Fungal laccase: properties and activity on lignin.

The sources of ligninocellulose that occur in various forms in nature are so vast that they can only be compared to those of water. The results of several, more recent experiments showed that laccase probably possesses the big ability for "lignin-barrier" breakdown of ligninocellulose. The degradation of this compound is currently understood as an enzymatic process mediated by small molecules, therefore, this review will focus on the role of these mediators and radicals working in concert with enzymes. The fungi having a versatile machinery of enzymes are able to attack directly the "lignin-barrier" or can use a multienzyme system including "feed-back" type enzymes allowing for simultaneous transformation of lignin and carbohydrate compounds.

Biodegradation of lignin by white rot fungi.

A review is presented related to the biochemistry of lignocellulose transformation. The biodegradation of wood constituents is currently understood as a multienzymatic process with the mediation of small molecules; therefore, this review will focus on the roles of these small molecular compounds and radicals working in concert with enzymes. Wood rotting basidiomycetous fungi penetrate wood and lead to more easily metabolized, carbohydrate constituents of the complex. Having a versatile machinery of enzymes, the white rot fungi are able to attack directly the "lignin barrier." They also use a multienzyme system including so-called "feed back" type enzymes, allowing for simultaneous transformation of both lignin and cellulose. These enzymes may function separately or cooperatively.

Dearomatization of lignin derivatives by fungal protocatechuate 3,4-dioxygenase immobilized on porosity glass.

Protocatechuate 3,4-dioxygenase (see protocatechuate: oxygen 3,4-oxidoreductase, EC 1.13.11.3) was isolated from the mycelium of Pleurotus ostreatus (induced with p-hydroxybenzoic acid) and immobilized on controlled porosity glass beads. Four fractions of Na-lignosulfonates (varying in M(r), after chromatography on Sephadex G-50) were treated with the immobilized enzyme. The products after incubation showed the same M(r) as the untreated fractions, but their light absorption at 280 nm considerably decreased. These studies indicate that dioxygenase causes partial dearomatization of lignin macromolecule.

Aromatic ring cleavage of protocatechuic acid by the white-rot fungus Pleurotus ostreatus.

In Pleurotus ostreatus protocatechuic acid is degraded by protocatechuate 3,4-dioxygenase (protocatechuate: oxygen 3,4-oxidoreductase, EC 1.13.11.3) via "intradiol" cleavage of aromatic ring to form beta-carboxy-cis,cis-muconic acid. The enzyme was isolated from the mycelium induced with p-hydroxybenzoic acid. An about 460-fold purification of the enzyme was achieved by ammonium sulphate fractionation, and DEAE-cellulose and Sephadex G-200 chromatography. The enzyme was homogeneous on analytical electrophoresis under non-denaturing conditions, whereas in the presence of sodium dodecyl sulphate several polypeptides of low molecular weight appeared additionally in trace amounts. Molecular weight of the enzyme, determined by gel filtration and electrophoresis was 200 000 and 205 000, respectively. The enzyme showed low substrate specificity, its pH optimum was 8.0 and Michaelis constant for protocatechuic acid was 14.2 microM.

Biotransformation of sodium lignosulfonates of different molecular weights by the fungus Pleurotus ostreatus.

Fractions of sodium lignosulfonates (NaLS) of varied molecular weight, obtained by gel-permeation chromatography on Sephadex G-50, were exposed to microbiological degradation using liquid cultures of Pleurotus ostreatus. The intensity of transformation observed during 4 weeks of growth (based on nitroso determinations) was inversely proportional to the molecular weight of the fractions studied. Degradation of lignosulfonates was accompanied by polymerization, particularly where low molecular weight fractions were involved. The activity of p-diphenol oxidase (laccase) was stimulated by the presence of lignosulfonates. This effect was especially noticeable in the case of high molecular weight components.