Activity and stability of a crude lipase from Penicillium aurantiogriseum in aqueous media and organic solvents

Abstract

The effects of various environmental conditions and chemical compounds on the activity and stability of the lipolytic preparation obtained from a wild strain of Penicillium aurantiogriseum were characterized during a preliminary evaluation of its potential for use in biocatalysis. In aqueous solution, the optimum pH for activity was 8.0 and the enzyme was stable between pH 6.0 and pH 9.0. In assays of 1 min duration carried out at pH 8.0, enzyme activities were quite high from 37 to 70 °C, with a maximum at 60 °C. However, thermal stability was rather low at temperatures higher than 28 °C. Hydrolytic activity was enhanced by Mg 2+, Zn 2+, Co 2+ and Mn 2+, but was inhibited by Cu 2+, Ba 2+ and Hg 2+, while Ca 2+ had no effect. Sodium azide activated the enzyme. Triton X-100 caused an inhibition of 52%, while Tween 80 and SDS had negligible effects on enzymatic activity. Despite the low ratio of the activity towards p-nitrophenyl palmitate (pNPP) in organic medium to that in aqueous medium ( R O/A=4.3×10 −2), the enzyme showed a good stability in organic solvents with high log P values, the best result being in n-heptane (114% residual activity). These promising results with the crude preparation justify the undertaking of purification studies and the use of the pure enzyme in a more in-depth investigation for its potential in biocatalysis in organic solvents.