Isolation and purification of laccase from rice straw fermented with Pleurotus sajor-caju

Rice crop is abundant in Malaysia. With the high demand of food sources, the amount of rice straw left in the plantation field increases over time. This highly lignocellulosic material is a promising substrate to produce laccase- a versatile enzyme of low specificity that can function well in several important areas such as bioremediation, industry, agriculture and medicine. Utilizing the rice straw in a solid-state fermentation process using Pleurotus sajor-caju, laccase was produced and subjected to isolation and purification processes. The optimum laccase production was studied from 0 to 21 days. The highest laccase activity of 224.93 U/mg was obtained from the crude extract after 9 days of fermentation with Pleurotus sajor-caju. It was concentrated by ultrafiltration and purified using DEAE-Sepharose anion exchange chromatography. The peak fraction obtained was then loaded into Sephacryl S200-HR gel filtration chromatography. Laccase was purified by 43-fold to a specific activity of 19335 U/mg, with an overall protein recovery of 18.6%. It appeared as a single band on SDS-PAGE with an apparent molecular weight of 53 kDa.