IMMOBILIZATION OF LIPASE ON POLYSULFONE MEMBRANES

Abstract

Polysulfone has been used widely for making ultrafiltration membranes due to its good stability and membrane forming properties. In this project, lipase was covalently attached to -COOH groups on carboxylated polyeulfone (cPSf) membrane. -COOH groups of cPSf were activated by either N-ethoxycarbonyl-2- ethoxy-1,2-dihydroquinoline (EEDQ) or by the MHG method, which comprises a series of treatment with acidified methanol, hyhrazine and glutaraldehyde. The EEDQ treated cPSf can undergo further treatment with hexadiamine to extend the spacer length. 6-aminohexanoic acid and lipase were successfully coupled to cPSf. Experimental results showed that the higher the degree of carboxylation (DC), the higher the number of active groups formed after treatment with EEDQ and MHG. For the attachment of 6-arninohexanoic acid, cPSf of higher DC yielded a higher loading of the amino acid on the activated cPSf. Larger membrane pore size and crosslinking by glutaraldehyde also enhanced the amino acid loading. cPSf activated by EEDQ yielded a higher loading than cPSf activated by the MHG method. In the immobilisation of lipase, specific lipase activity increased with DC of cPSf, though lipase loading on cPSf was not significantly affected by its DC. The presence of substrate during coupling decreased the lipase loading on cPSf. A longer spacer length did not serve to increase the activity of the immobilised lipase. Crosslinking by glutaraldehyde enhanced the lipase loading but greatly reduced the specific lipase activity. However crosslinking treatment helped to retain a higher percentage of the initial lipase activity on subsequent lipase activity assay. EEDQ activated cPSf membrane generally yielded a higher lipase activity than cPSf treated with MHG method.