The number of laccase isoenzymes and laccase activities of Pleurotus ostreatus in buffered and non-buffered media were determined. In both culture media, the initial pH was adjusted to 3.5. Similar laccases activity (100-500 U/L) was observed in the range of 100-400 h (approximately) of fermentation in both media. Buffered culture medium yielded higher laccases activities (3200 U/L) at 500 h of fermentation than those observed in non-buffered culture medium (450 U/L). One laccase isoenzyme was produced during the entire fermentation process in both media. In the non-buffered medium, an additional isoenzyme of lower molecular weight than that produced in the entire fermentation process was produced at the beginning of the exponential phase of growth when the pH reached a value of 6.5. These results suggest that the fungus produces metabolites that modify the pH of the medium and that some laccases isoenzymes are regulated by pH signals. This is the first report on zymogram patterns from laccases activity of P. ostreatus at low pH.
Key words: Laccases, fermentation, Pleurotus ostreatus, zymogram.
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