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)

The hydrolysis of maltose and isomaltose and of sucrose and isomaltose at two different catalytic sites of sucrase-isomaltase has been demonstrated. Maltose and sucrose are competing for the same catalytic center. This competing can be described by alternative substrate kinetics. Steady-state kinetic parameters Km and k0 (maximal reaction velocity per mol enzyme) for linear alpha-1,4 and alpha-1,6 glucosyloligosaccharides has been determined. Using these parameters subsite affinities for the catalytic sites of sucrase and isomaltase were computed. The different numbers of subsites for sucrase (2 subsites) and isomaltase (4 subsites) indicate, that the binding patterns for maltooligosaccharides and isomaltooligosaccharides are different. That means that for sucrase unproductive enzyme-maltooligosaccharide complexes are definitely less probable than the productive one. As in human small intestinal glucoamylase-maltase in the isomaltase moiety four subsites can be evaluated with affinity values (Ai): A1 = 2.6 (+/- 0.91), A2 = 13.8 (+/- 0.70), A3 = 1.1 (+/- 0.13) and A4 = 1.5 (+/- 0.13) kJ/mol using isomaltooligosaccharides. The two subsites of sucrase are evaluated to be A1 = 4.9 (+/- 0.70) and A2 = 16.7 (+/- 0.51) kJ/mol using maltooligosaccharides. The four subsite model for isomaltase and glucoamylase-maltase is an indication that these two enzymes are mechanistically homologous in binding linear glucosyl-oligosaccharides.
 ...
PMID:Human small intestinal sucrase-isomaltase: different binding patterns for malto- and isomaltooligosaccharides. 762 34

The anaerobic parasitic protist Trichomonas vaginalis was adapted in chemostats to eight different conditions defined by different growth rates and carbon regimens. Glucose or maltose was used as carbon and energy source. Cells cultured under well-defined steady states were tested in short-term experiments. The kinetics of glucose and maltose uptake were determined and their glucokinase and alpha-glucosidase activities were measured. Uptake in 20 min was measured with radiolabelled glucose and maltose, rather than analogues, using the silicone oil centrifugation technique. Hence, the accumulated label represents both transport and metabolic activity. The total uptake of glucose was highest in organisms that had been starved for glucose during growth. The kinetics of glucose uptake can be understood by assuming rate-limitation by transport across the plasma membrane at low external concentrations and by the subsequent metabolism at concentrations exceeding a cross-over value. The specific glucokinase activity correlated in only four out of eight cases with the saturation uptake. The kinetics of maltose uptake indicated rate-limitation at low maltose concentrations by a diffusion-limited step and at higher levels by metabolic steps. The uptake of maltose was primarily affected by the growth rate during culture, the highest growth rates resulting in most uptake. Maltose uptake was determined only partially by the cellular alpha-glucosidase activity. The activities of both transport and metabolic enzymes changed due to the culture conditions suggesting that the control over glucose and maltose metabolism is shared by several steps in the pathway.
 ...
PMID:Adaptation of the carbon metabolism of Trichomonas vaginalis to the nature and availability of the carbon source. 795

Maltose utilization in yeast requires the presence of any one of the five unlinked, homologous MAL loci. Transcription of the two structural genes MALT (permease) and MALS (maltase) is induced by maltose and catabolite-repressed by glucose. MAL6T and MAL6S share a common 5' intergenic sequence; deletion studies within this sequence revealed a bi-directionally functioning upstream activation sequence (UASM) consisting of four 11 bp homologous sites. Activation of these sites by the MALR protein results in the coordinate expression of MAL6T and MAL6S. The basal promoter activates MALS expression to a greater extent than MALT and is located in a region that overlaps UASM. Deletion of several subsites within the UASM has an asymmetric effect on MAL gene expression, having a greater affect on MALT than on MALS. Catabolite repression of MAL6T and MAL6S by glucose is controlled at several levels. Using disruption mutants, the positively acting MAL1R protein was also found to play a role in catabolite repression of MAL6T and MAL6S.
 ...
PMID:Shared control of maltose induction and catabolite repression of the MAL structural genes in Saccharomyces. 802 78

Maltose fermenting strains of Saccharomyces cerevisiae have one or more complex loci called MAL. Each locus comprises at least three genes: MALx1 encodes maltose permease, MALx2 encodes maltase, and MALx3 encodes an activator of MALx1 and MALx2 (x denotes one of five MAL loci, with x = 1, 2, 3, 4, or 6). The MAL43c allele is constitutive and relatively insensitive to glucose repression. To understand better this unique phenotype of MAL43c, we have isolated several MAL63c constitutive mutants from a MAL6 strain. All constitutive mutants remain glucose repressible, and all have multiple amino acid substitutions in the C-terminal region, now making this region of Mal63cp similar to that of Mal43cp. These changes have been generated by gene conversion, which transfers DNA from the telomeres of chromosome II and chromosome III or XVI to chromosome VIII (MAL6). The removal of a Mig1p binding site from the MAL63c promoter leads to a loss of glucose repression, imitating the phenotype of MAL43c. Conversely, addition of a Mig1p binding site to the promoter of MAL43c converts it to glucose sensitivity. Mig1p modulation of Mal63p and Mal43p expression therefore plays a substantial role in glucose repression of the MAL genes.
 ...
PMID:Removal of Mig1p binding site converts a MAL63 constitutive mutant derived by interchromosomal gene conversion to glucose insensitivity. 877 May 84

Maltose metabolism was investigated in the hyperthermophilic archaeon Thermococcus litoralis. Maltose was degraded by the concerted action of 4-alpha-glucanotransferase and maltodextrin phosphorylase (MalP). The first enzyme produced glucose and a series of maltodextrins that could be acted upon by MalP when the chain length of glucose residues was equal or higher than four, to produce glucose-1-phosphate. Phosphoglucomutase activity was also detected in T. litoralis cell extracts. Glucose derived from the action of 4-alpha-glucanotransferase was subsequently metabolized via an Embden-Meyerhof pathway. The closely related organism Pyrococcus furiosus used a different metabolic strategy in which maltose was cleaved primarily by the action of an alpha-glucosidase, a p-nitrophenyl-alpha-D-glucopyranoside (PNPG)-hydrolyzing enzyme, producing glucose from maltose. A PNPG-hydrolyzing activity was also detected in T. litoralis, but maltose was not a substrate for this enzyme. The two key enzymes in the pathway for maltose catabolism in T. litoralis were purified to homogeneity and characterized; they were constitutively synthesized, although phosphorylase expression was twofold induced by maltodextrins or maltose. The gene encoding MalP was obtained by complementation in Escherichia coli and sequenced (calculated molecular mass, 96,622 Da). The enzyme purified from the organism had a specific activity for maltoheptaose, at the temperature for maximal activity (98 degrees C), of 66 U/mg. A Km of 0.46 mM was determined with heptaose as the substrate at 60 degrees C. The deduced amino acid sequence had a high degree of identity with that of the putative enzyme from the hyperthermophilic archaeon Pyrococcus horikoshii OT3 (66%) and with sequences of the enzymes from the hyperthermophilic bacterium Thermotoga maritima (60%) and Mycobacterium tuberculosis (31%) but not with that of the enzyme from E. coli (13%). The consensus binding site for pyridoxal 5'-phosphate is conserved in the T. litoralis enzyme.
 ...
PMID:Maltose metabolism in the hyperthermophilic archaeon Thermococcus litoralis: purification and characterization of key enzymes. 1034 46

To utilise maltose as a carbon source Saccharomyces cerevisiae needs one or more functional MAL loci that contain the MALx1 gene encoding maltose permease, MALx2 encoding maltase, and MALx3 encoding a transcriptional activator. Maltose causes a rapid MALx3-dependent induction of MAL gene transcription, and glucose represses this activation via Mig1p. A MALx3 gene conveying high MAL gene expression in the absence of maltose in a malx3 laboratory mutant strain has been isolated from baker's yeast. The construction of hybrid genes between the isolated gene and a highly regulated MALx3 gene showed that constitutivity was the result of multiple amino-acid alterations throughout the structural gene. The combined effect of these amino-acid alterations was shown to be stronger than the sum of their individual effects on constitutivity. Analysis in glucose-repressed conditions confirmed that increased MALx3 transcript levels increased the glucose insensitivity of MAL gene expression but did not affect constitutivity. Analysis of four mutations between aa 343 and 375, lying within a proposed negative regulatory domain, showed that the single mutation of Leu343Phe increased the glucose insensitivity of MAL gene expression by 30-fold. These results demonstrate that not only Mig1p modulation of MALx3 expression, but also the MALx3 protein structure, is involved in the glucose-insensitive expression of the MAL genes.
 ...
PMID:Leu343Phe substitution in the Malx3 protein of Saccharomyces cerevisiae increases the constitutivity and glucose insensitivity of MAL gene expression. 1036 55

A novel alpha-glucosidase with an apparent subunit mass of 59 +/- 0. 5 kDa was purified from protein extracts of Rhizobium sp. strain USDA 4280, a nodulating strain of black locust (Robinia pseudoacacia L), and characterized. After purification to homogeneity (475-fold; yield, 18%) by ammonium sulfate precipitation, cation-exchange chromatography, hydrophobic chromatography, dye chromatography, and gel filtration, this enzyme had a pI of 4.75 +/- 0.05. The enzyme activity was optimal at pH 6.0 to 6.5 and 35 degrees C. The activity increased in the presence of NH4+ and K+ ions but was inhibited by Cu2+, Ag+, Hg+, and Fe2+ ions and by various phenyl, phenol, and flavonoid derivatives. Native enzyme activity was revealed by native gel electrophoresis and isoelectrofocusing-polyacrylamide gel electrophoresis with fluorescence detection in which 4-methylumbelliferyl alpha-glucoside was the fluorogenic substrate. The enzyme was more active with alpha-glucosides substituted with aromatic aglycones than with oligosaccharides. This alpha-glucosidase exhibited Michaelis-Menten kinetics with 4-methylumbelliferyl alpha-D-glucopyranoside (Km, 0.141 microM; Vmax, 6.79 micromol min-1 mg-1) and with p-nitrophenyl alpha-D-glucopyranoside (Km, 0.037 microM; Vmax, 2.92 micromol min-1 mg-1). Maltose, trehalose, and sucrose were also hydrolyzed by this enzyme.
 ...
PMID:Purification and characterization of an alpha-glucosidase from Rhizobium sp. (Robinia pseudoacacia L.) strain USDA 4280. 1038 82

Some industrial strains of Saccharomyces cerevisiae are unable to maintain high rates of fermentation during transition from catabolism of hexoses to maltose. This phenomenon, termed 'maltose lag', presents problems for the baking, brewing and distilling industries, which rely on yeast catabolism of mixtures of hexoses and maltose. Maltose utilisation requires the presence of maltose permease and alpha-glucosidase (maltase), encoded by MAL genes. Synthesis of these is induced by maltose and repressed by glucose. One strain of baker's yeast used in this work exhibited a marked maltose lag, whereas a second strain exhibited a shorter lag during conversion from hexose to maltose metabolism. The extent of the lag was linked to the levels of maltose permease and maltase in cells at the time of inoculation into mixed sugar medium. This view is supported by results showing that pulsing yeast with maltose to induce expression of MAL genes prior to inoculation into mixed sugar medium, enhanced sugar fermentation. Maltose pulsing of yeasts could therefore be useful for enhancing some fermentations relevant to baking and other yeast industries.
 ...
PMID:Enhancement of maltose utilisation by Saccharomyces cerevisiae in medium containing fermentable hexoses. 1045 90

Maltose transport and maltase activities were inactivated during sporulation of a MAL constitutive yeast strain harboring different MAL loci. Both activities were reduced to almost zero after 5 h of incubation in sporulation medium. The inactivation of maltase and maltose permease seems to be related to optimal sporulation conditions such as a suitable supply of oxygen and cell concentration in the sporulating cultures, and occurs in the fully derepressed conditions of incubation in the sporulation acetate medium. The inactivation of maltase and maltose permease under sporulation conditions in MAL constitutive strains suggests an alternative mechanism for the regulation of the MAL gene expression during the sporulation process.
 ...
PMID:Inactivation of maltose permease and maltase in sporulating Saccharomyces cerevisiae. 1077 76

The objectives of this study were to examine the effects of growth substrate and extracellular pH on phosphoenolpyruvate-dependent glucose phosphorylation as well as to examine how maltose is phosphorylated by the ruminal bacterium Megasphaera elsdenii B159. Phosphoenolpyruvate-dependent glucose phosphorylation by toluene-treated cells was constitutive, and glucose phosphorylation was reduced by 69% at pH 5.0. When toluene-treated cells were incubated in histidine buffer, little maltose phosphorylation occurred in the absence of inorganic phosphate. However, the addition of increasing concentrations of either potassium or sodium phosphate increased maltose phosphorylation. Maximal phosphorylation activity was observed at between 25 and 50 mM of either inorganic phosphate source. Compared with the control incubations, maltose phosphorylation was increased over threefold with 25 mM of either potassium or sodium phosphate. Phosphoglucomutase activity was detected in cell extracts of M. elsdenii B159, and this enzyme had a K(m) of 3.2 mM for glucose-1-P and a V(max) of 1836 nmol of NADP(+) reduced/mg of protein per min. Maltose was also hydrolyzed by an inducible maltase (K(m), 1.19 mM). To our knowledge, this is the first report of a maltose phosphorylase and a maltase in M. elsdenii.
 ...
PMID:Factors affecting glucose and maltose phosphorylation by the ruminal bacterium Megasphaera elsdenii. 1082 81


<< Previous 1 2 3 4 5 Next >>