Purification and characterization of two lignin peroxidase isozymes produced by Bjerkandera sp. strain BOS55

Abstract

The white-rot fungus Bjerkandera sp. strain BOS55 excretes at least seven lignin peroxidase (LiP) isozymes. Two of these, LiP-2 and LiP-5 (molecular weight 40–42 kDa), were purified to homogeneity. Both isozymes had the same N-terminal amino acid sequence which showed strong homology with LiP isozymes produced by other white-rot fungi. The kinetics of both isozymes were similar. LiP-5 oxidized veratryl alcohol optimally only in the presence of H 2O 2 near pH 3.0 (16.7 U/mg) and LiP-2 did this below pH 2.5 (33.8 U/mg). Also at normal physiological pHs for fungal growth (pH 5.0–6.5) both isozymes were still active. Further characterization of LiP-2 and LiP-5 revealed that the K m for H 2O 2 strongly decreased with increasing pH. As a result of this the catalytic efficiency (TN/ K m) calculated on the basis of the K m for H 2O 2 in the oxidation of veratryl alcohol was constant over wide pH range.