Oxidation and nitration of mononitrophenols by a DyP-type peroxidase.

Substantial conversion of nitrophenols, typical high-redox potential phenolic substrates, by heme peroxidases has only been reported for lignin peroxidase (LiP) so far. But also a dye-decolorizing peroxidase of Auricularia auricula-judae ( Aau DyP) was found to be capable of acting on (i) ortho -nitrophenol ( o NP), (ii) meta -nitrophenol ( m NP) and (iii) para -nitrophenol ( p NP). The pH dependency for p NP oxidation showed an optimum at pH 4.5, which is typical for phenol conversion by DyPs and other heme peroxidases. In the case of o NP and p NP conversion, dinitrophenols (2,4-DNP and 2,6-DNP) were identified as products and for p NP additionally p -benzoquinone. Moreover, indications were found for the formation of random polymerization products originating from initially formed phenoxy radical intermediates. Nitration was examined using 15 N-labeled p NP and Na 14 NO 2 as an additional source of nitro-groups. Products were identified by HPLC–MS, and mass-to-charge ratios were evaluated to clarify the origin of nitro-groups. The additional nitrogen in DNPs formed during enzymatic conversion was found to originate both from 15 N- p NP and 14 NO 2 Na. Based on these results, a hypothetical reaction scheme and a catalytically responsible confine of the enzyme’s active site are postulated. [ABSTRACT FROM AUTHOR]