Species: Pseudomonas fluorescens ACB
This enzyme is an extradiol-type dioxygenase that catalyzes the conversion of benzene-1,4-diol to (2E,4Z)-4-hydroxy-6-oxohexa-2,4-dienoate. It is a novel member of the nonheme-iron(II)-dependent dioxygenase family. It did not show any significant amino acid sequence identity with known dioxygenases [Moonen08a].
The native apparent molecular mass of this α2β2 heterotetrameric enzyme was determined by online size-exclusion chromatography/mass spectrometry to be 112.4 kDa, composed of an α subunit of 17.8 kDa and a β subunit of 38.3 kDa. The β subunit contains binding sites for Fe2+ and the competitive inhibitor 4-hydroxybenzoate. The spectral properties of the enzyme also suggested an extradiol-type dioxygenase [Moonen08].
Molecular Weight: 112.4 kD (experimental) [Moonen08]
Enzymatic reaction of: hydroquinone 1,2-dioxygenase
Synonyms: hydroquinone 1.2-dioxygenase
EC Number: 18.104.22.168benzene-1,4-diol + oxygen → (2Z,4E)-4-hydroxy-6-oxohexa-2,4-dienoate + H+
The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the direction in which it was curated.
The reaction is physiologically favored in the direction shown.
In Pathways: 4-hydroxyacetophenone degradation
The enzyme catalyzed the ring cleavage of a wide range of hydroquinone substrates to produce the corresponding 4-hydroxymuconic semialdehydes. Use of the competitive inhibitor 4-hydroxybenzoate during purification prevented irreversible inactivation of the enzyme [Moonen08].
The Km value was determined at pH 7.0, 25 °C. A variety of phenolic compounds inhibited the enzxyme [Moonen08].Activators (Unknown Mechanism): Fe2+ [Moonen08] Inhibitors (Competitive): 4-hydroxybenzoate (Kic = 14µM) [Moonen08] Inhibitors (Unknown Mechanism): 2,2'-dipyridyl [Moonen08], o-phenanthroline [Moonen08], hydrogen peroxide [Moonen08]Kinetic Parameters:
pH(opt): 7-8 [Moonen08]
Synonyms: HapD, hydroquinone dioxygenase β subunit
|Gene:||hapD||Accession Number: G-14992 (MetaCyc)|
Molecular Weight: 38.403 kD (from nucleotide sequence)
Unification Links: UniProt:B1GRL9
Synonyms: hydroquinone dioxygenase α subunit
|Gene:||HapC||Accession Number: G-14991 (MetaCyc)|
Molecular Weight: 17.841 kD (from nucleotide sequence)
Unification Links: UniProt:B1GRL8
Moonen08: Moonen MJ, Synowsky SA, van den Berg WA, Westphal AH, Heck AJ, van den Heuvel RH, Fraaije MW, van Berkel WJ (2008). "Hydroquinone dioxygenase from pseudomonas fluorescens ACB: a novel member of the family of nonheme-iron(II)-dependent dioxygenases." J Bacteriol 190(15);5199-209. PMID: 18502867
Moonen08a: Moonen MJ, Kamerbeek NM, Westphal AH, Boeren SA, Janssen DB, Fraaije MW, van Berkel WJ (2008). "Elucidation of the 4-hydroxyacetophenone catabolic pathway in Pseudomonas fluorescens ACB." J Bacteriol 190(15);5190-8. PMID: 18502868
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