Synthesis of (2R)-glycerol-o-beta-D-galactopyranoside by beta-galactosidase.
TL;DR: In this paper, the preparation of (2R)-Glycerol-o-D-β-galactopyranoside and radioactively labeled RGG is discussed.
Abstract: Publisher Summary This chapter discusses the preparation of (2R)-Glycerol-o-D-β-galactopyranoside and radioactively labeled RGG. (2R)-Glycerol-o-D-β-galactopyranoside (RGG) with its two glyceryl hydroxyl groups acylated by fatty acids occurs in large amounts in the chloroplasts of plants and algae as one type of galactolipid. After the deacylation of the two fatty acids of the galactolipid, RGG is a carbon source for enteric bacteria, such as Escherichia coli, endowed with lac operon-encoded proteins. By comparing the utilization by E. coli of lactose and RGG, it is proposed that RGG is the natural substrate of the lac operon-encoded metabolic functions of enteric bacteria. The isolation of RGG is accomplished by extracting galactolipids from chloroplasts, deacylating by alkaline hydrolysis, and chromatographic separation of glycerol mono- and digalactosides followed by the crystallization of RGG. The initial crystallization of RGG occur faster if the syrup containing RGG is passed over a BioGel P-2 column after dissolving in 50 ml of water and elution in water.
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TL;DR: A review about the potential of enzymes as catalysts for the synthesis of carbohydrates: advances in the enzyme-catalysed construction of natural and unnatural monosaccharides; methods for enzyme-Catalysed formation of glycosyl bonds by Lenoir and non-Lenoir pathways.
320 citations
TL;DR: The synthetic utility of glycosidases would be considerably improved if methods could be found for maintaining their catalytic activity in non-aqueous media.
Abstract: Glycosidases catalyse the synthesis of anomerically pure alkyl glycosides in one step. In contrast, chemical synthesis of anomerically pure glycosides is circuitous and expensive. Two methodologies are used in enzymatic glycosylation: thermodynamically controlled reversed hydrolysis and kinetically controlled transglycosylation. The advantages and limitations of both approaches are delineated. Glycosidases exhibit broad specificity with regard to the aglycon: in addition to simple alcohols, hydroxy amino acids, nucleosides, ergot alkaloids and cardiac genins are glycosylated. Non-alcohol acceptors such as oximes and thiols also function as substrates whereas pyranoid glycals act as non-natural donors. Glycosidases exhibit absolute selectivity with regard to the stereochemistry at the anomeric centre and show a high degree of chemoselectivity for different hydroxyl groups, e.g., the order of reactivity is primary>secondary alcohols>phenols; tertiary alcohols are unreactive. Chiral primary alcohols are poorly discriminated, but the enantioselectivity towards a hydroxyl group that is directly attached to a (pro)chiral carbon atom is often high. The synthetic utility of glycosidases would be considerably improved if methods could be found for maintaining their catalytic activity in non-aqueous media.
263 citations
TL;DR: The glucose binding site of β-galactosidase played an important role in lac operon evolution and defines an “allolactose synthesis motif” that is co-selected with lac repressors.
40 citations
TL;DR: A comparison has been made between the physiology and amino acid sequence of the lactose carrier of Klebsiella pneumoniae M5a1 and Escherichia coli K-12 and the amino acid sequences of the respective lactose carriers were remarkably similar.
38 citations
TL;DR: Acyl-3-O-β-d -Galactopyranosyl glycerides have been prepared by β-galactosidase catalysed transgalacto-sidation of lactose with 2,3-epoxypropanol with a fatty acid.
38 citations
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302 citations
TL;DR: The Galactose binding protein is the part of the galactose chemoreceptor which recognizes the attractants galactOSE, glucose, and a number of structurally related chemicals.
Abstract: The galactose binding protein is the part of the galactose chemoreceptor which recognizes the attractants galactose, glucose, and a number of structurally related chemicals.
266 citations
TL;DR: It was shown that allolactose could also be formed in significant quantities by the transfer of galactose to the 6 position of free glucose, and also by hydrolysis of preformed trisaccharide, and the mechanism which fits the initial velocity data was proposed.
Abstract: A study was implemented to quantitate the hydrolase and transgalactosylase activities of beta-galactosidase (E. coli) with lactose as the substrate and to investigate various factors which affect these activities. At low lactose concentrations the rate of galactose production was equal to the rate of glucose production. The rate of galactose production relative to glucose, however, dropped dramatically at lactose concentrations higher than 0.05 M and production of trisaccharides and tetrasaccharides began (galactose/glucose ratios of about 2:1 and 3:1, respectively, were found for these two types of oligosaccharides). At least five different trissacharides were formed and their patterns of formation showed that they probably utilized both lactose and allolactose as galactosyl acceptors. Allolactose was produced in amounts proportional to glucose at all lactose concentrations (ratios of allolactose/glucose were about 0.88). Analyses of various data, including a reaction analyzed at very early times, showed that the major means of production of allolactose (and the only means initially) was the direct enzymatic transfer of galactose from the 4 position to the 6 position of the glucose moiety of lactose without prior release of glucose from the enzyme. It was shown, however, that allolactose could also be formed in significant quantities by the transfer of galactose to the 6 position of free glucose, and also by hydrolysis of preformed trisaccharide. A mechanism which fits the initial velocity data was proposed in which the steps involving the formation of an enzyme-gallactose-glucose complex, the formation and breakage of allolactose on the enzyme, and the release of glucose all seem to be of roughly equal magnitude and rate determining. Various factors affected the amounts of transgalactosylase and hydrolase activities occurring. At high pH values (greater than 7.8) the transgalactosylase/hydrolyase activity ratio increased dramatically while it decreased at low pH values (less than 6.0). At mid pH values the ratio was essentially constant. The absence of Mg2+ caused a large decrease in the transgalactosylase/hydrolase activity ratio while the absence of all but traces of Na+ or K+ had no effect. The anomeric configuration of lactose altered the transgalactosylase/hydrolase activity ratios, alpha-Lactose resulted in a decrease of allolactose production (transgalactosylase activity) relative to hydrolase activities (glucose production) while beta-lactose had the opposite effect.
240 citations
TL;DR: In vivo, in vivo, synthetic allolactose is a more effective inducer than IPTG ‡ , probably because it is more efficiently concentrated by the permease.
218 citations
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