Showing papers on "Melibiose published in 1988"

Construction of a Stable α-Galactosidase-Producing Baker's Yeast Strain

Abstract: Molasses is widely used as a substrate for commercial yeast production. The complete hydrolysis of raffinose, which is present in beet molasses, by Saccharomyces strains requires the secretion of α-galactosidase, in addition to the secretion of invertase. Raffinose is not completely utilized by commercially available yeast strains used for baking, which are Mel−. In this study we integrated the yeast MEL1 gene, which codes for α-galactosidase, into a commercial mel0 baker's yeast strain. The Mel+ phenotype of the new strain was stable. The MEL1 gene was expressed when the new Mel+ baker's yeast was grown in molasses medium under conditions similar to those used for baker's yeast production at commercial factories. The α-galactosidase produced by this novel baker's yeast strain hydrolyzed all the melibiose that normally accumulates in the growth medium. As a consequence, additional carbohydrate was available to the yeasts for growth. The new strain also produced considerably more α-galactosidase than did a wild-type Mel+ strain and may prove useful for commercial production of α-galactosidase.

A cell-associated oligo-1,6-alpha-glucosidase from an extremely thermophilic anaerobic bacterium, Thermoanaerobium Tok6-B1.

Abstract: Cell-associated oligo-1,6-alpha-glucosidase (EC 3.2.1.10) was isolated from Thermoanaerobium Tok6-B1 grown on starch-containing medium. Activity was purified 11.4-fold by salt precipitation, gel filtration, hydroxyapatite and anion-exchange chromatography. Molecular mass was determined as 30,000 by SDS/polyacrylamide-gel electrophoresis and 33,000 by analytical gel filtration. The probable order of specificity was p-nitrophenyl-alpha D-glucose greater than-isomaltose greater than-isomaltotriose greater than-panose greater than-nigerose and no activity was shown against malto-oligosaccharides, melezitose, melibiose, raffinose, cellobiose, sophorose, gentiobiose, lactose, pullulan, dextran or amylose. The optima for activity and stability were between pH 5.6 and 7.0 and the half-life at pH 6.5 was 1000 min at 70 degrees C and 20 min at 76 degrees C. Activity was stabilized by substrate, Mg2+, Mn2+ and Ca2+, but was destabilized by Zn2+ and EDTA. N-Ethylmaleimide, glucose and 1-O-methyl-alpha D-glucose were inhibitory but 1-O-methyl-beta D-glucose stimulated activity. The activation energy (Ea) was 109 kJ/mol.

Gas Production From Melibiose, Raffinose and White Bean Extracts by Bacteria of Human Fecal Origin

Abstract: Four organisms Peptostreptococcus productus, P. anaerobius, Bacteriodes fragilis ss. distasonis, and Clostridium perfringens all isolated from human feces, were examined for their ability to grow and produce gas from α-galactosides and fractions of white beans (Phaseolus vulgaris var. Seafarer). C. perfringens produced the most gas from substrates, with raffinose and a low molecular weight soluble enzymic digested bean extract promoting the most gas. Insoluble undigestible carbohydrates of bean origin produced lower, but significant, amounts of gas. Melibiose did not promote gas formation, suggesting that the fructose moiety present in raffinose was responsible for gas production.

Feeding by mucin and intestinal growth of some enteric bacterial pathogens.

Abstract: Enteroinvasive Escherichia coli, Salmonella typhi-murium, Shigella sonnei, Shigella flexneri, as well as E. coli K-12 show dose dependent growth in minimal medium completed with purified hog gastric "Granular Mucin". This ability is based on alpha-galactosidase production: defective, melibiose (and galactose) non-fermenting K-12 mutant were unable to utilize mucin. The viability of the parent K-12 strain in the cecal content of mice is significantly higher than that of its Mel- mutant phenotype. In mixed infections of mice the parent strain was the only one to be able to establish a monoflora against its Mel- or Gal- mutants. Among other mechanisms, the growing ability in the intestinal mucous layer may be an additional virulence factor when the enteric pathogens are exposed to a competitive antagonism of the normal flora.

Hemagglutinating activity of the heat-labile enterotoxin isolated from porcine enterotoxigenic Escherichia coli

Abstract: The hemagglutinating activity of the heat-labile enterotoxin (LTp) isolated from porcine enterotoxigenic Escherichia coli was studied by hemagglutination inhibition. The hemagglutinating activity of LTp was enhanced 64–512-fold with pronase- and neuraminidase-treated human erythrocytes although both intact human and sheep erythrocytes were not agglutinated by LTp at the highest concentration used. No enhancement was found in hemagglutination of neuraminidase-treated sheep erythrocytes by LTp. Hemagglutination of pronase-treated human type A erythrocytes induced by LTp was inhibited by melibiose and galactose among mono-, di-, and polysaccharides used as inhibitors. Galactose was a slightly better inhibitor than melibiose. These findings suggest that LTp is a bacterial lectin specific for galactose.

Construction of a vector for the study of regulatory mechanism of gene expression and its utilization in the melibiose operon of Escherichia coli.

Abstract: We constructed a vector to evaluate terminator or attenuator of transcription quantitatively. This vector is a plasmid possessing lac promoter-polylinker-CAT(chloramphenicol acetyltransferase) gene. DNA fragment of interest can be inserted into the polylinker site, and the effect of the DNA fragment on the expression of the downstream gene is evaluated from the CAT activity. We analyzed gene expression of the melibiose operon of Escherichia coli using this plasmid, and found that a DNA fragment containing a large stem-loop structure with boxA sequence in it, which was present between melA and melB, caused strong reduction of gene expression. This DNA portion seems to be responsible for reduced expression of melB, the second gene of the melibiose operon.

Studies on the chemical components of wild Korean lettuce (Youngia sonchifolia Max.).

Abstract: For the effective utilization of Wild Korean lettuce(Youngia sonchifolia Max.), the chemical characteristics, contents of free sugar, amino acid composition, fatty acid composition and minerals were analysed. Free sugars determined from the roots were rhamnose, fructose, glucose, sucrose maltose, melibiose and raffinose, whereas raffinose was not detected from the leaves. Of amino acid composition in the roots glutamic acid content was largest followed by histidine aspartic acid, leucine and proline. As for leaves glutamic acid was highest fellowed by aspartic acid, leucine and histidine. Mtehionine and cystine were found in low content in both roots and leaves. Major fatty acid composition in total lipid(free and bound) were linoleic, linolenic and palmitic acid in both and leaves. P, K and Ca were rich minerals contained in the roots and leaves of Wild Youngia sonchifolia Max.

A new member of the family Enterobacteriaceae--Pragia fontium.

Abstract: Twenty isolates of the new genus and species Pragia fontium producing H2S were biochemically characterized: they gave positive gluconate oxidation, utilized Simmons citrate and 14 of them hydrolysed esculin. One of them did not produce hydrogen sulfide. Their biochemical activity was low: they did not ferment lactose, adonitol, arabinose, cellobiose, dextrin, dulcitol, erythritol, inulin, maltose, mannitol, mannose, melezitose, melibiose, raffinose, rhamnose, sorbitol, sorbose, starch, sucrose or trehalose. The habitat of Pragia fontium is drinking water, with an exception: the last strain was found in a stool specimen of a healthy woman. The type culture is the first isolate No. 20125-HG 16. It is deposited in Prague (CNCTC) under the designation Eb 11/82.