Laccase component of the Ceriporiopsis subvermispora lignin-degrading system

Laccase activity in the lignin-degrading fungus Ceriporiopsis subvermispora was associated with several proteins in the broth of cultures grown in a defined medium. Activity was not increased significantly by adding 2,5-xylidine or supplemental copper to the medium. Higher activity, associated with two major isoenzymes, developed in cultures grown on a wheat bran medium. These two isoenzymes were purified to homogeneity. L1 and L2 had isoelectric points of 3.4 and 4.8, molecular masses of 71 and 68 kDa, and approximate carbohydrate contents of 15 and 10%, respectively. Data indicated 4 copper atoms per mol. L1 and L2 had overlapping pH optima in the range of 3 to 5, depending on the substrate, and exhibited half-lives of 120 and 50 min at 60 degrees C. They were strongly inhibited by sodium azide and thioglycolic acid but not by hydroxylamine or EDTA. The isoenzymes oxidized 1,2,4,5-tetramethoxybenzene but not other methoxybenzene congeners. A variety of usual laccase substrates, including lignin-related phenols and ABTS [2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid)], were also oxidized. Kinetic parameters were similar to those of the laccases of Coriolus versicolor. The N-terminal amino acid sequence (20 residues for L1) showed significant homology to those of laccases of other white rot basidiomycetes but not to those of the laccases of Agaricus bisporus or Neurospora crassa.