Purification and characterization of yellow laccase from Trametes hirsuta MTCC-1171 and its application in synthesis of aromatic aldehydes

• Purification and characterization of yellow laccase from new fungal strain.
• Use of this purified laccase in syntheses of several aromatic aldehydes.
• No mediator used for such syntheses.
• Identification of products by HPLC and IR.

A yellow laccase from the culture filtrate of Trametes hirsuta MTCC-1171 has been purified. The purification methods involved concentration of the culture filtrate by ammonium sulphate precipitation and an anion exchange chromatography on diethylaminoethyl cellulose. The sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and native polyacrylamide gel electrophoresis gave single protein band indicating that the enzyme preparation was pure. The molecular mass of the enzyme determined from SDS-PAGE analysis was 55.0 kDa. Using 2,6-dimethoxyphenol, 2,2′[azino-bis-(3-ethylbonzthiazoline-6-sulphonic acid) diammonium salt] and 3,5-dimethoxy-4-hydroxybenzaldehyde azine as the substrates, the Km, kcat and kcat/Km values of the laccase were found to be 420 μM, 13.04 s−1, 3.11 × 104 M−1 s−1, 225 μM, 13.03 s−1, 1.3 × 105 M−1 s−1 and 100 μM, 13.04 s−1, 5.8 × 104 M−1 s−1, respectively. The pH and temperature optima were 4.5 and 60 °C, respectively while pH and temperature stabilities were pH 4.5 and 50 °C. The activation energy for thermal denaturation of the enzyme was 18.6 kJ/mol/K. The purified laccase has yellow colour and does not show absorption band around 610 nm like blue laccases. The purified laccase transforms toluene, 3-nitrotoluene, 4-nitrotoluene, 3-chlorotoluene, 4-chlorotoluene and 3,4-dimethoxytoluene to benzaldehyde, 3-nitrobenzaldehyde, 4-nitrobenzaldehyde, 3-chlorobenzaldehyde, 4-chlorobenzaldehyde and 3,4-dimethoxybenzaldehyde in the absence of mediator molecules in high yields.