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J. Bacteriol., Nov 1997, 6680-6687, Vol 179, No. 21
MH Eppink, SA Boeren, J Vervoort and WJ van Berkel
A novel flavoprotein monooxygenase, 4-hydroxybenzoate 1-hydroxylase
(decarboxylating), from Candida parapsilosis CBS604 was purified to
apparent homogeneity. The enzyme is induced when the yeast is grown on
either 4-hydroxybenzoate, 2,4-dihydroxybenzoate, or 3,4- dihydroxybenzoate
as the sole carbon source. The purified monooxygenase is a monomer of about
50 kDa containing flavin adenine dinucleotide as weakly bound cofactor.
4-Hydroxybenzoate 1-hydroxylase from C. parapsilosis catalyzes the
oxidative decarboxylation of a wide range of 4-hydroxybenzoate derivatives
with the stoichiometric consumption of NAD(P)H and oxygen. Optimal
catalysis is reached at pH 8, with NADH being the preferred electron donor.
By using (18)O2, it was confirmed that the oxygen atom inserted into the
product 1,4-dihydroxybenzene is derived from molecular oxygen. 19F nuclear
magnetic resonance spectroscopy revealed that the enzyme catalyzes the
conversion of fluorinated 4-hydroxybenzoates to the corresponding
hydroquinones. The activity of the enzyme is strongly inhibited by
3,5-dichloro-4- hydroxybenzoate, 4-hydroxy-3,5-dinitrobenzoate, and 4-
hydroxyisophthalate, which are competitors with the aromatic substrate. The
same type of inhibition is exhibited by chloride ions. Molecular orbital
calculations show that upon deprotonation of the 4-hydroxy group,
nucleophilic reactivity is located in all substrates at the C-1 position.
This, and the fact that the enzyme is highly active with
tetrafluoro-4-hydroxybenzoate and 4-hydroxy-3-nitrobenzoate, suggests that
the phenolate forms of the substrates play an important role in catalysis.
Based on the substrate specificity, a mechanism is proposed for the
flavin-mediated oxidative decarboxylation of 4-hydroxybenzoate.
Copyright © 1997, American Society for Microbiology
Purification and properties of 4-hydroxybenzoate 1-hydroxylase (decarboxylating), a novel flavin adenine dinucleotide-dependent monooxygenase from Candida parapsilosis CBS604
Department of Biochemistry, Wageningen Agricultural University, The Netherlands.
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