Melibiose

About: Melibiose is a research topic. Over the lifetime, 1002 publications have been published within this topic receiving 27300 citations. The topic is also known as: Melibiose.

Hydrolysis of raffinose in a hollow‐fiber reactor using an unrefined mixture of α‐galactosidase and invertase

Abstract: Summary Raffinose was converted enzymatically in a hollow-fiber reactor to melibiose, sucrose, galactose, glucose, and fructose. The enzymes were a crude extract of ex­ galactosidase and invertase produced by Aspergillus awamori NRRL 4869 on a solid substrate, wheat bran. With a concentration of raffinose, Co, entering the reactor at a flow rate Q, and with C being the concentration of raffinose exiting the reactor, the conversion (C/ Co), was studied as a function of Q at two levels of Co' The data could be fairly well fitted using the analysis of Waterland et al. even though a mixed crude enzyme system was being investigated. It was found empirically that In (C/ Co) was linear in Q-l, with the absolute value of the slope decreasing with increasing Co. The linearity of such plots were predicted by Lewis and Middleman from Waterland et al. for a single enzyme system obeying first-order kinetics, the slope being independent of Co. Although the assumptions involved in this approximate analytical solution are riot valid, the observed linearity of the In(C/Co) vs. Q-l plots is excellent and should prove useful in reactor design considerations.

Induction and genetics of two α-galactosidase activities in Saccharomyces cerevisiae

Abstract: The induction of α-galactosidase of Saccharomyces cerevisiae was investigated. We have demonstrated the existence of inducible internal and external α-galactosidase activities and have studied the relationship between the two α-galactosidases by examining a mutant strain which lacks both the internal and external activities. The mutant possesses a mutation in a single locus (mel 1-1) which does not affect the synthesis of the other galactose pathway enzymes or the ability of the yeast to grow on media containing only galactose as the carbon source. Genetic studies of the mutant indicate that mel 1-1 is recessive and allelic to the wild type allele for melibiose fermentation Mel 1.

Quantitative Model for Gal4p-Mediated Expression of the Galactose/Melibiose Regulon in Saccharomyces cerevisiae

Abstract: A mathematical model based on equilibrium binding between Gal4p and its specific DNA binding site has been developed. A model for GAL gene expression solely due to cooperativity, as a function of Gal4p concentration, has been developed for a gal80 mutant. The above model was extended to include other known regulatory molecules, namely Gal80p and Gal3p. Parameters determined from the above simulation were then used to represent a physiological status of gene expression in response to glucose (in terms of Gal4p concentration) and galactose in a wild-type strain. We demonstrate that in a wild-type strain glucose repression is more stringent due to cooperativity and autogenous regulation, while the induction response to galactose is only through autogenous regulation. The biological significance of autogenous regulation in Saccharomyces cerevisiae is discussed vis-a-vis the lactose operon of Escherichia coli.

D-Glucose 1-phosphate formation by cyanogen-induced phosphorylation of D-glucose. Synthesis, mechanism, and application to other reducing sugars

Abstract: D-Glucose in dilute aqueous solution (pH 6·7–8·8) in the presence of orthophosphate and cyanogen is phosphorylated to produce α-D-glucopyranose 1-phosphate (yield 8–20%), β-D-glucopyranose 1-phosphate (2–5%), and a phosphorylated disaccharide (3–34%). The products were identified by paper chromatography and electrophoresis and by hydrolytic studies. The first-order rate constants for hydrolysis of α- and β-glucopyranose 1-phosphate in 1·16M-perchloric acid at 25° are 4·14 × 10–5 s–1, respectively. α-D-Glucose 1-phosphate (Cori ester) was further identified by a highly specific enzymic assay.The cyanogen-induced phosphorylation is a general reaction for reducing sugars; non-reducing sugars are inert. Thus, phosphorylation is also successful with the monosaccharides D-arabinose, D-ribose, D-xylose, D-galactose, D-mannose, D-fructose, D-glucosamine, N-aceyl-D-glucosamine, and with the disaccharides maltose, melibiose, cellobiose, and lactose, but fails with glycerol, sucrose, and trehalose.In the case of D-arabinose, the products are D-arabinopyranose 1-phosphate and D-arabinofuranose 1-phosphate, obtained in 3–5% and 0·5–1·5% yield, respectively.Evidence for the mechanism of cyanogen-induced phosphorylation was obtained by studying the hydrolysis of cyanogen and orthophosphate in H218O. The observed rapid uptake of 18O into the orthophosphate, without isotopic dilution of the water, indicates initial formation of a cyanogen–phosphate adduct [CN–CN + HPO42–→ NC–C(NH)–O·PO32–] which then undergoes hydrolysis to produce 18O-labelled orthophosphate [NC–C-(NH)–O–PO32–+ H218O → NC·CO·NH2+18O·PO32–]. With an excess of cyanogen, the orthophosphate undergoes further cycles of 18O uptake from the water. In the presence of reducing sugars, the intermediate cyanogen–phosphate adduct acts as a phosphorylating agent, attacking the glycosidic hydroxy-groups to produce glycosyl phosphates. Cyanogen-promoted phosphorylation is suggested as a model for the prebiotic synthesis of sugar phosphates.

Uptake of disaccharides by the aerobic yeast Rhodotorula glutinis. Hydrolysis of beta-fructosides and trehalose.

Abstract: Sucrose (and raffinose), trehalose, maltose, cellobiose, and lactose were examined for their transport into Rhodotorula glutinis. Melibiose and lactose were found not to be transported at all. Sucrose, raffinose and trehalose are split by periplasmic hydrolases prior to the penetration of their monosaccharide components into cells, the hydrolysis being the rate-limiting factor for the uptake process. Maltose and cellobiose appear to use specific uptake systems. Experiments with protoplasts of Rhodotorula glutinis support the conclusions that sucrose and trehalose are not consumed in the absence of exoenzymes.