First description of a laccase-like enzyme in soil algae

Laccases (EC 1.10.3.2) are versatile multi-copper oxidases so far found in higher plants, fungi, insects, prokaryotes and lichens. In the present study, the production of an extracellular laccase-like enzyme by the coccoid green soil alga Tetracystis aeria was investigated and the enzyme was partly characterized, thereby providing the first description of a laccase-like enzyme in soil algae. Enzyme production in algae cultures was considerably increased by addition of the fungal laccase inducer copper sulphate. Maximal enzyme production was observed during the stationary growth phase. Peroxidase or tyrosinase activity was not detected. The native enzyme exhibits an apparent molecular mass of about 212 kDa as observed with size exclusion chromatography and about 210-260 kDa as estimated by zymograms. The enzyme efficiently oxidizes 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), 2,6-dimethoxyphenol (2,6-DMP), syringaldazine (SGZ) and the anthraquinone dye Acid Blue 62, while guaiacol and Remazol Brilliant Blue R are only poorly oxidized. The apparent kinetic parameters obtained for ABTS, 2,6-DMP and SGZ oxidation are within the range reported for fungal laccases. Oxidation of the phenolic substrate 2,6-DMP displays a remarkably high pH optimum (pH 8.0-8.5), which is interesting with respect to potential biotechnological applications.