Hydrolytic activity of enzyme derivatives was determined by measuring the increase in absorbance at 348nm produced by the
release of p-nitrophenol during the hydrolysis of p-nitrophenyl butyrate (dissolved in acetonitrile) in 25mMpotassium phosphate
buffer (pH 7.0) at room temperature. To start the reaction, 20–80_l of the lipase suspension (50mg immobilized enzyme in 1 ml phosphate buffer 25mMpH 7) was added to 1ml of the reaction mixture (0.8mM pNPB in phosphate buffer 25mM pH 7). Hydrolysis was followed by measuring the change in absorbance over 2min.