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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)

Production of extracellular alpha-glucosidase was studied with strain KP 1006 of a new species of thermophilic Bacillus, which was isolated from soil samples by enrichment at 65 C. alpha-Glucosidase production was maximum at 60 C and at an initial pH of 6.5. The final enzyme yield was increased by starch, maltose, glycerol, peptone, and yeast extract but reduced by acetate and gluconate, alpha-Glucosidase was formed in the cytoplasm and accumulated as a large pool during the logarithmic growth phase. At a midpoint of this period, the enzyme appeared in the culture broth, and its level increased until the end of the stationary phase.
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PMID:Production of extracellular alpha-glucosidase by a thermophilic Bacillus species. 0 93

A recessive mutant cat1-1, wild type CAT1, was isolated in Saccharomyces cerevisiae. It did not grow on glycerol nor ferment maltose even with fully constitutive, glucose resistant maltase synthesis. It prevented derepression of isocitrate lyase, fructose-1,6-diphosphatase and maltase in a constitutive but glucose sensitive maltase mutant. Derepression of malate dehydrogenase was retarded and slowed down. Sucrose fermentation and invertase synthesis was not affected. Respiration was normal. From this mutant, two reverse mutants were isolated. One was recessive, acted as a suppressor of cat1-1 and was called cat2-1, wild type CAT2; the other was dominant and allelic to CAT1 and designated CAT1-2d and cat2-1 caused an earlier derepression of enzymes studied but did not affect the repressed nor the fully derepressed enzyme levels. CAT1-2d and cat2-1 did not show any additive effects. It is proposed that carbon catabolite repression acts in two ways. The direct way represses synthesis of sensitive enzymes, during growth on repressing carbon sources whereas the other way regulates the derepression process. After alleviation of carbon catabolite repression, gene CAT1 becomes active and prevents the activity of CAT2 which functions as a repressor of sensitive enzyme synthesis. The CAT2 gene product has to be eliminated before derepression can actually occur. The time required for this causes a delay in derepression after the depletion of a repressible carbon source. cat1-1 cannot block CAT2 activity and therefore, derepression is blocked. cat2-1 is inactive and derepression can start after carbon catabolite repression has ceased. CAT1-2d permanently active as a repressor of CAT2 and eliminates the delay in derepression.
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PMID:Genetics of carbon catabolite repression in Saccharomycess cerevisiae: genes involved in the derepression process. 19 40

Mutants altered in carbon catabolite regulation have been isolated by selecting for mutants of the areA217 strain capable of using acetamide as the sole nitrogen source in the presence of sucrose. In addition to creA mutants described previously be Arst and Cove, strains with mutations in two new genes, creB and cre C, have been found. The creB and creC mutants grow poorly on some sole carbon sources and have low levels of some enzymes of carbon catabolism e.g. beta-galactosidase and D-quinate dehydrogenase. The creB and creC mutants are hypersensitive to fluoroacetate, fluoroacetamide and allyl alcohol in the presence of glucose or sucrose but not glycerol; and the enzymes, acetamidase and alcohol dehydrogenase, are less sensitive to carbon catabolite repression than the wild-type strain. Extracellular protease and alpha-glucosidase enzyme activities are elevated in creB and creC mutants, while L-proline and L-glutamate uptake capacities are lower in both the presence and absence of glucose. Interactions between creA, B and C mutations have been investigated in double mutants, and the dominance properties of creB and creC mutants determined. The results indicate that the creB and creC genes may have a regulatory role in the control of carbon catabolism.
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PMID:Pleiotropic mutants of Aspergillus nidulans altered in carbon metabolism. 32 Apr 55

Studies of substrate and cosubstrate specificities of mould alpha-glucosidases suggest that the binding site of the active center of mould alpha-glucosidase consits of two subsites--glucone and aglucone ones. The glucone site is capable to bind glucose and mannose, whereas the aglucone one- some compounds whose affinity for the enzyme may be expressed as follows: glucose greater than galactose greater than paranitrophenol greater than or equal to glycerol greater than ethanol approximately equal to methanol. Upon interaction of enzyme with alpha-D-glucoside the formation of a productive enzyme-substrate complex occurs when the glucosyl residue located at the non-reducible end of the substrate molecule occupies the glucone subsite and aglucone of the substrate occupies the aglucone subsite of the enzyme. After removal of the first product from the aglucone subsite the substrate is bound at this subsite. It is assumed that under cosubstrate excess it is capable to bind at the aglucone subsite prior to the removal of the first product and the formation of the substituted form enzyme--glycosyl. Under these conditions the cosubstrate removes the substrate from the aglucone subsite resulting in a formation of a non-productive tertiary complex enzyme--substrate--cosubstrate. The anomeric configuration of glucose produced under the action of alpha-glucosidase on maltose and starch was determined using a kinetic method.
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PMID:[Specificity of fungal alpha-glucosidases]. 91 42

The purification of guinea-pig intestinal brush borders by a rapid sucrose-gradient-centrifugation step is reported. A 29-fold increase in the maltase/DNA quotient indicates considerable purification of the brush borders from nuclei. The biological activity of the brush borders was well preserved, as demonstrated by a high recovery of human gastric-juice-mediated uptake of 57Co-labelled vitamin B-12; homogeneity and purity were confirmed by scanning electron microscopy. Both the morphological appearance and biological activity were unchanged after prolonged storage in glycerol.
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PMID:Purification and characterization of guinea-pig intestinal brush borders. 121 22

The MAL1 locus of Saccharomyces cerevisiae comprises three genes necessary for maltose utilization. They include regulatory, maltose transport and maltase genes designated MAL1R, MAL1T and MAL1S respectively. Using a MAL1 strain transformed with an episomal, multicopy plasmid carrying the MAL2 locus, five recessive and one dominant mutant unable to grow on maltose, but still retaining a functional MAL1 locus were isolated. All the mutants could use glycerol, ethanol, raffinose and sucrose as a sole carbon source; expression of the maltase and maltose permease genes was severely and coordinately reduced. Only the dominant mutant failed to accumulate the MAL1R mRNA.
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PMID:Isolation and characterization of maltose non utilizing (mnu) mutants mapping outside the MAL1 locus in Saccharomyces cerevisiae. 203 32

In hex2 mutants of Saccharomyces cerevisiae, which are defective in glucose repression of several enzymes, growth is inhibited if maltose is present in the medium. After adding [14C]maltose to cultures growing with ethanol, maltose metabolism was followed in both hex2 mutant and wild-type cells. The amount of radioactivity incorporated was much higher in hex2 than in wild-type cells. Most of the radioactivity in hex2 cells was located in the low molecular mass fraction. Pulse-chase experiments showed that 2 h after addition of maltose, hex2 cells hydrolysed maltose to glucose, which was partially excreted into the medium. 31P-NMR studies gave evidence that turnover of sugar phosphates was completely abolished in hex2 cells after 2 h incubation with maltose. 13C-NMR spectra confirmed these results: unlike those for the wild-type, no resonances corresponding to fermentation products (ethanol, glycerol) were found for hex2 cells, whereas there were resonances corresponding to glucose. Although maltose is taken up by proton symport, the internal pH in the hex2 mutant did not change markedly during the 5 h after adding maltose. The intracellular accumulation of glucose seems to explain the inhibition of growth by maltose, probably by means of osmotic damage and/or unspecific O-glycosylation of proteins. Neither maltose permease nor maltase was over-expressed, and so these enzymes were not the cause of glucose accumulation. Hence, the coordination of maltose uptake, hydrolysis to glucose and glycolysis of glucose is not regulated simply by the specific activity of the catabolic enzymes involved.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Misregulation of maltose uptake in a glucose repression defective mutant of Saccharomyces cerevisiae leads to glucose poisoning. 219 4

When the purified plant glucosidase II was incubated with [3H]Glc2Man9GlcNAc in the presence of glycerol and the products were analyzed by gel filtration, a large peak of radioactivity emerged just before the glucose standard. The formation of this peak was dependent on both the presence of Glc2Man9GlcNAc and the presence of glycerol, and the amount of this product increased with time of incubation and amount of glucosidase II in the incubation. When the incubation was performed with [3H]Glc2Man9GlcNAc plus [14C]glycerol, the product contained both 14C and 3H. Strong acid hydrolysis of the purified product gave rise to [14C]glycerol and [3H]glucose. Various other chemical treatments and chromatographic techniques showed that the product was glucosyl----glycerol. Since the glucose was released by alpha-glucosidase, the product must be glucosyl-alpha-glycerol. This study demonstrates that the processing glucosidase II catalyzes a trans-glycosylation reaction in the presence of acceptors like glycerol. Since this transglycosylation reaction may give rise to unexpected products, investigators should be aware of its possible occurrence.
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PMID:Plant glucosidase II catalyzes a transglucosylation reaction in addition to the hydrolytic reaction. 266 51

The effect of the glucose analogue 5-thio-D-glucose (5TG) on the yeast Saccharomyces cerevisiae was studied. Derepression of mitochondrial respiratory chain cytochromes, alcohol dehydrogenase (isoenzyme II), NADH dehydrogenase and maltase was inhibited by 0.5-2 mM-5TG. Growth rate was only slightly affected. Ethanol was efficiently produced with 2 mM-5TG in medium initially containing 0.25% glucose. Mutants resistant to the growth inhibitory effects of 5TG on glycerol medium showed resistance to the catabolite repressing effects of glucose. Other mutants, known to be catabolite repression resistant, showed resistance to 5TG. The analogue seems to inhibit derepression of glucose repressible enzymes with greater potency than glucose itself.
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PMID:Catabolite repressive effects of 5-thio-D-glucose on Saccharomyces cerevisiae. 330 35

The formation of the oligosaccharide-lipid intermediates of the dolichol pathway by the bovine retina was investigated. Intact retinas were incubated in vitro for various periods of time in the presence of a variety of radioactive sugars (2-[3H]mannose, 6-[3H]glucose, 1-[3H]galactose, 1-[14C]glucosamine) using incubation conditions which have been shown previously to support the glycosylation of rhodopsin. The oligosaccharide-lipids were isolated and partially purified by DEAE cellulose chromatography. After mild acid hydrolysis and reduction, the oligosaccharides were analysed by HPLC. Further identification was obtained by chemical means and after digestion of the oligosaccharides with alpha-mannosidase and endohexosaminidase H. The full array of oligosaccharide-lipids which have been observed in other tissues were detected in the bovine retina, although some striking differences were seen in their relative distribution. Although short-term incubations (up to 15 min) indicated that the major species was the fully glucosylated oligosaccharide-lipid (Glc3Man9GlcNAc2), with longer incubation times the non-glucose-containing intermediate, Man9GlcNAc2, became the predominant species. Since glycerol was the carbon source for these incubations, the possibility was investigated that glucose starvation may have been the basis for this phenomenon, as has been reported in other tissues. It was established that this was not the case. Experiments carried out in the presence of castanospermine and bromoconduritol indicated that alpha-glucosidase activity in the retina may have resulted in the accumulation of the unglucosylated oligosaccharide-lipids. The formation of oligosaccharide-lipid intermediates by cells of the retinal pigment epithelium from the embryonic chick, maintained in cell culture, was also examined. In contrast to the bovine retina, the major species present were the glucose-containing intermediates, similar to other tissues.
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PMID:The dolichol pathway in the retina: oligosaccharide-lipid biosynthesis. 338 23


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