Sara Peirce

Development of simple protocols to solve the problems of enzyme coimmobilization. Application to coimmobilize a lipase and a β-galactosidase

This paper shows the coimmobilization of β-galactosidase from Aspergillus oryzae (β-gal) and lipase B from Candida antarctica (CALB). The combi-biocatalyst was designed in a way that permits an optimal immobilization of CALB on octyl-agarose (OC) and the reuse of this enzyme after β-gal (an enzyme with lower stability and altogether not very stabilized by multipoint covalent attachment) inactivation, both of them serious problems in enzyme co-immobilization. With this aim, OC-CALB was coated with polyethylenimine (PEI) (this treatment did not affect the enzyme activity and even improved enzyme stability, mainly in organic medium). Then, β-gal was immobilized by ion exchange on the PEI coated support. We found that PEI can become weakly adsorbed on an OC support, but the adsorption of PEI to CALB was quite strong. The immobilized β-gal can be desorbed by incubation in 300 mM NaCl. Fresh β-gal could be adsorbed afterwards, and this could be repeated for several cycles, but the amount of PEI showed a small decrease that made reincubation of the OC-CALB–PEI composite in PEI preferable in order to retain the amount of polymer. CALB activity remained unaltered under all these treatments. The combi-catalyst was submitted to inactivation at 60 °C and pH 7, conditions where β-gal was rapidly inactivated while CALB maintained its activity unaltered. All β-gal activity could be removed by incubation in 300 mM NaCl, however, SDS analysis showed that part of the enzyme β-gal molecules remained immobilized on the OC-CALC–PEI composite, as the inactivated enzyme may become more strongly adsorbed on the ion exchanger. Full release of the β-gal after inactivation was achieved using 1 M NaCl and 40 °C, conditions where CALB remained fully stable. This way, the proposed protocol permitted the reuse of the most stable enzyme after inactivation of the least stable one. It is compatible with any immobilization protocol of the first enzyme that does not involve ion exchange as only reason for enzyme immobilization.

Evaluation of different commercial hydrophobic supports for the immobilization of lipases: tuning their stability, activity and specificity

Five different commercial supports (Lifetech™ ECR1061M (styrene/methacrylic polymer), Lifetech™ ECR8804M (octadecyl methacrylate), Lifetech™ ECR8806M (octadecyl methacylate), Lifetech™ ECR1090M (styrene) and Lifetech™ ECR1030M (DVB/methacrylic polymer)) were compared to octyl agarose in their performance in the immobilization of four different lipases (from Rhizomucor miehie (RML), from Thermomyces lanuginosus (TLL) and the forms A and B from Candida antarctica, (CALA and CALB)) and of the phospholipase Lecitase Ultra™ (LU). The new enzymatic derivatives were evaluated and compared with the commercial biocatalyst (Novozym 435 (CALB), Lipozyme RM IM and Lipozyme TL IM). Textural properties, loading capacity, enzyme stability under different conditions, and activity versus different substrates were analyzed. Although all of the supports reversibly immobilized lipases via interfacial activation of lipases versus the hydrophobic surface of the support, some of them permitted a significant improvement in the final biocatalyst compared to the reference support or the commercial preparations. Enzyme specificity depended strongly on the used support (e.g., the new ones gave almost null activity versus p-nitrophenyl butyrate). However, there is not a universal optimal support; the “best” support depends on the enzyme, the parameter studied and the substrate utilized. Nevertheless, under the conditions utilized, the preparations showed a very good performance in a diversity of reactions and permitted their reuse (both the biocatalyst and the supports after eliminating the enzyme by washing the enzyme with triton X-100). These supports will permit enlarging the library of immobilized lipase biocatalyst, being supports useful for aqueous or organic medium.

Stabilization of Candida antarctica Lipase B (CALB) Immobilized on Octyl Agarose by Treatment with Polyethyleneimine (PEI)

Lipase B from Candida antarctica (CALB) was immobilized on octyl agarose (OC) and physically modified with polyethyleneimine (PEI) in order to confer a strong ion exchange character to the enzyme and thus enable the immobilization of other enzymes on its surface. The enzyme activity was fully maintained during the coating and the thermal stability was marginally improved. The enzyme release from the support by incubation in the non-ionic detergent Triton X-100 was more difficult after the PEI-coating, suggesting that some intermolecular physical crosslinking had occurred, making this desorption more difficult. Thermal stability was marginally improved, but the stability of the OCCALB-PEI was significantly better than that of OCCALB during inactivation in mixtures of aqueous buffer and organic cosolvents. SDS-PAGE analysis of the inactivated biocatalyst showed the OCCALB released some enzyme to the medium during inactivation, and this was partially prevented by coating with PEI. This effect was obtained without preventing the possibility of reuse of the support by incubation in 2% ionic detergents. That way, this modified CALB not only has a strong anion exchange nature, while maintaining the activity, but it also shows improved stability under diverse reaction conditions without affecting the reversibility of the immobilization.

Immobilization of carbonic anhydrase for biomimetic CO 2 capture in a slurry absorber as cross-linked enzyme aggregates (CLEA)

Novel post-combustion Carbon Capture and Storage (CCS) processes include absorption of CO 2 into aqueous solutions assisted by enzyme catalysis. Carbonic anhydrase EC 4.2.1.1 (CA) catalyzes CO 2 hydration and it has been proposed as industrial biocatalyst for biomimetic CCS processes. The present study reports on the use of bovine CA immobilized via cross-linking of enzyme aggregates (CLEA). The aim of this study was to improve the biocatalyst stability at the typical operating conditions of CCS processes (high temperature, alkaline pH, high salt concentration). The optimum conditions of the immobilization procedure were determined in terms of enzyme concentration and cross-linker concentration. In addition, a magnetic CLEA (m-CLEA) sample was prepared, based on cross-linking in presence of amino-functionalized paramagnetic nanoparticles. Immobilization yields was remarkable in both cases. No substantial differences were observed between conventional and magnetic CLEA. The use of magnetic CLEA enables effective separation of the biocatalyst from the reaction mixture and prevent drawbacks associated with CLEA aggregation and compaction induced by centrifugation and filtration.