Study of the substrate specificities of the extracellular lignin peroxidases of the wood-destroying fungusPleurotus ostreatus

Abstract

The substrate specificities of two forms of purified extracellular lignin peroxidase isolated from a total enzyme preparation of the fungus Pleurotus ostreatus — LGP-1 and LGP-II — have been determined. The substrate specificities of the isoenzymes differ considerably: LGP-I preferentially destroys model compounds of lignin — the β-guaiacyl ether of I-veratrylpropanol, coniferyl alcohol, and pyrocatechol, while LGP-II is most specific in relation to veratryl alcohol, veratrylpropane-1,3-diol, and vanillyl alcohol. Both forms partially oxidize syringaldazine and ABTS. The isoenzymes possess peroxidase and oxidase properties simultaneously, since veratryl, vanillyl, and coniferyl alcohols were oxidized by both forms of the enzyme only in the presence of H2O2, which confirms their peroxidase natures. At the same time, ABTS, syringaldazine, pyrocatechol, and o -phenylenediamine were also oxidized by the lignin peroxidase in the absence of H2O2, which confirms their oxidase function. The isoenzymes also possess Mn-peroxidase activity in relation to NADH. Since almost all substrates were oxidized by the enzymes only in the presence of hydrogen peroxide, they cannot be assigned to the class of oxidases. On the other hand, the LGP ofP. ostreatus is not Mn-dependent, since the presence of manganese ions had no effect whatever on the oxidation of aromatic substrates by the enzyme. Moreover, both forms of the enzyme oxidized veratryl alcohol — a specific substrate for ligninases, which permits the extracellular isoenzymes of P. ostreatus, LGP-I and LGP-II, to be assigned to the class of ligninases.