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Biotransformation xanthine oxidase

The bioavailability of azathioprine (80%) is superior to 6-MP (50%). After absorption azathioprine is rapidly converted by a nonenzymatic process to 6-MP. 6-Mercaptopurine subsequently undergoes a complex biotransformation via competing catabolic enzymes (xanthine oxidase and thiopurine methyltransferase) that produce inactive metabolites and anabolic pathways that produce active thioguanine nucleotides. Azathioprine and 6-MP have a serum half-life of less than 2 hours however, the... [Pg.1327]

Quinazoline is oxidized rapidly by xanthine oxidase to quinazolin-4(3//)-one which subsequently is oxidized more slowly to quinazoline-2,4(l//,3//)-dione. Quinazoline is also oxidized to quinazolin-4(3//)-one by rabbit liver aldehyde oxidase but the reaction ceases within a short time it appears that quinazoline is able to inactivate the aldehyde oxida.se, Quinazolin-4(3//)-one is rapidly oxidized by aldehyde oxidase to quinazoline-2,4(l//,3//)-dione. Various 6-substituted and 6,7-disubstituted quinazolin-4(3//)-ones are quantitatively oxidized to the respective quinazoline-2,4(l//,3//)-diones by buttermilk xanthine o.xidase, ° Biotransformation of quinazoline by a mutant strain of the bacterium Pseudomonas putida gives quinazolin-4(3//)-one, c(s-5,6-dihydroquinazoline-5,6-diol, and cis-5,6,7,8-tetrahydroquinazoline-5,6-di-... [Pg.110]

Shanmuganathan, K., Koudriakova, T., Nampalli, S., et al. (1994) Enhanced brain delivery of an anti-HIV nucleoside 2 -F-ara-ddI by xanthine oxidase mediated biotransformation. J. Med. Chem., 37, 821-827. [Pg.195]

Of the Phase I reactions, oxidative biotransformations are by far the most common. These reactions are carried out by several oxidative enzyme systems, the most predominant of which is the CYP superfamily of enzymes. Additional oxidative enzymes include FMO, xanthine oxidase, aldehyde oxidase, alcohol and aldehyde dehydrogenases monoamine oxidases, and various peroxidases. Determining the enzyme(s) employed to biotransform any particular substrate will depend on the substrates chemical and physical characteristics as well as functional substituents. This chapter does not describe in detail the mechanism of these various enzymes however, it does illustrate the product(s) (i.e., metabolites) produced by each reaction. [Pg.281]

Bhushan B et al., Mechanism of xanthine oxidase catalyzed biotransformation of HMX under anaerobic conditions, Biochem. Biophys. Res. Comun., 306, 509, 2003. [Pg.226]

Amongst mammals, xanthine oxidase levels appear to be less variable than aldehyde oxidase, with the highest activity for the former enzyme observed in dog, rat and cat (see Table 3.2). This is convenient for those drugs which are potential substrates for the enzyme, as dog and rat are the species routinely employed for metabolism and toxicity studies. For example, 6-mercaptopurine undergoes substantial biotransformation to 6-thiouric acid in both man and rat [116-118]. [Pg.101]

Other oxidative enzymes, though certainly important in the biotransformation of some drugs (e.g., xanthine oxidase contributes to the overall metabolism of substances such as caffeine and theophylline), are not responsible for the metabolism for very many drugs compared to the GYP enzymes. [Pg.170]

Oxidations are the most common biotransformation reactions that occur with most drugs. There are several classes of enzymes that carry out these reactions cytochrome P450s, flavin monooxygenases, monoamine oxidases, xanthine oxidase, aldehyde oxidases, aldehyde dehydrogenases, and peroxidases. Typical reactions and substrate substructures for each of these classes of enzymes will be described. [Pg.16]

Adenosine formation is accelerated under hypoxic conditions (Rudolphi et al. 1992), but it is metabohsed only after reperfusion. Now superoxide dismutase and catalase are insufficient to serve detoxification of the reactive oxygen species resulting from the biotransformation of hypoxanthine to xanthine and of xanthine to uric acid. While xanthine oxidase inhibitors as oxypurinol do protect against ischaemic damage (Helfman and Phillis 1989, Lin and Phillis 1992), adenosine deaminase inhibitors as trazodone (Sheid 1985) are expected to reduce the formation of hypoxanthine and xanthine, the substrates for xanthine oxidase. [Pg.489]

Rajagopalan KV. Xanthine dehydrogenase and aldehyde oxidase. In Guengerich FP, (editor). Biotransformation, Vol. 3, Comprehensive Toxicology, first ed. Elsevier Science, Oxford 1997. p 165-178. [Pg.34]


See other pages where Biotransformation xanthine oxidase is mentioned: [Pg.97]    [Pg.294]    [Pg.88]    [Pg.234]    [Pg.237]    [Pg.1659]    [Pg.234]    [Pg.237]    [Pg.3365]    [Pg.1480]    [Pg.23]    [Pg.88]    [Pg.559]    [Pg.98]    [Pg.3]   
See also in sourсe #XX -- [ Pg.158 , Pg.159 ]




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Oxidases xanthine oxidase

Xanthin

Xanthine

Xanthins

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