DEGRADATION OF HUMIC ACIDS BY MANGANESE PEROXIDASE FROM THE WHITE-ROTFUNGUS CLITOCYBULA-DUSENII

The depolymerization of humic acids (HAs) obtained from low-rank coal (lignite) to fulvic acids (FAs) was investigated in a cell-free system (in vitro) using manganese peroxidase (MnP) from the white-rot fungus Clirocybula dusenii b11. MnP was produced in surface cultures of C. d usenii which were induced with manganese(II) ions (Mn2+, 300 mu M) The optimum conditions for the action of MnP were determined by varying f ollowing parameters of the enzyme assay: i) concentration of Mn2+, ii) concentration of hydrogen peroxide (H2O2), iii) pH value and iv) temp erature. Optimum parameters determined were used in subsequent in vitr o depolymerization studies of humic acids. For that purpose, following parameters of the reaction mixture were additionally varied: concentr ation of HAs, concentration of the thiol mediator glutathione (GSH), p resence and concentration of organic solvents. As the result, followin g parameters were found to be optimal for the MnP-catalyzed in ville d epolymerization of HAs into low-molecular weight FAs (MnP activity 0.1 2 U/ml): 250 mu g/ml HAs, 1 mM MnCl2, 46 mu M/min H2O2 (continuously s upplied by glucose oxidase), 600 mu M GSH, 4% (v/v) N,N-dimethylformam ide (DMF), pH 4.0, and 37 degrees C.