Stabilization of different alcohol oxidases via immobilization and post immobilization techniques

The thermal stability of multimeric alcohol oxidases (AOXs) from three different sources (Candida boidinii, Hansenula sp. and Pichia pastoris) was evaluated. AOX from C. boidinii was markedly more unstable than the other two enzymes, while the enzyme from Hansenula sp. was the most stable of the three. The stability of the enzymes was strongly dependent on the enzyme concentration, suggesting that the first inactivation cause could be subunits dissociation. The two most stable enzymes were immobilized through different immobilization methodologies (covalent and ionic adsorption techniques). The best results in terms of stability were obtained when the enzymes were covalently immobilized in glyoxyl agarose. However, with this strategy the quaternary structure of these enzymes could not be fully stabilized. Thus, dextran aldehyde was used to cross-link the enzyme subunits not attached to the support. Although this treatment prevents dissociation of the enzyme subunits and avoids the effect of enzyme concentration on the stability of both enzymes, the final activity recovery in both cases was below 20%. The other very stabilizing immobilization protocol for both enzymes was the ionic adsorption on agarose coated with 600 kDa polyethylenimine. The adsorption of the proteins on the polymeric bed allowed the stabilization of the quaternary structure: the effect of the enzyme concentration on thermal enzyme stability disappeared in these immobilized preparations. Thus, a high stability was obtained without a significant decrease in enzyme activity during immobilization (recovered activity was over 50%).