Exploring an l-arabinose isomerase from cryophile bacteria Arthrobacter psychrolactophilus B7 for d-tagatose...

A novel l-arabinose isomerase (L-AI) from Arthrobacter psychrolactophilus (Ap L-AI) was successfully cloned and characterized. The enzyme catalyzes the isomerization of d-galactose into a rare sugar d-tagatose. The recombinant Ap L-AI had an approximate molecular weight of about 258 kDa, suggesting it was an aggregate of five 58 kDa monomers and became the first record as a homo-pentamer L-AI. The catalytic efficiency (k_cat/Km) and Km for d-galactose were 0.32 mM^-1 min^-1 and 51.43 mM, respectively, while for l-arabinose, were 0.64 mM^-1 min^-1 and 23.41 mM, respectively. It had the highest activity at pH 7.0-7.5 and 60 °C in the presence of 0.250 mM Mn²⁺. Ap L-AI was discovered to be an outstanding thermostable enzyme that only lost its half-life value at 60 °C for >1000 min. These findings suggest that l-arabinose isomerase from Arthrobacter psychrolactophilus is a promising candidate for d-tagatose mass-production due to its industrially competitive temperature.