Immobilization of the recombinant (His)6-tagged l-arabinose isomerase from Thermotoga maritima on epoxy and cupper-chelate epoxy supports

• (His)6-tagged l-arabinose isomerase was purified/immobilized on Cu-chelate Eupergit.
• The immobilized enzyme exhibited improved thermostability at 80 °C.
• The operational stability and reusability of the biocatalyst at 80 °C was low.
• Production of d-tagatose at 60 °C in repeated batch bioconversions appeared feasible.

l-Arabinose isomerase from the hyperthermophilic bacterium Thermotoga maritima (TMAI) was overexpressed in Escherichia coli as a (His)6-tagged protein and purified by heat treatment followed by immobilized Ni2+ affinity chromatography. TMAI from a heat-treated preparation was immobilized on the epoxy support Eupergit C250L (Eu) and on its copper–chelate form (Eu–Cu). The immobilization yield and the specific activity at 80 °C and pH 7.5 for the former or the latter derivatives were, respectively, 7.2 or 25 mg BSAE per gds (grams of dry solid) and 0.44 ± 0.04 or 3.1 ± 0.4 IU per gds. TMAI immobilized on Eu–Cu incubated in absence of substrate exhibited an improved thermostability compared to its soluble counterpart, the half-life time at 80 or 90 °C being not detectable for 5 h or equal to 2 h for Eu–Cu and to 1.0 h or 0.3 h for the free enzyme, respectively. However, in bioconversions in three repeated cycles at 80 °C with 18 g L−1 of initial d-galactose, the immobilized biocatalyst activity declined rapidly. At 60 °C, not only Eu–Cu derivatives used in three repeated bioconversions with initial d-galactose concentration of 18 g L−1 were stable for at least 242 h, they also yielded a d-galactose conversion and an average productivity of 29.1% and 0.06 g L−1 h−1, respectively, exhibiting better performances compared to the results at 80 °C.