Pyrophosphorylases

Flucytosine-resistant strains can develop very rapidly. These mutants may have a disturbed 5-FC-metabohsm, or a compensatory mechanism for the disturbed nucleic acid functions. No cytosine permease was found in a resistant Cyptococcus neoformans strain, whereas cytosine deaminase was absent in resistant C. albicans strains. A deficiency of uridine monophosphate pyrophosphorylase occurs frequently in resistant C. albicans strains (1). 

Sugar nucleotides are formed from sugar-l-phosphates and nucleoside triphosphates by specific pyrophosphorylase enzymes (Figure 23.18). For example, UDP-glucose pyrophosphorylase catalyzes the formation of UDP-glucose from glucose-l-phosphate and uridine 5 -triphosphate ... 

FIGURE 23.18 The UDP-glucose pyrophosphorylase reaction is a phosphoanhydride exchange, with a phosphoryl oxygen of glu-cose-l-P attacking the m-phosphorus of UTP to form UDP-glucose and pyrophosphate. 

In animal tissues the synthesis of UDPGlc from UTP and glucose-1-phosphate is catalysed by a pyrophosphorylase of widespread occurrence. With the enzyme from human liver, there is no specificity for either the... 

SWEETLOVE, L.J., BURRELL, M.M., AP REES, T., Starch metabolism in tubers of transgenic potato (Solanum tuberosum) with increased ADPglucose pyrophosphorylase, Biochem. J., 1996, 320,493-498. 

ZRENNER, R., WILLMITZER, L SONNEWALD, U., Analysis of the expression of potato uridinediphosphate-glucose pyrophosphorylase and its inhibition by antisense RNA, Planta, 1993,190, 247-252. 

Isselbacher (13, 14) has shown that mammalian liver and brain, but not red cells, contain an enzyme, UDPGal pyrophosphorylase, which catalyzes the following reaction ... 

Flavin Coenzymes.—5-Deazaflavin-adenine dinucleotide (2) can be prepared from the 5-deazaFMN,21 using a FAD pyrophosphorylase from rat liver.22 When the apoprotein of D-amino-acid oxidase from pig kidney is reconstituted with (2), no oxidation of D-alanine is observed, although the flavin chromophore in the reconstituted enzyme is reduced on the addition of DL-amino-acids.22 This has been interpreted as indicating that hydrogen transfer from the amino-acid to (2) can still... 

There is some difficulty in correlating results of PAN exposure in vfvo with the above types of in vitro studies. For example, UDP glucose pyrophosphorylase is very susceptible to PAN in vitro, but in vivo there is a stimulation of enzymatic activity (at 112 ppm for 6 min). It is also... 

Hall, M. A., and L. Ordin. Subcellular location of phosphoglucomutase and UDP glucose pyrophosphorylase in avena coleoptiles. Physiol. Plant. 20 624-633, I%7. 

This enzyme [EC 2.4.2.18], also referred to as phospho-ribosyl-anthranilate pyrophosphorylase, catalyzes the reaction of anthranilate with phosphoribosylpyrophos-phate to produce A-5 -phosphoribosylanthranilate and pyrophosphate. In certain species, this enzyme is part of a multifunctional protein, together with one or more other components of the system for the biosynthesis of tryptophan (i.e., indole-3-glycerol-phosphate synthase, anthranilate synthase, tryptophan synthase, and phos-phoribosylanthranilate isomerase). 

This enzyme [EC Unil], also known as ADP-glucose synthase and ADP-glucose pyrophosphorylase, catalyzes the reaction of a-o-glucose 1-phosphate with ATP to produce ADP-glucose and pyrophosphate. 

This enzyme [EC 2.4.2.17], also known as phosphoribo-syl-ATP pyrophosphorylase, catalyzes the reaction of ATP with 5-phospho-a-D-ribose 1-diphosphate to generate l-(5-phospho-D-ribosyl)-ATP and pyrophosphate. 

This enzyme [EC 2.5.1.15], also known as dihydro-pteroate pyrophosphorylase, catalyzes the reaction of 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteri-dine diphosphate with 4-ammobenzoate to produce pyrophosphate and dihydropteroate. 

This enzyme [EC 2.7.T.2], also known as FAD synthase and FAD pyrophosphorylase, catalyzes the ATP-depen-dent transfer of an adenylyl group to FMN to yield FAD and diphosphate. 

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