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Despite numerous reports concerning the biodegradation of rubber materials, there has been no report of rubber degradation by fully characterized enzymes. In the present paper, we presented a new method to decompose nonvulcanized and vulcanized polyisoprene rubbers by controlling the free radical chain reactions of lipids using oxidative enzymes, manganese peroxidase (MnP), laccase (Lac), and horseradish peroxidase (HRP). Nonvulcanized synthetic polyisoprene (IR) was degraded by the free radicals from unsaturated fatty acids produced by MnP, HRP, and a combination of Lac/1-hydroxybenzotriazole. In contrast, lipoxygenase caused no apparent degradation. Degradation of IR was also observed in lipid peroxidation initiated by the Fenton reaction (FR) and Mn(III), an oxidation product produced by MnP. Vulcanized polyisoprene rubber sheets were degraded by the lipid peroxidation initiated by HRP, MnP, Mn(III), and FR. Pyrolysis GC-MS analysis demonstrated that the lipid peroxidation liberated isoprenoid fragments from the vulcanized rubbers.

Glyoxal is a key compound involved in glyoxal oxidase (GLOX)-dependent production of glyoxylate, oxalate and H2O2 by lignin-degrading basidiomycetes. In this paper, we report that glyoxal was produced from a metabolite of ligninolytic fungi, linoleic acid, by manganese peroxidase (MnP)-dependent lipid peroxidation. In the absence of the parent substrate of linoleic acid, the dialdehyde was oxidized by MnP and Mn(III) chelate to start free radical reactions with emission of chemiluminescence at 700–710 nm. The spectroscopic profile of the light emission is distinguishable from (a) singlet oxygen, (b) triplet carbonyls from dioxetane and α-hydroxyperoxyl radicals, and (c) biacyl triplet formed by the coupling of two acyl radicals. The photon emission of glyoxal by MnP was activated by co-oxidation of tartrate. The MnP-dependent oxidation of glyoxal in tartrate buffers continued for 10 days without addition of exogenous H2O2. The importance of these results is discussed in relation to the free radical chemistry of lignin biodegradation by wood rot fungi. [ABSTRACT FROM AUTHOR]

Lipid peroxidation by managanese peroxidase (MnP) is reported to decompose recalcitrant polycyclic aromatic hydrocabon (PAH) and nonphenolic lignin models. To elucidate the oxidative process, linoleic acid and 13(S)-hydroperoxy-9Z,11E-octadecadienoic acid [13(S)-HPODE] were reacted with MnPs from Ceriporiopsis subvermispora and Bjerkandera adusta and the free radicals produced were analyzed by ESR. When the MnPs were reacted with 13(S)-HPODE in the presence of Mn(II), H2O2 and tert-nitrosobutane (t-NB), the ESR spectrum contained a sharp triplet of acyl radical (aN = 0.81 mT). Formation of acyl radical was also observed in the reactions of Mn(III)-tartrate with 13(S)-HPODE and with linoleic acid, but the latter reaction occurred explosively after an induction period of around 30 min. Reactions of MnP with linoleic acid in the presence of Mn(II), H2O2 and t-NB gave no spin adducts while addition of t-NB after preincubation of linoleic acid with MnP/Mn(II)/H2O2 for 2 h gave spin adducts of carbon-centered (aN = 1.53 mT, aH = 0.21 mT) and acyl (aN = 0.81 mT) radicals. In contrast to linoleic acid, methyl linoleate and oleic acid were not peroxidized by MnP and chelated Mn(III) within a few hours, indicating that structures containing both the 1,4-pentadienyl moiety and a free carboxyl group are necessary for inducing the peroxidation in a short reaction time. These results indicate that MnP-dependent lipid peroxidation is not initiated by direct abstraction of hydrogen from the bis-allylic position during turnover but proceeds by a Mn(III)-dependent hydrogen abstraction from enols and subsequent propagation reactions involving the formation of acyl radical from lipid hydroperoxide. This finding expands the role of chelated Mn(III) from a phenol oxidant to a strong generator of free radicals from lipids and lipid hydroperoxides in lignin biodegradation. [ABSTRACT FROM AUTHOR]

A cellulolytic active oxygen species, hydroxyl radicals (⋅OH), play a leading role in the erosion of wood cell walls by brown-rot and non-selective white-rot fungi. In contrast, selective white-rot fungi have been considered to possess unknown systems for the suppression of ⋅OH production due to their wood decay pattern with a minimum loss of cellulose. In the present paper, we first report that 1-nonadecene-2,3-dicarboxylic acid, an alkylitaconic acid (ceriporic acid B) produced by the selective white-rot fungus Ceriporiopsis subvermispora intensively inhibited ⋅OH production by the Fenton reaction by direct interaction with Fe ions, while non-substituted itaconic acid promoted the Fenton reaction. Suppression of the Fenton reaction by the alkylitaconic acid was observed even in the presence of the Fe3+ reductants, cysteine and hydroquinone. The inhibition of ⋅OH production by the diffusible fungal metabolite accounts for the extracellular system of the fungus that attenuates the formation of ⋅OH in the presence of iron, molecular oxygen, and free radicals produced during lignin biodegradation. [Copyright &y& Elsevier]