Effects of additives on the activity of a covalently immobilised lipase in organic media

Lipase from Mucor miehei was covalently immobilised onto the graft copolymer poly(ethylene)-g.co-hydroxyethyl methacrylate (EE-g.co-HEMA), partially hydrolysed, via a spacer arm of 1,6-diaminohexane activated with glutaraldehyde. To improve the lipolytic activity of the immobilised lipase (for the synthesis of isoamyl-caprylate, as a model), the effect of several additives was investigated. Polyethylene glycol (PEG), glutaraldehyde, organic solvents and buffers, were added during the immobilisation procedure and their effects are reported and compared with the behaviour of the lipolytic preparation without pre-treatment. An increase of 40-100% in the activity was obtained when small quantities of PEG 2000 and glutaraldehyde (used also as an activator of the spacer arm) were added. The activity had a maximum when the pH of the lipase attachment solution was 7.2 and buffered with phosphate. The effect of the aggregation level of biocatalyst particles on the amount of water retained, as well as the effect of the immobilisation on solid supports on the stability to organic solvents, is also reported. (C) 1998 Elsevier Science B.V. All rights reserved.