Guanosine diphosphate-glucose

Figure 47-7. Pathway of biosynthesis of dolichol-P-P-oligosaccharide. The specific linkages formed are indicated in Figure 47-8. Note that the first five internal mannose residues are donated by GDP-mannose, whereas the more external mannose residues and the glucose residues are donated by dolichol-P-mannose and dolichol-P-glucose. (UDP, uridine diphosphate Dol, dolichol P, phosphate UMP, uridine monophosphate GDP, guanosine diphosphate M, mannose G, glucose.)...

Uridine-diphosphate-glucose (UDPG) Guanosine 5 -diphosphate-3 -diphosphate C15H24N2O17P2 (566.3) 10.9 7.5 1 1 ... 

Glucose 6-phosphate Inorganic pyrophosphate Inosine diphosphate Guanosine diphosphate Uridine diphosphate... 

ADP-hexoses D-glucose, D-mannose, D-galactose ADP-mannitol Guanosine diphosphate-X... 

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. 

Fig. 20.1. Abbreviated scheme of the synthesis of a diantennary N-glycan. Fucose modification has been omitted. 20.1, Phosphomannomutase 2 (PMM2) 20.2, phosphoman-nose isomerase (PMI) 20.3, glucosyltransferase I (GT I) 20.4, mannosyltransferase VI (MT VI) 20.5, dolichol phosphate-mannose synthase-1 (DPM synthase-1) 20.5, N-acet-ylglucosaminyltransferase II (GnT II) 20.7, glucosidase I (G I) GDP, guanosine diphosphate Marly mannose GlcNACy N-acetylglucosamine Do/, dolichol P, phosphate G/c, glucose Gal galactose SiUy sialic acid. Dotted arrow indicates multiple steps...

In addition to their role as components of nucleoproteins, purines and pyrimidines are vital to the proper functioning of the cell. The bases are constituents of various coenzymes, such as coenzyme A (CoA), adenosine triphosphate (ATP), guanosine triphosphate (GTP), cytidine triphosphate (CTP), diphosphopyridine nucleotide (DPN), triphosphopyridine nucleotide (TPN), and flavin adenine dinucleotide (FAD). A pyrimidine derivative, cytidine diphosphate choline, is involved in phospholipid synthe another pyrimidine compound, uridine diphosphate glucose, is an important substance in carbohydrate metabolism. Cytidine diphosphate ribitol functions in the biosynthesis of a new group of bacterial cell-wall components, the teichoic acids. While mammals excrete nitrogen derived from protein catabolism in the form of urea, birds eliminate their nitrogen by synthesizing it into the purine compound, uric acid. 

Other nucleoside diphosphate sugar compounds are known, eg, UDPGal. In addition, the same sugar may be linked to different nucleotides. For example, glucose may be linked to uridine (as shown above) as well as to guanosine, thymidine, adenosine, or cy-tidine nucleotides. 

This enzyme [EC 2.7.7.28], also known as NDP-hexose pyrophosphorylase, catalyzes the reaction of a nucleoside triphosphate with a hexose 1-phosphate to produce a NDP-hexose and pyrophosphate (or, diphosphate). In the reverse reaction the NDP-hexose can be, in decreasing order of activity, guanosine, inosine, and adenosine diphosphate hexoses in which the sugar is either glucose or mannose. 

Guanosine, inosine and adenosine diphosphate hexoses are substrates in the reverse reaction with either glucose or mannose as the sugar.]... 

L-fucose, D-rhamnose GDP-D-mannuronic acid GDP-4-keto-6-deoxy-D-mannose P, P -Diguanosine tetraphosphate P, P -Diguanosine triphosphate Guanosine tetraphosphate Cytidine diphosphate-X CDP-D-glucose CDP-L-ribitol... 

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