Galactose uridine phosphate

Fermentation procedures useful for the production of uridine 5 -(a-D-galactopyranosyl pyrophosphate) involve the cultivation of bacterial mutant-strains that are deficient in the 4"-epimerase for 30 (see Section V,l,b, p. 369) in D-galactose-containing media,245-247 or by incubating Torulopsis Candida cells with uridine 5 -phosphate, D-galactose, potassium phosphate, and magnesium sulfate.248... 

The galactose 1-phosphate is then converted to its epimer at C-4, glucose 1-phosphate, by a set of reactions in which uridine diphosphate (UDP) functions as a coenzyme-like carrier of hexose groups (Fig. 14-11). The epimerization involves first the oxidation of the C-4 —OH group to a ketone, then reduction of the ketone to an —OH, with inversion of the configuration at C-4. NAD is the cofactor for both the oxidation and the reduction. 

Galactose 1-phosphate then acquires a uridyl group from uridine diphosphate glucose (UDP-glucose), an intermediate in the synthesis of glycosidic linkages (Section 21.4.2). 

Galactose 1-thiophosphate and UDP-glucose Uridine-5 -0-(2- thiodiphosphogalactose) (UDP(JSS)-Galactose (50%) Galactose-1- Phosphate Uridyl Transferase (E.C. 2.7.7.12) [97]... 

Abbreviations used Gal-l-P, galactose-l-phosphate UDPG, uridine diphosphate glucose G-l-P, glucose-l-phosphate G-6-P, glucose-6-phosphate F-6-P, fructose-6-phosphate F-l,6-P, fructose-1,6-diphosphate G-3-P, glyceraldehyde-3-phosphate DHAP, dihydroxyacetone phosphate F-l-P, fructose-1-phosphate PG, 6-phospho-gluconic acid R-5-P, ribulose-5-phosphate S-7-P, sedoheptulose-7-phosphate. 

Scheme 22 The whole biosynthetic pathway of sugar nucleotides. ATP, adenosine triphosphate Gal-1 -P, galactose-1-phosphate UTP, uridine triphosphate UDP, uridine diphosphate NAD, nicotinamide adenine dinucleotide Fru, fructose AcCoA, acetyl coenzyme-A PEP, phosphoenolpyruvate CTP, cytidine triphosphate NADP, nicotinamide adenine dinucieotide phosphate GTP, guanosine triphosphate.

BL1643 was annotated to be a galactose 1-phosphate uridylyltransferase (EC 2.7.7.10) (GalT2), meaning the enzyme transfers the UMP (uridine monophosphate) unit of UTP (uridine triphosphate) to GallP. Although the LnpC protein did not have this activity, it showed UDP-glucose-hexose 1-phosphate uridylyltransferase... 

Fig. 20.5 The Leloir pathway of galactose metabolism and the uridine diphosphate (UDP) glucose pyrophosphorylase pathway. Gaik, galactokinase gait, galactose 1-phosphate uridyltrans-ferase gale, UDP-galactose 4-epimerase hex, hexokinase pgm, phosphoglucomutase Ugp, UDP-glucose pyrophosphorylase...

Figure 13.1 Lactose metabolism in lactic acid bacteria. GalK, galactokinase GalT, galactose-l-phosphate uridyltransferase GalE, UDP-galactose-4 -epimerase GalU, glucose-l-phosphate uridyltransferase UPD, uridine diphosphate.

The transformation of D-galactose 1-phosphate to D-glucose 1-phosphate has been shown to be catalyzed by an enzyme known as galactowaldenase. Leloir and cp-workers 103) demonstrated that the reaction required a coenzyme that was identified as uridine diphosphate glucose (sym-D-gluco-... 

This compound is the coenzyme for the conversion of galactose-1-phosphate into glucose-l-phosphate. The apoenzyme for this reaction occurs in yeast. Uridine diphosphate glucose has the following... 

Enzymatic synthesis of uridine diphosphate glucose has been observed, but there are no published reports on how the synthesis takes place. However, we do have some indication of how the compound may act as a coenzyme. When incubated with an extract of S. fragilis it is transformed into uridine diphosphate galactose. This would be a biological Walden inversion. Discovery of this reaction has led to the following hypothesis for the mechanism of the conversion of galactose-1-phosphate to glucose-l-phosphate ... 

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