Cooxidation of styrene by horseradish peroxidase and phenols: a biochemical model for protein-mediated cooxidation

Abstract

Styrene is oxidized to styrene oxide and benzaldehyde when incubated with horseradish peroxidase, H2O2, and 4-methylphenol. Styrene oxide is not formed in the absence of any of these reaction components or of molecular oxygen. The coupling products 2-(4-methylphenoxy)-1-phenylethane, 2-(4-methylphenoxy)-1-phenylethan-1-ol, and 2-(4-methylphenoxy)-2-phenylethan-1-ol are not formed, but the ortho-linked dimer of 4-methylphenol is a major product. The epoxide oxygen is labeled in the presence of 18O2 but not H218O2. Styrene oxide formation is not inhibited by mannitol or superoxide dismutase. The stereochemistry of trans-[1-2H]styrene is partially scrambled in the epoxide product. EPR signals attributable to the 2,4-dihydroxy-5-methylphenoxy radical, a product of the oxidation of 4-methylcatechol, are observed if Zn2+ is added to stabilize the radical. This radical is only detected in the presence of styrene. The results imply that styrene is epoxidized by the hydroperoxy radical generated by addition of molecular oxygen to the 4-methylphenoxy radical. The epoxidation mimics the chemistry proposed to occur in the protein-mediated cooxidation of styrene by hemoglobin and myoglobin.

Enantioselective Epoxidation and Carbon–Carbon Bond Cleavage Catalyzed by Coprinus cinereus Peroxidase and Myeloperoxidase

“…The fact that MPO is about 10 times as active as CiP in the epoxidation of styrene can probably be accounted for by the higher reactivity or higher redox potential of compound I, which for MPO has a very short lifetime (40). The formation of benzaldehyde as a side product in the epoxidation of alkenes, which is observed for both CiP and MPO (Table II), has been described before only for HRP in the cooxidation of styrene with 4-methylphenol (27) and in the direct epoxidation of styrene by some HRP mutants (22,25,26). Noteworthy, it was specifically stated that both CPO-catalyzed (11) and cytochrome c peroxidase-catalyzed (20) oxidations of styrene did not lead to benzaldehyde formation.…”

“…Moreover, we show that both CiP and MPO are also capable of catalyzing C-␣-C-␤ bond cleavage of (electron-poor) styrene derivatives without the necessity for the presence of a phenol as a co-substrate, as is the case in the cooxidation of styrene by HRP and phenols (27). So far, the only heme peroxidase known to catalyze C-C bond cleavage of nonphenolics has been lignin peroxidase (42,43 (45).…”

“…By site-directed mutagenesis, it was possible to convert horseradish peroxidase (HRP), which in the wild type form only generates trace amounts of epoxide, into a species having good peroxygenase activity (22)(23)(24)(25)(26). However, native HRP will oxidize styrene in the presence of H 2 O 2 to form styrene oxide and benzaldehyde only when 4-methylphenol is present via a cooxidation mechanism (27). MPO has previously been shown to perform the epoxidation of butadiene (28), but so far enantioselective epoxidations by this enzyme have not been reported.…”

Plasmodium falciparum Histidine-rich Protein-2 (PfHRP2) Modulates the Redox Activity of Ferri-protoporphyrin IX (FePPIX)

“…The latter pathway is associated with the formation of alkoxyl radicals (Scheme 1) that can co-oxidize suitable substrates (23,24). We therefore incubated PLPC with 18:2-OOH and FePPIX in the absence and presence of PfHRP2.…”

Interfaces com a indústria

“…A inspiração para este trabalho veio de uma publicação de de Montellano 49 onde, pelo uso de um iniciador, a peroxidase de raiz forte catalisava a epoxidação enantiosseletiva de estireno. Entretanto, como o custo desta enzima inviabilizava seu uso, por um lado e por outro nos limitaria a uma faixa estrita de substratos, passamos a investigar o possível uso de peroxidases presentes em vegetais abundantes de baixo custo, como nabo e rabanete.…”