Beta-D-galactosidase from Enterobacter cloacae: production and some physicochemical properties

A bacterial strain isolated from soil and identified as Enterobacter cloacae had been found to be capable of producing both intra and extracellular beta-D: -galactosidase.The intracellular enzyme was thermostable and its optimum temperature, pH and time for enzyme-substrate reaction were found to be 50 degrees C, 9.0 and 5 min respectively, using ONPG as substrate. The maximum beta-galactosidase production in shake flask was achieved at 30 degrees C, pH 7.0, incubation time 72 h using 50 ml medium in 250 ml Erlenmeyer flask. Only Mg(2+) 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 degrees 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 beta-galactosidase using ONPG as substrate at 50 degrees C were 2.805 mM and 37.45 x 10(-3) mM/min/mg, respectively.