Designing cross-linked lipase aggregates for optimum performance as biocatalysts

Cross-linked enzyme aggregates (CLEAs)are prepared by precipitation of an enzyme and then chemical cross-linking the precipitate. Three CLEAs of lipase with glutaraldehyde concentrations of 10 mM (CLEA A), 40 mM (CLEA B)and 60 mM (CLEA C)were prepared. Studies show that there is a trade-off between thermal stability vs transesterification/ hydrolysis rate vs enantioselectivity. The initial rates for transesterification of b-citronellol for the uncross-linked enzyme and CLEAs A, B and C were 243, 167, 102 and 40 mmol mg 1 h 1, respectively. Their thermal stabilities in aqueous media, as reflected by their half-life values at 558C, were 6, 9, 13 and 16 h, respectively. The enantioselectivity, E values (for kinetic resolution of b-citronellol by transesterification)were 19, 74, 11 and 6, respectively. These results show that CLEA C was the most thermostable; the uncross-linked enzyme was best at obtaining the highest transesterification rate; and CLEA A was best suited for the enantioselective synthesis. Scanning electron microscopy (SEM)showed that the morphology of CLEA was dependent upon the extent of cross-linking.