A pH-stable Yellow Laccase from White Rot Fungus Trametes sp. SQ01: Rapid Purification and Characterization

Abstract:

The white rot fungus Trametes sp. SQ01 secretes a high level of laccase in the basal liquid medium without induction. The laccase has been purified to homogeneity through acetate acetone precipitation and DEAE-cellulose 52 anion-exchange chromatography with a final purification fold of 15.4 and an overall yield of 43.6%. The purified enzyme was identified with a molecular mass of 62 kD by SDS gel electrophoresis. The purified enzyme was not blue like the typical laccase but yellow, and had not the basic spectroscopic features of a typical blue laccase. The enzyme oxidized a series of diphenol, creosol and non-phenol, including 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulfonate) (ABTS), catechols, hydropuinone, 2,6-dimethoxyphenol (DMP), and guaiacol. With ABTS as a substrate, the optimum pH and temperature for the purified laccase were 4.5 and 70°C, respectively. The enzyme was highly stable in the pH range 3~11, and the most stable under the pH 5.0. The enzyme was stable up to 50°C, and had half-life of 30 min at 60°C. The susceptibility of laccase towards several surfactants, inhibitors and metal cations was also assessed. The enzyme activity was completely inhibited by DTT at the concentration of 1 mmol/L, but 1 mmol/L of SDS activated the laccase activity by 128%. Laccase activity was also inhibited by several metal cations at a 5 mmol/L of concentration, especially Mn2+. The purified enzyme efficiently decolorized Remazol Brilliant Blue R (RBBR) in the absence of added redox mediators. The high production of Trametes. sp. SQ01 laccase as well as its decolorization ability demonstrated its potential application on dye decolorization.

Key words:Laccase, Purification, pH stability, Substrate specificity, Dye decolorization