Abstract
A native isolate of Pleurotus ostreatus HP-1 (Genbank Accession No. EU420068) was found to have an excellent laccase producing ability. The extracellular laccase was purified to electrophoretic homogeneity from copper sulphate induced solid-state fermentation medium by ammonium sulphate precipitation and ion-exchange chromatography. The enzyme was determined to be monomeric protein with an apparent molecular mass of 68,420 kDa, and an isoelectric point (pI) of 3.5. The inductively coupled plasma spectroscopy showed a presence of iron, zinc and copper in the purified enzyme. The absorption spectrum in the range of 200–700 nm showed the maximum absorption at 610 nm characteristic of fungal laccase and corresponding to the presence of type I copper atom. The laccase was stable at different temperatures up to 70 °C and retained 61 % activity at 50 °C. The enzyme reaction was inhibited by cysteine; sodium azide and EDTA. The enzyme oxidized various known laccase substrates, its lowest Km value being for ortho-dianisidine and highest Kcat and Kcat/Km for ABTS. The purified laccase exhibited different pH optima for different substrates. The N-terminal sequence did not show any similarity with N-terminal sequence of other species of genera Pleurotus.
Highlights
Laccases are multinuclear copper-containing enzymes that catalyse the oxidation of a variety of phenolic and inorganic compounds, with the concomitant reduction of oxygen to water
The appropriate knowledge about structural and functional properties of P. ostreatus HP-1 laccases will further help in the elucidation of physiological function of this enzyme
Optimum culture conditions were used for the production of laccase from P. ostreatus HP 1 (Genbank Accession No EU420068) as described in our earlier study (Patel et al 2009)
Summary
Laccases (benzenediol: oxygen oxidoreductase, E.C. 1.10.3.2) are multinuclear copper-containing enzymes that catalyse the oxidation of a variety of phenolic and inorganic compounds, with the concomitant reduction of oxygen to water. Laccases are widely distributed in nature and have been detected in plants, insects, bacteria and especially in fungi (Majeau et al 2010). These oxidative enzymes are abundant in white-rot Basidiomycete fungi, which are capable of degrading lignin in vivo. Fungal laccases have ability in the degradation of toxic fungal metabolite, such as aflatoxin B1, in ethanol production, manufacturing of cream and wine clarification. These characteristics have led to laccases being qualified as ‘‘eco-friendly’’ enzymes (Alberts et al 2009; Lu et al 2007). The appropriate knowledge about structural and functional properties of P. ostreatus HP-1 laccases will further help in the elucidation of physiological function of this enzyme
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