Free radical process controlled by lipid-related metabolites produced by the biopulping fungus, ceriporiopsis subvermispora

摘要

The best biopulping fungus, Ceriporiopsis subvermispora degrades lignin at a site far from enzymes. As a possible ligninolytic system by this fungus we proposed a mechanism involving in situ lipid peroxidation catalyzed by metal complexes. In an incipient stage of wood decay by C. subvermispora, the fungus produced manganese peroxidase (MnP) and free fatty acids including linoleic acid. In prolonged cultivation period after two weeks, the fatty acids were consumed with concomitant production of organic hydroperoxides and TBARS. MnP is an enzyme that oxidizes Mn (II) to Mn (III), which in turn oxidizes phenolic compounds if suitable chelators for the manganese ions are present. By in vitro experiments, we found that the diffusible Mn (III) chelate initiated peroxidation of linoleic acid to generate acyl radicals and glyoxal. The marker compound for the Mn (III)-dependent lipid peroxidation, glyoxal was also found as a major aldehyde in the wood meal cultures of this fungus. In the analysis of lipid peroxidation by C. subvermispora, we also found that this fungus produced novel alkylitaconates (ceriporic acids). We synthesized one of the major alkylitaconates, 1-nonadecene-2, 3-dicarboxylic acid (ceriporic acid B) by Grignard reaction. Using the chemically synthesized ceriporic acid B, we found that iron redox reactions were strongly suppressed by the alkylitaconate to inhibit production of a cellulolytic active oxygen species, hydroxyl radicals. Thus, lignolysis by the selective white rot fungus is not explained by the direct interaction between oxidative enzymes and the lignin. Analysis of the lignin-degrading reactions controlled by the fungal metabolites will give us a new insight into the development of environmentally friendly processes for pulp and paper production.