Adsorption features of reduced aminated supports modified with glutaraldehyde: Understanding the heterofunctional features of these supports

Immobilization of enzymes on aminated supports using the glutaraldehyde chemistry may involve three different interactions, cationic, hydrophobic, and covalent interactions. To try to understand the impact this heterofunctionality, we study the physical adsorption of the beta-galactosidase from Aspergillus niger, on aminated supports (MANAE) and aminated supports with one (MANAE-GLU) or two molecules of glutaraldehyde (MANAE-GLU-GLU). To eliminate the chemical reactivity of the glutaraldehyde, the supports were reduced using sodium borohydride. After enzyme adsorption, the release of the enzyme from the supports using different NaCl concentrations, Triton X100, ionic detergents (SDS and CTAB), or different temperatures (4 °C to 55 °C) was studied. Using MANAE support, at 0.3 M NaCl almost all the immobilized enzyme was released. Using MANAE-GLU, 0.3 M, and 0.6 M NaCl similar results were obtained. However, incubation at 1 M or 2 M NaCl, many enzyme molecules were not released from the support. For the MANAE-GLU-GLU support, none of the tested concentrations of NaCl was sufficient to release all enzyme bound to the support. Only using high temperatures, 0.6 M NaCl, and 1 % CTAB or SDS, could the totality of the proteins be released from the support. The results shown in this paper confirm the heterofunctional character of aminated supports modified with glutaraldehyde.

Prebiotic effect of sorghum biomass xylooligosaccharides employing immobilized endoxylanase from Thermomyces lanuginosus PC7S1T

Purified endoxylanase from Thermomyces lanuginosus PC7S1T was immobilized in calcium alginate, resulting in a yield of 78.5% and a reusability for 11 cycles. The stability of the immobilized enzyme was given for a pH range of 4 to 9 for 96 h. Endoxylanase immobilized in calcium alginate at 65 °C exhibited thermal stability equal to the soluble enzyme for 5 h, and at high temperatures of 75 °C and 85 °C showed half-lives of 4 and 3 h, respectively. Both soluble endoxylanase and immobilized forms were able to hydrolyze hemicellulose, obtained from low-lignin sorghum biomass pretreated with 5% H₂O₂ and 2% NaOH, after 1 h of incubation at 65 °C, releasing a mixture of short-chain xylooligosaccharides (X2-X6). The highest amounts of XOS generated were those for X5 (24 to 40%), X4 (33 to 39%), and X3 (11 to 22%). These XOS acted as prebiotics, promoting the growth of the probiotic L. acidophilus, similar to glucose in the MRS broth. These results show the potential of low-lignin sorghum to generate XOS with prebiotic activity, suggesting the application of these compounds in the food industry.

Effect of Tris Buffer in the Intensity of the Multipoint Covalent Immobilization of Enzymes in Glyoxyl-Agarose Beads

Tris is an extensively used buffer that presents a primary amine group on its structure. In the present work trypsin, chymotrypsin and penicillin G acylase (PGA) were immobilized/stabilized on glyoxyl agarose in presence of different concentrations of Tris (from 0 to 20 mM). The effects of the presence of Tris during immobilization were studied analyzing the thermal stability of the obtained immobilized biocatalysts. The results indicate a reduction of the enzyme stability when immobilized in the presence of Tris. This effect can be observed in inactivations carried out at pH 5, 7, and 9 with all the enzymes assayed. The reduction of enzyme stability increased with the Tris concentration. Another interesting result is that the stability reduction was more noticeable for immobilized PGA than in the other immobilized enzymes, the biocatalysts prepared in presence of 20 mM Tris lost totally the activity at pH 7 just after 1 h of inactivation, while the reference at this time still kept around 61 % of the residual activity. These differences are most likely due to the homogeneous distribution of the Lys groups in PGA compared to trypsin and chymotrypsin (where almost 50% of Lys group are in a small percentage of the protein surface). The results suggest that Tris could be affecting the multipoint covalent immobilization in two different ways, on one hand, reducing the number of available glyoxyl groups of the support during immobilization, and on the other hand, generating some steric hindrances that difficult the formation of covalent bonds.

Effect of amine length in the interference of the multipoint covalent immobilization of enzymes on glyoxyl agarose beads

Trypsin, chymotrypsin, penicillin G acylase and ficin extract have been stabilized by immobilization on glyoxyl agarose, adding different aliphatic compounds bearing a primary amine group during the immobilization: ethyl amine, butyl amine, hexyl amine (at concentrations ranging from 0 to 20 mM) and octyl amine (from 0 to 10 mM) to analyze their effects on the immobilized enzyme stability. As expected, the presence of amines reduced the intensity of the enzyme-support multipoint covalent attachment, and therefore the enzyme stability. However, it is clear that this effect is higher using octyl amine for all enzymes (in some cases the enzyme immobilized in the presence of 10 mM octyl amine was almost inactivated while the reference kept over 50 % of the initial activity). This way, it seems that the most important effect of the presence of aminated compounds came from the generation of steric hindrances to the enzyme/support multi-reaction promoted by the ammines that are interacting with the aldehyde groups. In some instances, just 1 mM of aminated compounds is enough to greatly decrease enzyme stability. The results suggested that, if the composition of the enzyme extract is unknown, to eliminate small aminated compounds may be necessary to maximize the enzyme-support reaction.

Preparation of immobilized/stabilized biocatalysts of β-glucosidases from different sources: Importance of the support active groups and the immobilization protocol

β-Glucosidases from two different commercial preparations, Pectinex Ultra SP-L and Celluclast® 1.5L, were immobilized on divinylsulfone (DVS) supports at pH 5.0, 7.0, 9.0, and 10. In addition, the biocatalysts were also immobilized in agarose beads activated by glyoxyl, and epoxide as reagent groups. The best immobilization results were observed using higher pH values on DVS-agarose, and for Celluclast® 1.5L, good results were also obtained using the glyoxil-agarose immobilization. The biocatalyst obtained using Pectinex Ultra SP-L showed the highest thermal stability, at 65°C, and an operational stability of 67% of activity after 10 reuses cycles when immobilized on DVS-agarose immobilized at pH 10 and blocked with ethylenediamine. The β-glucosidase from Celluclast® 1.5L produced best results when immobilized on DVS-agarose immobilized at pH 9 and blocked with glycine, reaching 7.76-fold higher thermal stability compared to its free form and maintaining 76% of its activity after 10 successive cycles. The new biocatalysts obtained by these protocols showed reduction of glucose inhibition of enzymes, demonstrating the influence of immobilization protocols, pH, and blocking agent.

Characterization of a novel Aspergillus niger beta-glucosidase tolerant to saccharification of lignocellulosic biomass products and fermentation inhibitors

Properties of beta-glucosidase produced by Aspergillus niger URM 6642 recently isolated from the Atlantic rainforest biome and its potential tolerance to saccharification of lignocellulosic biomass products and fermentation inhibitors was evaluated. The fungus was cultivated under solid state culture conditions at 37°C with different agro-industrial wastes. High levels of beta-glucosidase (3778.9 U g