β-d-Galactosidase from Enterobacter cloacae: Production and Some Physicochemical Properties

Abstract

A bacterial strain isolated from soil and identified as Enterobacter cloacae had been found to be capable of producing both intra and extracellular β-d-galactosidase.The intracellular enzyme was thermostable and its optimum temperature, pH and time for enzyme—substrate reaction were found to be 50 °C, 9.0 and 5 min respectively, using ONPG as substrate. The maximum β-galactosidase production in shake flask was achieved at 30 °C, pH 7.0, incubation time 72 h using 50 ml medium in 250 ml Erlenmeyer flask. Only Mg²⁺ stimulated the activity of enzyme. Cetyl trimethyl ammonium bromide showed stimulatory effect on catalytic activity of the enzyme whereas EDTA inhibited enzyme activity. The enzyme retained its activity upto 55 °C after incubating at that temperature for 1 h.The maximum activity of crude intracellular enzyme was 14.35 IU/mg of protein. The K _m and V _max values of β-galactosidase using ONPG as substrate at 50 °C were 2.805 mM and 37.45 × 10⁻³ mM/min/mg, respectively.