Overexpression and functional analysis of cold-active β-galactosidase from Arthrobacter psychrolactophilus strain F2

Cold-active β-galactosidase from Arthrobacter psychrolactophilus strain F2 was overexpressed in Escherichia coli using the Cold expression system and the recombinant enzyme, rBglAp, was characterized. The purified rBglAp exhibited similar enzymatic properties to the native enzyme, e.g., (i) it had high activity at 0 °C, (ii) its optimum temperature and pH were 10 °C and 8.0, respectively, and (iii) it was possible to rapidly inactivate the rBglAp at 50 °C in 5 min. Moreover, rBglAp was able to hydrolyze both ONPG and lactose with Km values of 2.7 and 42.1 mM, respectively, at 10 °C. One U of rBglAp could hydrolyze about 70% of the lactose in 1 ml of milk in 24 h, and the enzyme produced trisaccharide from lactose. We conclude that rBglAp is a cold-active enzyme that is extremely heat labile and has significant potential application to the food industry.