme biosynthesis was found to be generally more sensitive to organic chemicals than enzyme activity. Bacterial toxicity tests are based on bioluminescence, motility, growth, viability, ATP, oxygen uptake, nitrification, or heat production. An important aspect of bacterial tests is the permeability of cells to environmental toxicants, particularly organic chemicals of hydrophobic nature. Physical, chemical, and genetic alterations of the outer membrane of E. coli have been found to affect test sensitivity to organic toxicants. Several microbioassays are now commercially available. The names of the assays and their basis are: Microtox (bioluminescence), Polytox (respiration), ECHA Biocide Monitor (dehydrogenase activity), Toxi-Chromotest (enzyme biosynthesis), and MetPAD (enzyme activity). An important feature common to these tests is the provision of standardized cultures of bacteria in freeze-dried form. Two of the more recent applications of microbioassays are in sediment toxicity testing and toxicity reduction evaluation. Sediment pore water may be assayed directly or solvents may be used to extract the toxicants. Some of the solvents used for extraction of organic chemicals are themselves toxic to bacteria (e.g., dichloromethane), requiring exchange with a less toxic solvent (e.g., ethanol, methanol, DMSO). A modification of the Microtox test allows direct assay of solid-phase samples such as sediments. The toxicity reduction evaluation (TRE) must be carried out at wastewater treatment plants whose effluents fail toxicity standards. The TREs require numerous and repeated toxicity assays, thus favoring application of microbioassays. Presently, no single microbioassay can detect all categories of environmental toxicants with equal sensitivity. Therefore, a battery of tests approach is recommended. The differential sensitivity of alternative tests may, in fact, be exploited. Further research is needed to construct strains of genetically engineered microorganisms or isolate microorganisms or enzymes that respond to specific classes of toxicants. These can be combined into batteries appropriate for different environments or test objectives.
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PMID:Bacterial and enzymatic bioassays for toxicity testing in the environment. 150 75

Growth failure is a major complication of chronic hypoxemia, as seen in infants and children with cyanotic congenital heart disease. To determine whether chronic hypoxemia during infancy affects the gastrointestinal tract, we examined small intestinal growth and digestive enzyme activities in chronically hypoxemic newborn lambs and in age-matched controls. Chronic hypoxemia was produced by placing an inflatable occluder around the main pulmonary artery and performing a balloon atrial septostomy. Aortic oxygen saturation was reduced to 60-74% for 2 wk, after which the small intestine was removed for analysis. During chronic hypoxemia, somatic growth rate was decreased to 60% of control (hypoxemic, 135 +/- 20 versus control, 216 +/- 26 g/d, p less than 0.02). No differences in caloric intake were found (hypoxemic, 129 +/- 4 versus control, 128 +/- 4 kcal/kg/d). Chronic hypoxemia did not alter small intestinal growth, as measured by jejuno-ileal weight, jejuno-ileal length, mucosal weight, or mucosal protein or DNA contents. However, sp act of lactase, the principal disaccharidase of the infant lamb intestine, were significantly decreased (hypoxemic, 0.08 +/- 0.01 versus control, 0.146 +/- 0.03 units of enzyme activity/mg DNA, p less than 0.05), as were the total small intestinal contents of lactase (hypoxemic, 61.7 +/- 7.0 versus control, 120.6 +/- 21.7 units of enzyme activity, p less than 0.01). There also were decreases in specific and total activities of other digestive enzymes such as maltase, amino-oligopeptidase, and alkaline phosphatase in hypoxemic intestine that did not achieve statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Alterations in postnatal intestinal function during chronic hypoxemia. 156 Oct 8

Muscular glycogenosis is a disease resulting from genetic abnormalities altering an enzyme which is involved in glycogen metabolism. In addition to disorders of glycogenolysis and glycolysis, there are other pathological processes such as acid maltase (alpha-glucosidase) deficiency and diseases associated with abnormal glycogen structure. Glycolysis is the only metabolic pathway that can produce ATP in the absence of oxygen. It is then easy to understand that any disturbance in this energy pathway can result in dysfunction of the muscle machine and in a number of symptoms which are common to these abnormalities. An overall review of the various diseases know to exist on the glycogenolytic and glycolytic pathway will enable the reader to acquire a better knowledge of their particular features.
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PMID:[Muscular glycogenoses]. 189 12

Crystalline, alpha-glucosidase-free sweet potato beta-amylase was found to catalyze hydration of the enolic bond of maltal (alpha-D-glucopyranosyl-(1----4)-2-deoxy-D-glucal) to form 2-deoxymaltose (alpha-D-glucopyranosyl-(1----4)-2-deoxy-D-glucose). The reaction at pH 5.0 showed Vmax 0.082 mumol/min/mg and km 94.5 mM. An exceptionally large solvent deuterium isotope effect, VH/VD = 8, was observed from pH(pD) 4.2 to 5.4; and at pH(pD) 5.0 the effect was found to be directly related to the mole fraction of 2H. The hydration product, isolated from a beta-amylase/maltal digest in acetate-d4/D2O buffer (pD 5.4) was identified through its 1H NMR spectrum as alpha-D-glucopyranosyl-(1----4)-2-deoxy-D-[2(a)-2H]glucose. beta-Amylase in 2H2O thus catalyzes deuteration of the double bond of maltal from a direction opposite that assumed for protonation of the glycosidic oxygen atoms of starch chains and maltosaccharides. This finding confirms the functional flexibility of the enzyme's catalytic groups first demonstrated in studies of the reactions catalyzed with alpha- and beta-maltosyl fluoride (Hehre, E. J., Brewer, C. F., and Genghof, D. S. (1979) J. Biol. Chem. 254, 5942-5950). A possible mechanism of the maltal hydration by beta-amylase involves protonation of substrate from above as the first and rate-limiting step, followed by formation of a transient carbonium ion-enzyme intermediate. Although other possible mechanisms cannot be ruled out, it is clear that this hydration reaction differs from reactions catalyzed with amylaceous substrates and with alpha- and beta-maltosyl fluoride. The ability of beta-amylase to catalyze different types of reactions with different substrates is discussed with respect to observations with other enzymes that, likewise, strongly support the view (Hehre et al.) that the catalytic groups of glycosylases in general may be functionally flexible beyond requirements of the principle of microscopic reversibility.
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PMID:Catalytic flexibility of glycosylases. The hydration of maltal by beta-amylase to form 2-deoxymaltose. 241 22

The dose dependent effect of superoxide dismutase in providing protection against oxygen free radicals mediated tissue damage was investigated. Xanthine-xanthine oxidase system was used to generate oxygen free radicals in vitro and damage renal brush border membrane of mice. At lower concentrations, superoxide dismutase was found to rather aggravate renal brush border membrane damage as shown by significant increase (p less than 0.05) in the malondialdehyde levels and corresponding decrease (p less than .05) in the activities of marker enzymes of renal tissue injury i.e. alkaline phosphatase, gamma-glutamyl transpeptidase and leucine aminopeptidase except maltase whose activity increased correspondingly. At higher doses of superoxide dismutase, significant protection (p less than .05) was observed against tissue damage in a dose dependent manner. On the other hand, catalase and mannitol provided dose dependent protection and their combinations with superoxide dismutase could alleviate the enhanced tissue damage produced by lower doses of superoxide dismutase. The implications of these findings have been discussed.
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PMID:Concentration dependent function of superoxide dismutase in oxygen free radicals mediated tissue injury in renal brush border membrane. 281 3

Reactive oxygen species have been found to be responsible for the tissue injury caused in experimental pyelonephritis in mice. The extent of lipid peroxidation (as assayed by malondialdehyde formation) was found to be increased significantly (p less than .001) in the infected group as compared to the normal mice. Superoxide dismutase and catalase (oxygen free radical scavengers) showed a significant decrease (p less than .001) in the extent of lipid peroxidation even in the presence of infection. Dimethyl sulfoxide, a hydroxyl ion scavenger, was however found to be effective only at 4 and 7 days postinfection (p less than .001). Allopurinol, an inhibitor of xanthine oxidase, did not significantly (p greater than .05) inhibit the formation of lipid peroxides, even upto 7 days postinfection. There was a significant decrease (p less than .05) in the activities of renal brush border membrane enzymes used as markers of renal tissue damage (i.e. alkaline phosphatase, leucine amino-peptidase and gamma-glutamyl transpeptidase) in the infected group as compared to the normal group. In the presence of superoxide dismutase, dimethylsulfoxide and catalase except allopurinol, the activities of all the enzymes but maltase were found to be increased significantly (p less than .05) as compared to the infected group. There was a significant increase (p less than .01) in the bacterial count in the presence of superoxide dismutase and DMSO in infected mice as compared to the infected control mice. However, no significant difference was observed in the catalase and allopurinol treated groups.
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PMID:Effect of various oxygen free radical scavengers in preventing tissue injury caused by Escherichia coli in pyelonephritic mice. 305 56

The effect of the mitogen concanavalin A (Con A) on growth and several physiological aspects of Bacillus cereus ATCC 14579 was investigated. Con A at concentrations ranging from 50 to 750 micrograms/ml stimulated growth (the growth rate increased from 0.52/h to 0.97/h, and final yield increased by 2.3-fold over the control) of the bacterial cells. Con A-treated cells also increased their oxygen uptake (1.6-fold increase when treated with 750 micrograms/ml of Con A). The activities of the membrane-bound dehydrogenase and phosphatase increased by 1.75-fold and 2.1-fold, respectively, when treated with 500 micrograms/ml of Con A. However, only a one-fold increase in alpha-glucosidase activity was observed when cells were treated with the same concentration of Con A. Con A at concentrations of 500 to 1,000 micrograms/ml stimulated the cellular synthesis of cyclic guanosine 3',5'-monophosphate (cGMP) by one-fold. It is proposed that binding of Con A to the cell envelope led to increased synthesis of cGMP which might serve as an intracellular messenger for expression of the mitogenic signal of Con A. Since the use of 50 mg/ml of alpha-methyl-D-mannopyranoside (alpha-MM), a Con A inhibitor, could reverse the stimulatory effect of Con A, it was obvious that the stimulatory action was initiated by the specific binding of Con A molecules to the cell envelope. Furthermore, the stimulatory effect was found to be Con A dosage dependent.
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PMID:Physiological responses of Bacillus species to concanavalin A. 2. Effect on growth, oxygen uptake, enzyme activities and intracellular cyclic guanosine 3',5'-monophosphate level of B. cereus ATCC 14579. 632 27

The suspension of baker's yeast Saccharomyces cerevisiae, race 14, was exposed to a magnetic field, oxygen saturation, and oxygen saturation in the magnetic field. It was found that saturation of the yeast suspension passed at a rate of 1--3 m/min through a magnetic field of 3.10(5)--4.10(5) A/m with molecular oxygen at a pressure of 0.1 MPa to reach a concentration of 16--20 mg/l resulted increases of the yeast rising force, gas formation, 1.5--2.0-fold fermentation rate, 3.7-fold maltase activity, and 3-fold dough viscosity as compared to the control.
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PMID:[Influence of oxygen saturation of Saccharomyces cerevisiae suspension in a magnetic field on yeast activity]. 701 26

Screening in batch cultures identified Debaryomyces yamadae as a yeast that exhibits the Kluyver effect for sucrose: this disaccharide can be respired but, even under oxygen-limited conditions, alcoholic fermentation of sucrose does not occur. Ethanol, glycerol and arabitol were the main fermentation products during oxygen-limited growth on glucose in chemostat cultures. None of these fermentation products were produced in oxygen-limited chemostat cultures grown on sucrose and the fraction of the sucrose that could not be respired remained unused in the culture medium. This absence of alcoholic fermentation was not due to repression of the key fermentative enzymes pyruvate decarboxylase and alcohol dehydrogenase. In contrast to some other yeasts that exhibit a Kluyver effect, D. yamadae did not exhibit a preference for ethanol in batch cultures grown on mixtures of ethanol and sucrose. Sucrose metabolism in D. yamadae involves intracellular hydrolysis by an alpha-glucosidase. Incubation of weakly buffered cell suspensions with sucrose led to a rapid transient alkalinization, indicating the presence of a sucrose-proton symport system. The apparent substrate saturation constant of the sucrose-uptake system was 0.2 mmol l-1. Sucrose-dependent alkalinization rates were much lower in samples from oxygen-limited cultures than in samples from aerobic cultures. Transient responses of D. yamadae to oxygen limitation were investigated by applying a sudden decrease in the oxygen feed to aerobic sugar-limited chemostat cultures. In glucose-grown cultures, this led to alcoholic fermentation and no significant accumulation of sugar occurred after the switch. In sucrose-limited cultures, sugar accumulation occurred instantaneously after the switch, and ethanol formation was virtually absent.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Coordination of sucrose uptake and respiration in the yeast Debaryomyces yamadae. 755 Oct 25


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