Dioxygen Activation by Putidamonooxin

• Published in: European journal of biochemistry Vol. 120; no. 3; pp. 547 - 555
• Main Authors: BERNHARDT, Frithjof‐Hans, KUTHAN, Hartmut
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.12.1981
• ISSN: 0014-2956; 1432-1033
• DOI: 10.1111/j.1432-1033.1981.tb05735.x

In the presence of substrates not favourable for hydroxylation, more than 80% of the dioxygen consumed by purified, reconstituted 4‐methoxybenzoate monooxygenase appears in the reaction mixture as hydrogen peroxide. We have investigated whether under these conditions (a) reduced putidamonooxin, the oxygenase of this enzyme system, either autoxidizes in the presence of dioxygen, with liberation of superoxide anion radicals which then disproportionate to H2O2 and O2, or (b) dioxygen is reduced by two sequential single‐electron steps leading to the active oxygen species that forms hydrogen peroxide directly when inactivated by protonation. Quantitative estimation of O−2 radicals, with either succinylated ferricytochrome c or epinephrine used as O−2 scavengers, revealed that only about 6% of the total electron flux channeled via putidamonooxin to dioxygen led to the monovalent reduction of dioxygen. This means that not more than 3% of the hydrogen peroxide found under uncoupling conditions arises from the rapid bimolecular disproportionation of initially formed O−2 radicals. Inconsistent results were obtained when lactoperoxidase was used as an O−2 trap. Our measurements indicate that the conversion of lactoperoxidase into compound III is an inappropriate method of detecting any O−2 radicals that may be formed by the uncouplex 4‐methoxybenzoate monooxygenase. The stoichiometry of about 1:1 for O2 uptake: H2O2 formation indicates that under uncoupling conditions H2O is virtually not formed. The role of [FeO2]+ as the active oxygenating species of putidamonooxin is discussed.