Uridine diphosphate, UDP glucose

From extensive analysis of recombinant proteins, and the crystal structure of A. thaliana protein, detailed reaction mechanisms have been proposed. The ANS reaction likely proceeds via stereospecific hydroxylation of the leucoanthocyanidin (flavan-3,4-cA-diol) at the C-3 to give a flavan-3,3,4-triol, which spontaneously 2,3-dehydrates and isomerizes to 2-flaven-3,4-diol, which then spontaneously isomerizes to a thermodynamically more stable anthocyanidin pseudobase, 3-flaven-2,3-diol (Figure 3.2). The formation of 3-flaven-2,3-diol via the 2-flaven-3,4-diol was previously hypothesized by Heller and Forkmann. The reaction sequence, and the subsequent formation of the anthocyanidin 3-D-glycoside, does not require activity of a separate dehydratase, which was once postulated. Recombinant ANS and uridine diphosphate (UDP)-glucose flavonoid 3-D-glucosyltransferase (F3GT, sometimes... 

In the third step, glucose-1-phosphate is converted to uridine diphosphate (UDP) glucose, the immediate precursor of glycogen synthesis, by reaction with uridine triphosphate (UTP). This reaction is catalyzed by glucose-1-phosphate uridylyltransferase (or UDP-glucose pyrophos-phorylase) ... 

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...

Transmission electron microscopy (TEM) of cellulose-producing bacterial cells shows the presence of pores in the outer membrane of these cells. It is believed that bacterial cellulose is produced from uridine diphosphate (UDP)-glucose (its immediate... 

Glucose 1-phosphate then is coupled with uridine diphosphate (UDP) to form UDP-glucose, the main donor of glucosyl residues during the construction of glycogen. 

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. 

UDP uridine diphosphate UDP-galactose uridine diphosphate galactose UDP-glucose uridine diphosphate glucose UMP uridine monophosphate UTP uridine triphosphate Val valine... 

Thus in this reaction the donor glucose molecule is activated as its uridine diphosphate (UDP) derivative. A similar example is given by the synthesis of N-acetyllactosamine (37) using galactosyl transferase (Scheme 5.31). 

UDP-glucose is an activated form of glucose involved in the synthesis of glycogen. It is a nucleotide in which a-D-glucose is esterified at C-1 by the terminal phosphate of uridine diphosphate (UDP). From this description, draw the structure of UDP-glucose. 

Recently, a universal enzyme-coupled fluorescence assay for glycosyl transferases was developed. This method is extremely cost-effective and is based on the quantification of nucleotides produced in the glycosyl transfer reaction. The guanosine diphosphate (GDP), uridine diphosphate (UDP), and cytidine monophosphate (CMP) are phos-phorylated with nucleotide kinase in the presence of excess of ATP, generating ADP. Via coupled enzyme reactions involving ADP-hexokinase,glucose-6-phosphate dehydrogenase, and diaphorase, the ADP is utilized for the conversion of resazurin to resorufin, which is then quantified by fluorescence measurement. 

---