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.

The effect of an additive on enzyme stability used to be considered an intrinsic feature of a lipase. However, in this paper we have found that the effect of additive on enzyme stability depends on the immobilization protocol. After assaying the effects of diverse chloride salts with different cations on different lipases activity, no relevant effect was detected. Free enzymes or the covalently immobilized enzymes are not stabilized by these cations for any of the studied lipases. However, Mn²⁺ and Ca²⁺ (at a concentration of 5 mM) are able to greatly stabilize the lipases from Rhizomucor miehei (RML) and Candida rugosa (CRL) when they are present during the inactivation, but only if the enzymes are immobilized on octyl-agarose (stabilization factor ranging from 20 to 50). The effect was only detected when using more than 2.5 mM of the cations, and reached the maximum value at 5 mM, suggesting a saturation mechanism of action. The stabilization seemed to be based on a specific mechanism, and required the recognition sites to be saturated by the cations. Mg²⁺ has no effect on enzyme stability for both enzymes, but it is able to suppress the stabilization promoted by the other two cations using CRL; while it has no effect on the cation stabilization when using RML. This is the first report of a cation induced enzyme stabilization effect that depends on the lipase immobilization protocol.