The ultra-violet visible (UV/Vis) absorption spectrum of laccase was similar to that observed of other fungal laccases (Coll et al. 1993; Eggert et al. 1996) with a Type I band at 614 nm, corresponding to the blue copper of laccases (Reinhammer and Malstrom 1981) and a broad band at 330 nm indicative of a Type III binuclear copper center (Malkin et al. 1969; Reinhammer 1984). The EPR spectrum of purified laccase had two superimposed signals of Type I and Type II copper centers.
The laccase was stable at 60°C for1 h and still retained much activity after 2 h incubation at 80°C. It differed from the laccase of P. cinnabarinus PB (Eggert et al. 1996) which was inactivated after incubation at 80°C for 1 h. The enzyme was still active in bioreactors run at 37°C for 25 days but lost activity on prolonged treatment at the higher temperatures.
The pH optimum for syringaldazine was between pH 4.4 and 5 and for guaiacol between pH 4 and 4.5. The Km was
0.03 mM for syringaldazine and 0.33 mM guaiacol. Activity was irreversibly inhibited by 0.1 mM sodium azide and by ascorbic acid at 1 mM.
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