Nucleoside phosphorylase and

Phosphatases and nucleotidases Nucleoside phosphorylases and hydrolases Deaminases Oxidases Summary... 

Shin et al. [88] Ornithine Kuruma prawn Ornithine carbamyl transferase, nucleoside phosphorylase and xanthine oxidase/in membranes prepared from cellulose triacetate, glutaraldehyde and 1,8-diamino-4-am i nomethyl octane Oxygen electrode ... 

Fedorov A, Shi W, Kicska GA, Fedorov E, Tyler PC, Furneaux RH, Hanson JC, Gainsford GJ, Larese JZ, Schramm VL, Almo SC (2001) Transition state structure of purine nucleoside phosphorylase and principles of atomic motion in enzymatic catalysis. Biochemistry 40 853-860... 

In some cases the combination of two biocatalysts in a multistep process allows, in an indirect manner, the preparation of some compounds or increases in their yields. Thus, Scheme 10.21 shows that the synthesis of a nucleoside analog containing a hypoxanthine base takes place in a two-step fashion using a combination of both nucleoside phosphorylase and adenine deaminase, obtaining the final analog in high yield. However, the direct preparation of this compound with hypoxanthine takes place with a very low yield due to the low solubility of this base [48]. 

Finally, the serum sample was incubated with the enzyme purine nucleoside phosphorylase and rechromatographed (Fig. 14C). From the disappearance of the inosine peak and the appearance of a peak with the retention time of hypoxanthine, it can be concluded that the peak under investigation was indeed inosine. 

A quantitatively less significant salvage pathway uses purine nucleoside phosphorylase and nucleoside kinase ... 

Pyrimidines derived from dietary or endogenous sources are salvaged efficiently in mammalian systems. They are converted to nucleosides by nucleoside phosphorylases and then to nucleotides by appropriate kinases. 

As a final note, there is the observation that antiviral agents act to inhibit the replication of nucleic acids. There is a connection with anticancer agents, which are enzyme inhibitors for DNA processes. In a way, the connection is obvious, in view of the fact that viruses are but pieces of DNA. A search of Medline indicates that antiviral agents being cUnically tested include inhibitors for the enzymes called nucleoside phosphorylases and M-deoxyribosylttansferases. 

The term carbocyclic nucleoside [181] is used to describe a group of compounds structurally related to nucleosides in which the furanose ring has been replaced by a cyclopentane ring. A consequence of this substitution is an enhancement of the metabolic stability of the carbocyclic nucleosides, which are not subjected to the action of nucleoside phosphorylases and hydrolases that cleave normal nucleosides. However, from the conformational point of view the tetrahydro-furan and cyclopentane rings are similar. Thus, carbocyclic nucleosides may act as substrates or inhibitors of the enzymes that activate (kinases) and transform nucleosides and nucleotides in living cells and incorporate them into DNA. Most approaches to the synthesis of carbocyclic nucleosides begin with the construction of the nucleic acid base from a functionalized cyclopentylamine, which with some exceptions is obtained as a racemic mixture. The medicinal chemistry of carbocyclic nucleosides, as well as the synthesis of the intermediate cyclopentylamines have been reviewed [181]. This section deals only with work published after that review, directly related with anti-AIDS research. 

The branched-chain compound 27 has been synthesized from 28 (available from D-mannose) by reductive amination then acid-catalysed hydrolysis. Compounds 27 thus prepared together with related compounds were tested for their inhibition against human blood purine nucleoside phosphorylase and a- and P-glucosidases. ... 

N. and deoxynucleosides can be synthesized via a Salvage pathway (see). TTiey are also produced by hydrolysis of nucleic acids and nucleotides. Nucleoside phosphorylases and deoxynucleoside phosphorylases catalyse the reversible, phosphate-dependent cleavage of N. and deoxyribonucleosides, forming ribose 1-phosphate or deoxyribose 1-phosphate and the free base. N. and deoxyribonucleosides can be converted into their corresponding nucleotides by the action of specific kinases. 

The possibility has been considered that purine bases can be converted to ribonucleosides by purine nucleoside phosphorylase, and thence to ribonucleotides by the purine nucleoside kinases. 

Pyrimidine ribonucleotides, like those of purines, may be synthesized de novo from amino acids and other small molecules (Chapter 11). Preformed pyrimidine bases and their ribonucleoside derivatives, derived from the diet of animals or found in the environment of cells, may be converted to ribonucleotides via nucleoside phosphorylases and nucleoside kinases. In some cells a more direct pyrimidine phosphoribosyltransferase pathway has also been recognized (Chapter 12). Ribonucleotides are catabolized by dephosphorylation, deamination, and cleavage of the glycosidic bond, to uracil. Uracil may be either oxidatively or reductively cleaved, depending on the organism involved, and can be converted to CO and NH (Chapter 13). 

A means of converting free bases into deoxyribonucleotides would appear to be afforded by the sequential action of nucleoside phosphorylases and kinases however, cells have only a very limited capability for the endogenous formation of the deoxyribose 1-phosphate needed for this... 

Purine nucleoside phosphorylase and thymidine phosphorylase have been shown to catalyze transfer of the deoxyribosyl group from one base to another by reaction sequences that involve the intermediate formation of free deoxyribose 1-phosphate by the following mechanism ... 

Purine-pyrimidine deoxyribosyl transfer reactions result when reactions (1) and (2) are catalyzed by the joint actions of purine nucleoside phosphorylase and thymidine phosphorylase, that is, when the activities of these enzymes are coupled. For example, the following reaction is catalyzed by extracts of human leukocytes (18) ... 

Coupling of purine nucleoside phosphorylase and thymidine phosphorylase in proliferating E. coli cells is demonstrated in the data of Fig. 

ADENOSINE DEAMINASE, PURINE NUCLEOSIDE PHOSPHORYLASE AND 5"-NUCLEOTIDASE ACTIVITIES IN INFECTIOUS MONONUCLEOSIS... 

These studies have identified quantitative variation of purine nucleoside phosphorylase which is heritable and stable within inbred mouse lines. Associated with the quantitative variability are electrophoretic differences between DBA/2J and C57BL/6J purine nucleoside phosphorylase and minor differences in thermal stability and affinity for nucleoside substrates. Additional studies are underway to characterize the gene products of these strains and map the Np-2 locus. 

Investigations undertaken early in the course of clinical studies of allopurinol established the predominance of oxipurinol (alloxanthine) among its metabolites. However, one patient to whom C-allopurinol had been given excreted a significant amount of a presumptive allopurinol ribonucleoside [1]. Somewhat later this ribonucleoside was synthesized chemically, and enzymatically by purine nucleoside phosphorylase, and was identified as 1-ribosyl-allopurinol (Fig. 1, 1)[2]. With oxipurinol as substrate the corresponding 1-ribosyloxipurinol (Fig. 1, II) was obtained, and by using uridine phosphorylase a third ribonucleoside, oxipurinol-7-ribonucleoside was prepared. Meanwhile a third metabolite had been isolated from the urine of treated patients, and the availability of reference substances made it possible to identify this as 7-ribosyl-oxipurinol (Fig. 1, III). 

Nicotinic Add Metabolism. The sequence of reactions leading to the formation of pyridine compounds is of particular interest as a source of nicotinic acid. Nutritional, isotopic, and genetic experiments have all shown that tryptophan and its metabolic derivatives including 3-hydroxy-anthranilic acid are precursors of nicotinic acid in animals and in Neuro-spora. The terminal steps in this sequence are not known. Under certain physiological conditions an increase in picolinic carboxylase appears to reduce nicotinic acid synthesis. This implies a common pathway as far as the oxidation of 3-hydroxyanthranilic acid. Whether quinolinic acid is a precursor of nicotinic acid is still uncertain. The enzyme that forms the amide of nicotinic acid also has not been isolated. Subsequent reactions of nicotinamide include the formation of the riboside with nucleoside phosphorylase and methylation by nicotinamide methyl-kinase. In animals W-methylnicotinamide is oxidized to the corresponding 6-pyridone by a liver flavoprotein. Nicotinic acid also forms glycine and ornithine conjugates. Both aerobic and anaerobic bacteria have been found to oxidize nicotinic acid in the 6-position. ... 

Enzyme electrode-FIA Orthophosphate 3 0.1 Amperometric detection of H2O2 produced by interaction of phosphate with coimmobilized nucleoside phosphorylase and xanthine oxidase [123]... 

While potentiometric enzymatic electrodes for detection of phosphate have been developed [121,122], no application has been made of these to water analysis because of the relatively poor sensitivity. However, amperometric enzyme electrodes have been reported that they have high sensitivity, selectivity, and long operational life and it is expected that the use of these for water analysis will become more widespread (see Table 8.2). For example, a sensitive enzyme electrode based on the amperometric detection of hydrogen peroxide produced by membrane coimmobilized nucleoside phosphorylase and xanthine oxidase has been reported for the detection of phosphate by D Urso and Coulet [123]. Other similar enzyme electrode systems suitable for water analysis are listed in Table 8.2. 

Enzymatic synthesis of 3 -fluoro-2, 3 -dideoxyguanosine (3 -F-2, 3 -dGuo) - a potential chemical therapy agent for treatment of viral infections was accomplished using nucleoside phosphorylases and adenosine deaminase from E. coli. 

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