Phenol hydroxylases

Interestingly, an additional component is associated with DMP phenol hydroxylase, the so-called auxiliary protein DmpK, which seems to be responsible for the iron-dependent assembly of DmpLNO [171]. More specifically, DmpK has been proposed to play a significant role during the post-translational incorporation of iron into apoDmpLNO. DmpK appears to be unique amongst binuclear nonheme iron oxygenases. 

NATASA Mine, GERHARD SCHENK AND GRAEME R. HANSON 

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The metabolism of fluorophenols by phenol hydroxylase from Trichosporium cutaneum, catechol 1,2-dioxygenase from Pseudomonas arvilla strain C-1, and by the fungus Exophilia jeanselmei has been examined, and detailed NMR data were given for the ring fission flnoromnconates (Boersma et al. 1998). 

Peelen S, IMCM Rietjens, WJH van Berkel, WAT van Workum, 1 Vervoort (1993) F-NMR study on the pH-dependent regioselectivity and rate of the ort/jo-hydroxylation of 3-fluorophenol hy phenol hydroxylase from Trichosporon cutaneum. Eur J Biochem 218 345-353. 

Kirchner U, AH Westphal, R Muller, WJH van Berkel (2003) Phenol hydroxylase from Bacillus thermoglucosi-dasius A7, a two-component monooxygenase with a dual role for PAD. J Biol Chem 278 47545-47553. 

The metabolism of a range of fluorophenols containing up to five fluorine substituents was examined using phenol hydroxylase from Trichosporon cutaneum (Peelen et al. 1995). Fluorocatechols were formed, with loss of fluoride for some substrates. 

Fluorinated Muconates Formed from Fluorophenols by Phenol Hydroxylase and Catechol 1,2-Dioxygenase from Exophilia jeanselmei Fluoromuconate Metabolite Phenolic Substrate(s)... 

PHENOL HYDROXYLASE CATECHOL 1,2-DIOXYGENASE CATECHOL 2,3-DIOXYGENASE CATECHOL O-METHYLTRANSFERASE CATECHOL OXIDASE... 

NITRATE REDUCTASE NITRITE REDUCTASE PHENOL HYDROXYLASE PROLINE DEHYDROGENASE PUTRESCINE OXIDASE PYRUVATE OXIDASE SALICYLATE 1-MONOOXYGENASE SUCCINATE DEHYDROGENASE SULFITE REDUCTASE XANTHINE OXIDASE Falling ball viscometry,... 

NAD(P)H DEHYDROGENASE (QUINONE) NITRIC OXIDE SYNTHASE PHENOL HYDROXYLASE PROTOCHLOROPHYLLIDE REDUCTASE SQUALENE SYNTHASE SULFITE REDUCTASE NADPH diaphorase,... 

PHENOL HYDROXYLASE PHENYLALANINE MONOOXYGENASE PLASMANYLETHANOLAMINE A -DESA-TURASE... 

PHENYLALANINE DECARBOXYLASE PHENOL HYDROXYLASE Phenol 2-monooxygenase,... 

Two different diiron centres have been characterized by Mossbauer and EPR spectroscopies in the oxygenase part of phenol hydroxylase from Pseudomonas. In one centre the irons were suggested to be oxo-bridged whereas for the other a hydroxo bridge was preferred.170... 

Shingler, V., Franklin, F. C., Tsuda, M., Halroyd, D. Bagdasarian, M. (1989). Molecular analysis of a plasmid-encoded phenol hydroxylase from Pseudomonas CF600. Journal of General Microbiology, 135, 1083—92. 

Ridder, L., Mulholland, A.J., Rietjens, I.M.C.M., and Vervoot, J., A quantum mechanical/molecular mechanical study of the hydroxylation of phenol and halogenated derivatives by phenol hydroxylase, J. Am. Chem. Soc., 122, 8728-8738, 2000. 

Modelling can pinpoint functional groups and analyse catalytic interactions. In several enzymes, catalytic interactions have been identified via calculation. For example, in the flavin-dependent monooxygenases, para-hydroxybenzoate hydroxylase and phenol hydroxylase, a conserved proline residue was found from QM/MM modelling, which specifically stabilizes the transition state for aromatic hydroxy-lation.12,13... 

Mathematical models of benzene and phenol metabolism suggest that the inhibition by benzene of phenol metabolism, and by phenol on benzene metabolism, occurs through competition for a common reaction site, which can also bind catechol and hydroquinone (Schlosser et al. 1993). Flavonoids have been shown to inhibit phenol hydroxylase or increase phenol hydroxylase activity in a dose-dependent manner, dependent on the oxidation potential of the flavonoid (Hendrickson et al. 1994). 

PHBH is the protype of the flavoprotein aromatic hydroxylases. Each subunit of this dimeric enzyme contains two active sites which, during catalysis, are alternately visited by the isoalloxazine ring of the FAD cofactor (31). Catalysis is iiutiated by reduction of the flavin in the exterior active site. The reduced flavin then moves to the interior active site where the reactions with oxygen occur. A similar conformational flexibility of the FAD cofactor has been observed in the crystal structures of phenol hydroxylase (EC 1.14.13.7) and 3-hydroxybenzoate 4-hydroxylase (EC 1.14.13.23). PHBH obeys the following kinetic mechanism ... 

Enroth C, Neujahr H, Schneider G, Lindqvist Y. The crystal structure of phenol hydroxylase in complex with EAD and phenol provides evidence for a concerted conformational change in the enzyme and its cofactor during catalysis. Structure 1998 6 605-617. 

However, the activated, protonated C(4a)-hydroperoxyflavin is not by itself a powerful oxidizing species. From detailed biochemical studies on the catalytic mechanism of such enzymes, especially para-hydroxybenzoate hydroxylase (PHBH) and phenol hydroxylase (PH), it appears that not only the peroxyflavin needs to be activated through protonation of the distal oxygen, but also the phenolic substrates require activation in order to obtain substrate conversion. This substrate activation is achieved through deprotonation of the hydroxyl moiety of the phenolic substrate. The active site of PHBH, for example, shows a tyrosine network consisting of tyrosines 385 and 201 (Fig. 4.82) responsible for this deprotonation and activation of the substrate. 

For the determination of phenols and amines enzymes with low selectivity, e.g. laccase, horseradish peroxidase, tyrosinase, and polyphenol oxidase, as well as specific enzymes, e.g. phenol hydroxylase and catechol-1,2-oxygenase, can be used in biosensors. 

Phenol-2-hydroxylase also oxidizes NADPH with the formation of H2O2. Various monosubstituted phenols are also oxidized, but at a lower rate than phenol itself. Therefore the sensitivity of phenol hydroxylase enzyme electrodes based on O2 indication as described by Kjellen and Neujahr (1980) is different for substituted and unsubstituted phenols. Consequently, in mixtures of phenols the oxygen consumption does not reflect the real phenol concentration. 

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