A Novel White Laccase from Pleurotus ostreatus

Abstract

Two laccase isoenzymes (POXA1 and POXA2) produced by Pleurotus ostreatus were purified and fully characterized. POXA1 and POXA2 are monomeric glycoproteins with 3 and 9% carbohydrate content, molecular masses of about 61 and 67 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis, of about 54 and 59 kDa by gel filtration in native conditions, and of 61 kDa by matrix-assisted laser desorption ionization mass spectrometry (only for POXA1) and pI values of 6.7 and 4.0, respectively. The N terminus and three tryptic peptides of POXA1 have been sequenced, revealing clear homology with laccases from other microorganisms, whereas POXA2 showed a blocked N terminus. The stability of POXA2 as a function of temperature was particularly low, whereas POXA1 showed remarkable high stability with respect to both pH and temperature.Both enzymes oxidize syringaldazine and ABTS (2, 2-azino-bis(3-ethylbenzothiazoline-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 EDTA.UV/visible absorption spectra, atomic adsorption, and polarographic 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 this enzyme unique in its structural characteristics. The lack of typical absorbance at 600 nm allows its classification as a "white" laccase.

Extracellular Laccase Produced by an Edible Basidiomycetous Mushroom,Grifola frondosa: Purification and Characterization

“…Absorption spectrum of Lac 1 As shown in Fig. 2, the absorption spectrum of Lac 1 had typical characteristics of copper containing enzymes, 38,39) having an absorption peak at 610 nm and a shoulder at around 350 nm. This indicates that Lac 1 contains a type-1 copper atom, which is responsible for the blue color of the concentrated enzyme (shown by the absorption peak at 610 nm) and type-3 binuclear copper atoms (shown by the absorption shoulder at 350 nm).…”

Optimization of Biological Pretreatment of Green Table Olive Processing Wastewaters Using Aspergillus niger

“…One unit of LiP activity was defined as the amount of enzymes catalyzing the formation of 1µmol of veratraldehyde per minute under the assay conditions. Laccase activity was determined by monitoring the oxidation of 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) at 420nm following the method of Palmieri et al [26]. The reaction mixtures (1 ml) were prepared using 20 µl of culture broth, 880 µl of citratephosphate buffer (pH 3.0) and 100 µl 1 mM ABTS, and the temperature was adjusted to 30°C.…”

Assessing the tolerance of immobilized laccase from a salt-tolerant strain of Trichoderma viride Pers NFCCI-2745 to heavy metal ions, detergents and copper chelating agents

“…No beads were formed for MgSO 4 and HgCl 2 , when used as cross-linkers either alone or in combination with CuSO 4 . Laccase is a copper-dependent enzyme, and thus, Cu ions play an important role in maintaining the catalytic mechanism of laccase (Palmieri et al 1997;Duran et al 2002). It was earlier reported that Cu-alginate laccase from Trametes villosa gave better immobilization yield than Ca-alginate for laccase (Brandi et al 2006).…”