An alkali-stable enzyme with laccase activity from entophytic fungus and the enzymatic modification of alkali lignin

Mycelia Sterilia YY-5, an entophytic fungus, was isolated from Rhus chinensis Mill and its extracellular enzyme had a higher laccase activity (MS-Lac). After been purified by anion exchange and gel filtration chromatography, MS-Lac, which had a molecular mass of 45 kDa, was found to be an alkali-stable enzyme with an optimum pH of 10.0 and capable of retaining 80% activity after incubation for 72 h with syringaldazine as substrate. It was also found that syringaldazine had a higher affinity than 2,2′-azino-bis-(3-ethylbenzothiazoline)-6-sulphonate (ABTS) as substrate for MS-Lac, which was determined in sodium phosphate buffer (pH 6.0, 0.1 M) at 30 °C. Meanwhile, the lignin modification, catalyzed by MS-Lac, indicated that it could oxidize the phenolic hydroxyl, side chain substituent or carbonyl group of spruce alkali lignin in cetyltrimethylammonium bromide (CTAB) reversed micelles (20 mM, pH 6.0, W/O = 40) and steam-exploded wheat straw alkali lignin in NaOH solution (20 mM, pH 10.0).