Mineralization and solubilization of synthetic lignin by manganese peroxidases from Nematoloma frowardii and Phlebia radiata

Crude and purified manganese peroxidase from the white-rot fungi Nematoloma frowardii and Phlebia radiata catalyzed the partial depolymerization of a [C-14-ring]labelled synthetic lignin into water-soluble fragments (30-50%). The in vitro depolymerization of the C-14-labelled lignin was accompanied by a release of (CO2)-C-14 ranging from 4 to 6%. Small quantities of the th iol mediator glutathione stimulated the depolymerization of lignin resultin g in a mineralization and solubilization of up to 10 and 64%, respectively. Most of the water-soluble substances formed had molecular masses around 0. 7 kDa, although a higher-molecular mass fraction was also detectable (>2 kD a). Photometric assays using 2,2'-azinobis(3-ethylbenzothiazolinesulphonate ) as an indicator demonstrated that high levels of Mn(IIE), which were very probably responsible for the depolymerization and mineralization of the C- 14-labelled lignin, were adjusted within the first 24 h of incubation. The manganese peroxidase catalyzed depolymerization process was not necessarily dependent on H2O2; also in the absence of the H2O2-generating system gluco se/glucose oxidase, effective solubilization and mineralization of lignin d ehydrogenation polymerizate occurred, due to the in part superoxide dismuta se sensitive, 'oxidase-like' activity of MnP which probably produces radica l species and peroxides from malonate. (C) 1999 Elsevier Science B.V. All r ights reserved.