Activity And Enantioselectivity Of Modified Lipases In Organic Solvents

Abstract

Lipases from Rhizomucor miehei and Candida antarctica component B (CalB), and cutinase from Fusarium solani pisi were chemically modified with tresyl activated polyethylene glycol monomethyl ether (MPEG). The enantioselectivity of the native and the modified lipases in the transesterification reaction of three different chiral alcohols was measured in o-xylene and tert-butyl methyl ether at the optimal water activities. Both activity and enantioselectivity changed upon modification of the enzymes. To study the effect of the hydrophobicity of the modifier and degree of modification on the activity and enantioselcctivity of CalB in more depth, this lipase was chemically modified with MPEG, polyethylene glycol monooctyl ether (OPEG) and n-octanol (OCT). The hydrophobicity of the modifier had a profound effect on the enantioselectivity. Whereas MPEG modification increased the cnantioselectivity of CalB, modification with OPEG and OCT decreased the enantioselectivity as compared to native CalB. With higher degrees of modification both activity and enantioselectivity increased. The enthalpic and en tropic contributions to the enantioselectivity, ΔΔH#R-S, and ΔΔS#R-S, were calculated from the E-values measured at various temperatures. No clear correlation was observed between ΔΔH#R-S or ΔΔS#R-S, and the degree of modification, structure or hydrophobicity of the modifier. Linear enthalpy-entropy compensation was observed for the different CalB spccies.The present results indicate that, in order to increase enzyme activity and enantioselectivity, a modifier should be used which positively affects the porosity of the enzyme aggregates or enzyme flexibility. Also higher degrees of modification are preferred.