Uronic acids enzyme catalyzing

Enzyme-catalyzed oxidation of the primary alcohol at carbon 6 of a hexose yields a uronic acid. Enzyme-catalyzed oxidation of D-glucose, for example, yields D-glucuronic acid, shown here in both its open-chain and cyclic hemiacetal forms ... 

At the time of writing of the earlier article,1 compounds in this class had been prepared only from hexuronic acid derivatives by base- or enzyme-catalyzed eliminations methyl (methyl 4-deoxy-/3-L-threo-hex-4-enopyranosid)uronate (73), for example, had been pre-... 

The most important mammalian conjugation molecules for pollutants and their metabolites are uronic acids, glutathione, amino acids, taurine, and sulphate. The conjugation is catalyzed by liver enzymes like UDP-glucuronyl-transferases, sulfotransferases, glutathione S-transferases and amino acid N-acyltransferases. 

Enzyme-catalyzed hydrolysis of polysaccharides containing uronic acids is well established, but, during the past few years, it has become evident that bacterial enzymes may degrade such materials by a process involving eliminations and the production of oligosaccharides containing nonreducing, terminal, 4,5-unsaturated, uronic acid residues. 

D-Glucosiduronic acids are of rare occurrence in plants, although in those species where they do occur they sometimes accumulate in high concentration. The mechanism of their formation in plants is undoubtedly identical with that in animals. An enzyme preparation from leaves of the French bean has been shown to catalyze the formation of quercetin-3-yl /3-D-glucopyranosiduronic acid from uridine 5-(a-D-glucopyranosyl-uronic acid pyrophosphate) and quercetin. In contrast to the liver enzyme, the transferase from beans was found to be specific for the acceptor. 

These /8-elimination reactions, which were proved for n-glucopyran-uronate derivatives, belong to the class of axialr-equatorial reactions (type B). This type of enolacetal-forming, /8-elimination reaction is found in the enzyme-catalyzed degradation of hyaluronic acid and chondroitin 4- and 6-sulfates. 

Direct oxidation of CH2OH in the presence of CH=0 is not practical, so laboratory preparations of uronic acids are limited to processes that include appropriate protection-deprotection strategies. D-Glucuronic acid, an intermediate in the biosynthesis of vitamin C and in various metabolic pathways, is biosynthesized by an enzyme-catalyzed NAD oxidation of a derivative of D-glucose. 

Enzyme-catalyzed oxidation of the terminal —CH2OH group of a monosaccharide to a COOH group gives a uronic acid. 

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