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Sucrose synthases (SuSys) have been attracting great interest in recent years in industrial biocatalysis. They can be used for the cost-effective production of uridine 5'-diphosphate glucose (UDP-glucose) or its in situ recycling if coupled to glycosyltransferases on the production of glycosides in the food, pharmaceutical, nutraceutical, and cosmetic industry. In this study, the homotetrameric SuSy from Acidithiobacillus caldus (SuSyAc) was immobilized-stabilized on agarose beads activated with either (i) glyoxyl groups, (ii) cyanogen bromide groups, or (iii) heterogeneously activated with both glyoxyl and positively charged amino groups. The multipoint covalent immobilization of SuSyAc on glyoxyl agarose at pH 10.0 under optimized conditions provided a significant stabilization factor at reaction conditions (pH 5.0 and 45 °C). However, this strategy did not stabilize the enzyme quaternary structure. Thus, a post-immobilization technique using functionalized polymers, such as polyethyleneimine (PEI) and dextran-aldehyde (dexCHO), was applied to cross-link all enzyme subunits. The coating of the optimal SuSyAc immobilized glyoxyl agarose with a bilayer of 25 kDa PEI and 25 kDa dexCHO completely stabilized the quaternary structure of the enzyme. Accordingly, the combination of immobilization and post-immobilization techniques led to a biocatalyst 340-fold more stable than the non-cross-linked biocatalyst, preserving 60% of its initial activity. This biocatalyst produced 256 mM of UDP-glucose in a single batch, accumulating 1 M after five reaction cycles. Therefore, this immobilized enzyme can be of great interest as a biocatalyst to synthesize UDP-glucose.

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Differently activated agarose-based supports were evaluated for co-immobilization of a crude extract from Penicillium janczewskii containing xylanase, β-xylosidase and α-Larabinofuranosidase activities. Adequately selecting support and immobilization conditions (8 h, using agarose with 10% crosslinking) increased enzyme levels substantially, mainly in relation to the xylanase (2-fold). A coating with dextran aldehyde MW 6,000 Da, partially oxidized, covalently attached the enzymes to the support. Optimum activity was verified in the pH range 2-4, and at 50, 65 and 80 °C for the xylanase, α-L-arabinofuranosidase and β-xylosidase, 2 respectively. The xylanase was highly thermostable retaining more than 70% of activity even after 24 h incubation at 60 and 70 °C; and at 80 °C its half-life was 1.7 h. The half-lives of the β-xylosidase and α-L-arabinofuranosidase at 50 °C were 2.3 and 3.8 h, respectively. The coimmobilization of the enzymes on a single support give raise to a functional multi-enzymatic biocatalyst acting in the complete hydrolysis of different and complex substrates such as oat spelt and wheat arabinoxylans, with xylose yield higher than 40%. The xylanase and the α-Larabinofuranosidase presented high stability retaining 86.6 and 88.0% of activity after 10 reuse cycles.

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