Substrate-modulated reactions of putidamonooxin. The nature of the active oxygen species formed and its reaction mechanism.
1. 4-Methoxybenzoate monooxygenase is fairly nonspecific. The enzyme system with putidamonooxin as its oxygen-activating component catalyses: (a) O-, S- and N-demethylation; (b) the oxygenation of 4-methylbenzoate and 4-methylmercaptobenzoate, with formation of 4-carboxybenzyl alcohol and 4-carboxyphenylmethyl sulfoxide, respectively, and (c) attack of the aromatic ring of 4- and 3-hydroxybenzoate and 4-aminobenzoate, yielding 3,4-dihydroxybenzoate and 4-amino-3-hydroxybenzoate, respectively. 2. Compounds which are bound by the active sites of putidamonooxin have two essential features in common: a planar aromatic ring system, and a free carboxyl group attached to it. 3. By a substrate-modulated reaction putidamonooxin can be induced to function not only as a monooxygenase but also as a peroxotransferase, i.e. it incorporates both atoms of the activated oxygen molecule into a substrate molecule. This finding supports the hypothesis that a mesomeric state of the iron.peroxo complex, [FeO2]+, is indeed the active oxygenating species of putidamonooxin. 4. The lifetime of the ternary complex consisting of enzyme.iron-peroxo-complex.substrate is significantly prolonged by uncoupling and partially uncoupling substrates, except when it is inactivated by protonation of the iron.peroxo complex by a proton transported into the active sites by a special kind of substrate (i.e. isomers of monoaminobenzoate), with the direct formation of H2O2. 5. The lifetime of the active oxygen species is determined by (a) the rate of the oxygenation reaction in the presence of tight-coupling substrates and (b) the rate of the oxygenation reaction as well as detoxification by the availability of a dissociable proton in the presence of partial uncoupling (and uncoupling) substrate analogues. 6. The rate of the oxygenation reaction depends on the lifetime of the active oxygen species, [FeO2]+, in the presence of partial uncoupling substrates. 7. The iron.peroxo complex attacks an aromatic ring system according to the empiric rules of electrophilic substitution, whereas the attack of aliphatic substituents at the aromatic ring is controlled by steric criteria.
Wende
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P
Fachrichtung Physiologische Chemie der Universität des Saarlandes, Homburg, Federal Republic of Germany.
Bernhardt
F H
FH
Pfleger
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K
D001565:Benzoates / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D007700:Kinetics; D013058:Mass Spectrometry; D008667:Metalloproteins / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D010103:Oxygen Isotopes; D010105:Oxygenases / Q000378:metabolism*; D013379:Substrate Specificity
D001565:Benzoates; D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D009097:Multienzyme Complexes; D010103:Oxygen Isotopes; D010105:Oxygenases; C022485:putidamonooxin; D010100:Oxygen