Enzymatic conversion of d-galactose to d-tagatose: Cloning, overexpression and characterization of l-arabinose isomerase from Pediococcus pentosaceus PC-5.

The gene encoding l-arabinose isomerase from food-grade strain Pediococcus pentosaceus PC-5 was cloned and overexpressed in Escherichia coli. The recombinant protein was purified and characterized. It was optimally active at 50°C and pH 6.0. Furthermore, this enzyme exhibited a weak requirement for metallic ions for its maximal activity evaluated at 0.6mM Mn2+ or 0.8mM Co2+. Interestingly, this enzyme was distinguished from other l-AIs, it could not use l-arabinose as its substrate. In addition, a three-dimensional structure of l-AI was built by homology modeling and l-arabinose and d-galactose were docked into the active site pocket of PPAI model to explain the interaction between l-AI and its substrate. The purified P. pentosaceus PC-5 l-AI converted d-galactose into d-tagatose with a high conversion rate of 52% after 24h at 50°C, suggesting its excellent potential in d-tagatose production. [ABSTRACT FROM AUTHOR]