Effects of additives on the activity and enantioselectivity of Candida rugosa lipase a in a biphasic medium

Abstract

The effects of Li+, Na+, K+, Mg2+ and Zn2+ ions on the activity and enantioselectivity of Candida rugosa lipase (CRL) were investigated in a biphasic medium composed of phosphate buffer solution (containing a metal ion within a 50-500 mM concentration range) and isooctane. The hydrolytic activities of CRL towards p-nitrophenyl acetate were measured after incubation of the enzyme in the presence of metal ions for 24 h, and they were compared to that obtained after incubation in the absence of any metal ion. The CRL activity was stimulated by the chloride salts of Li+, K+ and Mg2+ for all concentrations considered and the highest enhancement was achieved by Li+ with a 1.24-1.75 fold increase observed. The effects of metal ions on the enantioselectivity of CRL were investigated by performing the hydrolysis of racemic Naproxen methyl ester in the same biphasic medium containing Li+, Na+, K+, Mg2+ and Zn2+ ions. The addition of metal ions increased the hydrolysis rate by ca. 1.31-1.45 fold relative to the control, whereas the enantiomeric excess of product increased slightly in the presence of the metal ions. The effect of Triton X-100 on the activity and enantioselectivity of the CRL was also investigated by employing 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 mM concentrations of it in phosphate buffer solution of the biphasic medium. High concentrations of Triton X-100 stimulated the enzyme activity up to 1.66 fold after 24 h incubation. Triton X-100 increased the hydrolysis rate almost independently of the concentration.