Biochemical characterization and kinetic studies on a purified yellow laccase from newly isolated Aureobasidium pullulans NAC8 obtained from soil containing decayed plant matter

The study investigated the biochemical characteristics and kinetic parameters of laccase from a newly isolated Aureobasidium pullulans NAC8 obtained from soil containing decay plant litters. This was with a view to identifying the type of laccase and its possible suitability for biotechnological applications. The fungal strain was identified as A. pullulans NAC8 by sequencing of its 5.8S rRNA and adjacent internally transcribed sequences (ITS) 1 and 2. A. pullulans NAC8 laccase was purified 2.0-fold with a yield of 59.3% and specific activity of 9.34 μmol/min/mg protein. The kinetic parameters K(M), V(max), k(cat) and k(cat)/K(M) for laccase with guaiacol as substrate were 1.05 ± 0.12 mM, 12.67 ± 0.55 μmol/ml/min, 25.3 × 10(−1) s(−1) and 2.4 × 10(3) M(−1) s(−1) respectively. Laccase exhibited maximum activity at 45 °C and optimum pH of 4.5. The enzyme showed stability at a temperature range of 45–55 °C after a 2 h incubation. The molecular weight determined on SDS–PAGE was 68.4 kDa. The enzyme was stable at 10% of all organic solvents used but displayed a loss of activity at 50%. 2.5 mM thioglycolic acid (TGA) and 0.05 mM sodium azide inactivated the enzyme. The substrate specificity was guaiacol > catechol > tannic acid > gallic acid. There was no peak observed at 610 nm and the ratio of absorbance at 280 nm and 610 was 26. This suggests a yellow laccase. The biochemical properties of A. pullulans NAC8 yellow laccase makes it potentially useful in several biotechnological applications.