Activity And Enantioselectivity Of Modified Lipases In Organic Solvents

Lipases From Rhizomucor michci and Candida antarctica component B (Ca1B), 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 enantioselectivity of Ca1B 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 enantio-selectivity. Whereas MPEG modification increased the enantioselectivity of Ca1B, modification with OPEG and OCT decreased the enantioselectivity as compared to native Ca1B. With higher degrees of modification both activity and enantioselectivity increased. The enthalpic and entropic contributions to the enantioselectivity, Delta Delta H-R-S(#) and Delta Delta(SR-S)(#) were calculated from the E-values measured at various temperatures. No clear correlation was observed between Delta Delta H-R-S(#) or Delta S-R-S(#) and the degree of modification, structure or hydrophobicity of the modifier. Linear enthalpy-entropy compensation was observed for the different Ca1B species. 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.