Reaction: 4-methylphenol + 4 oxidized azurin + H2O = 4-hydroxybenzaldehyde + 4 reduced azurin + 4 H+ (overall reaction)
(1a) 4-methylphenol + 2 oxidized azurin + H2O = 4-hydroxybenzyl alcohol + 2 reduced azurin + 2 H+
(1b) 4-hydroxybenzyl alcohol + 2 oxidized azurin = 4-hydroxybenzaldehyde + 2 reduced azurin + 2 H+
Glossary: 4-methylphenol = 4-cresol = p-cresol
Other name(s): pchCF (gene names); p-cresol-(acceptor) oxidoreductase (hydroxylating); p-cresol methylhydroxylase; 4-cresol dehydrogenase (hydroxylating)
Systematic name: 4-methylphenol:oxidized azurin oxidoreductase (methyl-hydroxylating)
Comments: This bacterial enzyme contains a flavin (FAD) subunit and a cytochrome c subunit. The flavin subunit abstracts two hydrogen atoms from the substrate, forming a quinone methide intermediate, then hydrates the latter at the benzylic carbon with a hydroxyl group derived from water. The protons are lost to the bulk solvent, while the electrons are passed to the heme on the cytochrome subunit, and from there to azurin, a small copper-binding protein that is co-localized with the enzyme in the periplasm. The first hydroxylation forms 4-hydroxybenzyl alcohol; a second hydroxylation converts this into 4-hydroxybenzaldehyde.
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:
References:
1. Hopper, D.J. and Taylor, D.G. The purification and properties of p-cresol-(acceptor) oxidoreductase (hydroxylating), a flavocytochrome from Pseudomonas putida. Biochem. J. 167 (1977) 155-162. [PMID: 588247]
2. McIntire, W., Edmondson, D.E. and Singer, T.P. 8α-O-Tyrosyl-FAD: a new form of covalently bound flavin from p-cresol methylhydroxylase. J. Biol. Chem. 255 (1980) 6553-6555. [PMID: 7391034]
3. Hopper, D.J., Jones, M.R. and Causer, M.J. Periplasmic location of p-cresol methylhydroxylase in Pseudomonas putida. FEBS Lett. 182 (1985) 485-488. [PMID: 3920077]
4. Bossert, I.D., Whited, G., Gibson, D.T. and Young, L.Y. Anaerobic oxidation of p-cresol mediated by a partially purified methylhydroxylase from a denitrifying bacterium. J. Bacteriol. 171 (1989) 2956-2962. [PMID: 2722739]
5. Reeve, C.D., Carver, M.A. and Hopper, D.J. Stereochemical aspects of the oxidation of 4-ethylphenol by the bacterial enzyme 4-ethylphenol methylenehydroxylase. Biochem. J. 269 (1990) 815-819. [PMID: 1697166]
6. Peters, F., Heintz, D., Johannes, J., van Dorsselaer, A. and Boll, M. Genes, enzymes, and regulation of para-cresol metabolism in Geobacter metallireducens. J. Bacteriol. 189 (2007) 4729-4738. [PMID: 17449613]
7. Johannes, J., Bluschke, A., Jehmlich, N., von Bergen, M. and Boll, M. Purification and characterization of active-site components of the putative p-cresol methylhydroxylase membrane complex from Geobacter metallireducens. J. Bacteriol. 190 (2008) 6493-6500. [PMID: 18658262]