Use of polyethylenimine to produce immobilized lipase multilayers biocatalysts with very high volumetric activity using octyl-agarose beads: Avoiding enzyme release during multilayer production.

A strategy to obtain biocatalysts formed by three enzyme layers has been designed using lipases A and B from Candida antarctica (CALA and CALB), the lipases from Rhizomucor miehei (RML) and Thermomyces lanuginosus (TLL), and the artificial chimeric phospholipase Lecitase Ultra (LEU). The enzymes were initially immobilized via interfacial activation on octyl-agarose beads, treated with polyethylenimine (PEI) and a new enzyme layer was immobilized on the octyl-enzyme-PEI composite by ion exchange, producing octyl-enzyme-PEI-enzyme biocatalysts. Except when using LEU, when the two-layer biocatalysts, a large percentage of the PEI-immobilized enzyme was released when a new batch of PEI was added. This was prevented by glutaraldehyde crosslinking. The enzyme modifications produced more active preparations in some cases while in other cases, the effect of the modifications was negative for enzyme activity. These effects of the enzymes modifications were also different when the enzyme was immobilized by interfacial activation or by ion exchange. In all cases, the 3-layer biocatalysts were more active than the single- or bi-layer biocatalysts with some of the assayed substrates. However, as the substrate diffusion problems increased when new enzyme layers were added, even a decrease in enzyme activity with some substrates was found after increasing the number of enzyme layers.

Effects of Enzyme Loading and Immobilization Conditions on the Catalytic Features of Lipase From Pseudomonas fluorescens Immobilized on Octyl-Agarose Beads.

The lipase from Pseudomonas fluorescens (PFL) has been immobilized on octyl-agarose beads under 16 different conditions (varying pH, ionic strength, buffer, adding some additives) at two different loadings, 1 and 60 mg of enzyme/g of support with the objective of check if this can alter the biocatalyst features. The activity of the biocatalysts versus p-nitrophenyl butyrate and triacetin and their thermal stability were studied. The different immobilization conditions produced biocatalysts with very different features. Considering the extreme cases, using 1 mg/g preparations, PFL stability changed more than fourfolds, while their activities versus pNPB or triacetin varied a 50-60%. Curiously, PFL specific activity versus triacetin was higher using highly enzyme loaded biocatalysts than using lowly loaded biocatalysts (even by a twofold factor). Moreover, stability of the highly loaded preparations was higher than that of the lowly loaded preparations, in many instances even when using 5°C higher temperatures (e.g., immobilized in the presence of calcium, the highly loaded biocatalysts maintained after 24 h at 75°c a 85% of the initial activity, while the lowly loaded preparation maintained only 27% at 70°C). Using the highly loaded preparations, activity of the different biocatalysts versus pNPB varied almost 1.7-folds and versus triacetin 1.9-folds. In this instance, the changes in stability caused by the immobilization conditions were much more significant, some preparations were almost fully inactivated under conditions where the most stable one maintained more than 80% of the initial activity. Results suggested that immobilization conditions greatly affected the properties of the immobilized PFL, partially by individual molecule different conformation (observed using lowly loaded preparations) but much more relevantly using highly loaded preparations, very likely by altering some enzyme-enzyme intermolecular interactions. There is not an optimal biocatalyst considering all parameters. That way, preparation of biocatalysts using this support may be a powerful tool to tune enzyme features, if carefully controlled.

Coimmobilization of different lipases: Simple layer by layer enzyme spatial ordering.

This paper shows the step by step coimmobilization of up to five different enzymes following two different orders in the coimmobilization to alter the effect of substrate diffusion limitations. The enzymes were the lipases A and B from Candida antarctica, the lipases from Rhizomocur miehei and, Themomyces lanuginosus and the phospholipase Lecitase Ultra. The utilized strategy was a layer by layer immobilization, coating the immobilized enzymes with polyethylenimine followed by the crosslinking of the enzyme and PEI with glutaraldehyde to prevent enzyme release, and them adding a new lipase layer. The use of previously inactivated biocatalysts (using diethyl p-nitrophenylphosphate) permitted to visualize the immobilization of each enzyme layer, which was later confirmed by SDS-PAGE. This also confirmed the successful and complete covalent crosslinking of the glutaraldehyde treated enzyme layers. Activity of the combibiocatalysts was followed using diverse substrates. The protocol was successful and permitted to immobilize in an ordered way the 5 different enzymes in a down-up distribution.

Modulating the properties of the lipase from Thermomyces lanuginosus immobilized on octyl agarose beads by altering the immobilization conditions.

The lipase from Thermomyces lanuginosus (TLL) has been immobilized on octyl-agarose beads via interfacial activation under 16 different conditions (changing the immobilization pH, the ionic strength, the presence of additives like calcium, phosphate or glycerol) and using a low loading (1 mg/g support). Then, the properties of the different biocatalysts have been evaluated: stability at pH 7.0 and 70 °C and activity versus p-nitro phenyl propionate, triacetin and R- and S- methyl mandelate. Results clearly indicate that the immobilization conditions determine the final enzyme properties, altering enzyme stability (by 10 folds), activity (by 8 folds using R- methyl mandelate) and specificity (VR/VS changed from 0.7 to 2.3 using mandelate esters). For instance, the enzymes immobilized at pH 7.0 using 5 mM buffer were the most stable preparations, while the presence of 250 mM sodium phosphate greatly decreased the final enzyme stability. The biocatalyst stability of TLL increased with increasing NaCl in the immobilization buffer at pH 5. Fluorescence studies confirmed that the conformation of the different immobilized enzymes were different, despite being a physical and reversible immobilization method. Thus, the immobilization of TLL on octyl agarose beads under different conditions produced biocatalysts with different properties, the optimal condition depends on the studied reaction and condition.

Immobilization of lipase from Pseudomonas fluorescens on glyoxyl-octyl-agarose beads: Improved stability and reusability.

The lipase from Pseudomonas fluorescens (PFL) has been immobilized on glyoxyl-octyl agarose and compared to the enzyme immobilized on octyl-agarose. Thus, PFL was immobilized at pH 7 on glyoxyl-octyl support via lipase interfacial activation and later incubated at pH 10.5 for 20 h before reduction to get some enzyme-support covalent bonds. This permitted for 70% of the enzyme molecules to become covalently attached to the support. This biocatalyst was slightly more stable than the octyl-PFL at pH 5, 7 and 9, or in the presence of some organic solvents (stabilization factor no higher than 2). The presence of phosphate anions produced enzyme destabilization, partially prevented by the immobilization on glyoxyl-octyl (stabilization factor became 4). In contrast, the presence of calcium cations promoted a great PFLstabilization, higher in the case of the glyoxyl-octyl preparation (that remained 100% active when the octyl-PFL preparations had lost 20% of the activity). However, it is in the operational stability where the new biocatalyst showed the advantages: in the hydrolysis of 1 M triacetin in 60% 1.4 dioxane, the octyl biocatalyst released >60% of the enzyme in the first cycle, while the covalently attached enzyme retained its full activity after 5 reaction cycles.

New applications of glyoxyl-octyl agarose in lipases co-immobilization: Strategies to reuse the most stable lipase.

Lipase B from Candida antarctica (CALB), lipase from Rhizomucor miehei (RML) and phospholipase Lecitase Ultra (LEU) were immobilized via interfacial activation and their stabilities were compared. Immobilized CALB was much more stable than immobilized RML or LEU. That meant that, if they were coimmobilized, after the inactivation of the least stable lipases, CALB should be discarded even though it may maintain full activity. This could be solved by sequential coimmobilization on octyl-glyoxyl (OCGLX). First, CALB was immobilized on OCGLX getting some covalent bonds between most of the CALB molecules and the support. Then, after reduction of CALB immobilized on OCGLX, RML or LEU can be immobilized on the support via interfacial activation. These enzymes could be released from the support just by using detergents, without affecting CALB activity. After optimization of the lipase desorption conditions, the bi-combilipases CALB/RML and CALB/LEU or the triple-combilipase CALB/RML/LEU could be submitted to several cycles of immobilized biocatalyst inactivation, desorption and enzyme reloading keeping the activity of the immobilized CALB almost intact. This way, by using OCGLX and a stepwise immobilization protocol, discarding all coimmobilized lipases when one becomes inactivated is no longer required. Thus, the most stable ones can be reused in several cycles.

Chitosan activated with divinyl sulfone: a new heterofunctional support for enzyme immobilization. Application in the immobilization of lipase B from Candida antarctica.

A novel heterofunctional support for enzyme immobilization, chitosan-divinyl sulfone, was assessed in this study. The activation of chitosan with DVS was carried out at three different pHs (10.0, 12.5 and 14.0) and a Candida antarctica Lipase B (CALB) was selected as the model enzyme. After immobilization, the biocatalysts were incubated under alkaline conditions in a buffer to facilitate the multipoint covalent attachment, followed by incubation in ethylenediamine (EDA) aiming at blocking the remaining reactive groups. The highest thermal stability was obtained when pH 10.0 was used during support activation. These results were shown to be better than those obtained when using glutaraldehyde as the support-activating reagent. Subsequently, the immobilization pH was investigated (5.0, 7.0 and 10.0) prior to alkaline incubation, with the highest enzyme stability levels found at pH 10.0. Finally, the selected biocatalyst was used in the hydrolysis of ethyl hexanoate and presented an activity of 14,520.37 U/g of immobilized lipase at pH 5.0. These results show that chitosan activated with divinyl sulfone is a very promising support for enzyme immobilization and the proposed protocol is able to successfully improve enzyme stability.