Abstrait

Free and immobilized thermophilic alpha-L-arabinofuranosidase for arabinose production

Giuseppe Squillaci, Alessandra Esposito, Francesco La Cara, Alessandra Morana*

In the present study, the immobilization in calcium alginate beads of the alpha-L-arabinofuranosidase from the extremophilic Archaeon Sulfolobus solfataricus expressed in Escherichia coli was described. The biochemical properties and the capability to release L-arabinose from L-arabinose-containing substrates were investigated as well.
Since the recombinant activity was localized in the cytosol and in the cell membranes, alginate beads entrapping E. coli whole cells were also prepared. The immobilization was carried out by mixing the enzyme and the cells with 3% (w/v) sodium alginate, and then adding 0.15 mol/L CaCl2. The immobilization yield was high, with 100% and 98% of recovery for the enzyme and the cells, respectively. The optimal pH was shifted to a lower value and the thermophilicity was increased, reaching 85°C for the enzyme and 95°C for the cells. The immobilized preparations showed enhanced thermal stability with half-lives of 16 h and 20 h at 90°C for the enzyme and the cells, respectively. The efficiency of the alpha-L-arabinofuranosidase in producing L-arabinose was tested by using L-arabinose-containing substrates. The enzyme was not active toward polymeric substrates such as arabinan and debranched arabinan, whereas 1,5-alpha-L-arabinooligosaccharides were hydrolysed giving 68% of L-arabinose after 24 h of incubation at 80°C with the immobilized enzyme.