RESUMO
An isolate of Coriolus hirsutus constitutively expresses substantial amounts of extracellular laccase on a defined growth medium. The most efficient inducer of extracellular laccase synthesis was syringaldazine, which increased the enzyme yield by 1000% at a concentration of 0.11 microM. The constitutive form of the enzyme was purified 312-fold. Laccase from C. hirsutus, with an estimated molecular mass of 55 kDa and pI of 4.0, is a monomeric glycoprotein containing 12% carbohydrate consisting of mannose and N-acetylglucosamine. The laccase was found to contain 3.9-4.1 copper atoms per molecule. The absorption spectrum shows a maximum at 610 nm and a shoulder at 330 nm, which is typical of laccase possessing type 1 and type 3 copper atoms. The parameters of the first type of copper were determined by EPR as g perpendicular=2.046 and g parallel=2.200, A parallel=8.103 x 10(-3) cm-1. Laccase was found to be a pH-stable and thermostable enzyme. With organic substrates it exhibits a pH optimum of 4.5, but with the inorganic substrate K4[Fe(CN)6] this decreased to 3.5. The highest efficiency of catalysis was observed with sinapinic acid as the substrate. The kinetic constants kcat and Km of this reaction were 578 s-1 and 24 microM respectively. It was established that the kinetics of the assayed reaction shows a Ping Pong mechanism.