A NOVEL WHITE LACCASE FROM PLEUROTUS-OSTREATUS

Two laccase isoenzymes (POXA1 and POXA2) produced by Pleurotus ostreat us were purified and fully characterized, POXA1 and POXA2 are monomeri c glycoproteins with 3 and 9% carbohydrate content, molecular masses o f about 61 and 67 kDa by sodium dodecyl sulfate polyacrylamide gel ele ctrophoresis, of about 54 and 59 kDa by gel filtration in native condi tions, and of 61 kDa by matrix-assisted laser desorption ionization ma ss spectrometry (only for POXA1) and pI values of 6.7 and 4.0, respect ively, The N terminus and three tryptic peptides of POXA1 have been se quenced, revealing clear homology with laccases from other microorgani sms, whereas POXA2 showed a blocked N terminus, The stability of POXA2 as a function of temperature was particularly low, whereas POXA1 show ed remarkable high stability with respect to both pH and temperature. Both enzymes oxidize syringaldazine and ABTS (2, 2'-azino-bis(3-ethylb enzothiazoline-6-sulfonic acid)) together with a variety of different substituted phenols and aromatic amines with the concomitant reduction of oxygen, but POXA1 is unable to oxidize guaiacol, Both enzymes were strongly inhibited by sodium azide and thioglycolic acid but not by E DTA. UV/visible absorption spectra, atomic adsorption, and polarograph ic data indicated the presence of 4 copper atoms/mol of POXA2 but only one copper, two zinc, and one iron atoms were found/mol of POXA1. The neutral pI and the anomalous metal content of POXA1 laccase render th is enzyme unique in its structural characteristics. The lack of typica l absorbance at 600 nm allows its classification as a ''white'' laccas e.