Kinetic Properties and Enantioselectivity of The Lipases Produced by Four Aspergillus Species

Abstract

Four high lipase-producing Aspergillus species, selected in our laboratory, were compared in terms of their stability and reactivity for enantioselective esterification between (R, S)-2-octanol with octanoic acid in n-hexane. We determined the pH and temperature reactions dependences of lipases activities, and we found that these enzymes exhibited various pH sensitivities. The optimum pH observed for Aspergillus terreus lipase was 5.5, for A. niger and A. oryzae lipases in the range of 6.0 to 6.5 and pH 7.0 for A. flavus lipase. Good stability was observed at pH ranging from 5.0 to 8.5 after 24 hours at 40° C, and the optimum activity was observed at 35–40° C for all lipases tested. The lipases from A. terreus and A. niger were highly thermostable, retaining 60% and 50% activity at 60° C after 1 hour, respectively. The lipases from A. niger and A. terreus lipases provided the best results in terms of enantioselectivity (E) in the esterification of (R, S)-2-octanol with octanoic acid in n-hexane (E = 4.9 and E = 4.5, respectively). These properties make these lipases good candidates for biocatalysis in organic media.

Key Words:

• Lipase
• Aspergillus sp
• enantioselectivity

5. ACKNOWLEDGEMENTS

This work was supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) of Brasil. We wish thank Dr. M. do C. Basílio (ITQB/UNL) and Dr. J. L. B. Ferreira from the Centro de Micologia da Universidade de Lisboa (Portugal), for identification of the strains.

Notes

^aGrowth media (w/v): glucose 1.0%, 2% peptone, 0.5% yeast extract, 0.1% NaNO₃, 0.1%, KH₂PO₄ 0.05% MgSO₄. 7H₂O and 2% of olive oil.

^bbiomass weight was derived from 100 ml of the medium (p < 0.05).

^clipase activity U/mL liquid crude extract (p < 0.05).

^dtotal protein content in crude extract (p < 0.05).

^eSpecific activity in U/ mg of total protein.

^aEster yield is given as the porcentage of initial alcohol esterificated after the reaction time (p < 0.05).

^bEnantiomeric excess of remaining alcohol (S-octanol) (p < 0.05).

^cEnantiomeric Ratio (p < 0.05).