The Enzyme Database

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Accepted name: factor-independent urate hydroxylase
Reaction: urate + O2 + H2O = 5-hydroxyisourate + H2O2
For diagram of AMP catabolism, click here
Other name(s): uric acid oxidase; uricase; uricase II; urate oxidase
Systematic name: urate:oxygen oxidoreductase
Comments: This enzyme was previously thought to be a copper protein, but it is now known that the enzymes from soy bean (Glycine max), the mould Aspergillus flavus and Bacillus subtilis contains no copper nor any other transition-metal ion. The 5-hydroxyisourate formed decomposes spontaneously to form allantoin and CO2, although there is an enzyme-catalysed pathway in which EC, hydroxyisourate hydrolase, catalyses the first step. The enzyme is different from EC (FAD-dependent urate hydroxylase).
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, UM-BBD, CAS registry number: 9002-12-4
1.  London, M. and Hudson, P.B. Purification and properties of solubilized uricase. Biochim. Biophys. Acta 21 (1956) 290–298. [DOI] [PMID: 13363909]
2.  Mahler, H.R., Hübscher, G. and Baum, H. Studies on uricase. I. Preparation, purification, and properties of a cuproprotein. J. Biol. Chem. 216 (1955) 625–641. [PMID: 13271340]
3.  Robbins, K.C., Barnett, E.L. and Grant, N.H. Partial purification of porcine liver uricase. J. Biol. Chem. 216 (1955) 27–35. [PMID: 13252004]
4.  Kahn, K. and Tipton, P.A. Spectroscopic characterization of intermediates in the urate oxidase reaction. Biochemistry 37 (1998) 11651–11659. [DOI] [PMID: 9709003]
5.  Colloc'h, N., el Hajji, M., Bachet, B., L'Hermite, G., Schiltz, M., Prange, T., Castro, B. and Mornon, J.-P. Crystal structure of the protein drug urate oxidase-inhibitor complex at 2.05 Å resolution. Nat. Struct. Biol. 4 (1997) 947–952. [PMID: 9360612]
6.  Imhoff, R.D., Power, N.P., Borrok, M.J. and Tipton, P.A. General base catalysis in the urate oxidase reaction: evidence for a novel Thr-Lys catalytic diad. Biochemistry 42 (2003) 4094–4100. [DOI] [PMID: 12680763]
[EC created 1961, modified 2002, modified 2005, modified 2010]
Accepted name: FAD-dependent urate hydroxylase
Reaction: urate + NADH + H+ + O2 = 5-hydroxyisourate + NAD+ + H2O
Other name(s): HpxO enzyme; FAD-dependent urate oxidase; urate hydroxylase
Systematic name: urate,NADH:oxygen oxidoreductase (5-hydroxyisourate-forming)
Comments: A flavoprotein. The reaction is part of the purine catabolic pathway in the bacterium Klebsiella pneumoniae. The enzyme is different from EC, factor-independent urate hydroxylase, found in most plants, which produces hydrogen peroxide. The product of the enzyme is a substrate for EC, hydroxyisourate hydrolase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
1.  O'Leary, S.E., Hicks, K.A., Ealick, S.E. and Begley, T.P. Biochemical characterization of the HpxO enzyme from Klebsiella pneumoniae, a novel FAD-dependent urate oxidase. Biochemistry 48 (2009) 3033–3035. [DOI] [PMID: 19260710]
[EC created 2010]
Accepted name: 1,3,7-trimethyluric acid 5-monooxygenase
Reaction: 1,3,7-trimethylurate + NADH + H+ + O2 = 1,3,7-trimethyl-5-hydroxyisourate + NAD+ + H2O
Glossary: isourate = 1,3,5,7-tetrahydropurine-2,6,8-trione
Other name(s): tmuM (gene name)
Systematic name: 1,3,7-trimethylurate,NADH:oxygen oxidoreductase (1,3,7-trimethyl-5-hydroxyisourate-forming)
Comments: The enzyme, characterized from the bacterium Pseudomonas sp. CBB1, is part of the bacterial C-8 oxidation-based caffeine degradation pathway. The product decomposes spontaneously to a racemic mixture of 3,6,8-trimethylallantoin. The enzyme shows no acitivity with urate. cf. EC, FAD-dependent urate hydroxylase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
1.  Mohanty, S.K., Yu, C.L., Das, S., Louie, T.M., Gakhar, L. and Subramanian, M. Delineation of the caffeine C-8 oxidation pathway in Pseudomonas sp. strain CBB1 via characterization of a new trimethyluric acid monooxygenase and genes involved in trimethyluric acid metabolism. J. Bacteriol. 194 (2012) 3872–3882. [DOI] [PMID: 22609920]
2.  Summers, R.M., Mohanty, S.K., Gopishetty, S. and Subramanian, M. Genetic characterization of caffeine degradation by bacteria and its potential applications. Microb. Biotechnol. 8 (2015) 369–378. [DOI] [PMID: 25678373]
[EC created 2016]
Accepted name: hydroxyisourate hydrolase
Reaction: 5-hydroxyisourate + H2O = 5-hydroxy-2-oxo-4-ureido-2,5-dihydro-1H-imidazole-5-carboxylate
For diagram of AMP catabolism, click here
Other name(s): HIUHase; 5-hydroxyisourate hydrolase
Systematic name: 5-hydroxyisourate amidohydrolase
Comments: The reaction is the first stage in the conversion of 5-hydroxyisourate into S-allantoin. This reaction will also occur spontaneously but more slowly.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 255885-20-2
1.  Raychaudhuri, A. and Tipton, P.A. A familiar motif in a new context: the catalytic mechanism of hydroxyisourate hydrolase. Biochemistry 42 (2003) 6848–6852. [DOI] [PMID: 12779339]
2.  Raychaudhuri, A. and Tipton, P.A. Cloning and expression of the gene for soybean hydroxyisourate hydrolase. Localization and implications for function and mechanism. Plant Physiol. 130 (2002) 2061–2068. [DOI] [PMID: 12481089]
3.  Sarma, A.D., Serfozo, P., Kahn, K. and Tipton, P.A. Identification and purification of hydroxyisourate hydrolase, a novel ureide-metabolizing enzyme. J. Biol. Chem. 274 (1999) 33863–33865. [DOI] [PMID: 10567345]
[EC created 2004]

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