INFLUENCE OF DIFFERENT FACTORS ON ACTIVITY AND STABILITY OF BETA-GALACTOSIDASE FROM LACTOBACILLUS-ACIDOPHILUS

Eight Lactobacillus acidophilus strains were tested for beta-galactosidase activity. The results show that beta-galactosidase is an inducible enzyme in this organism. Wide variations in enzyme properties of the strains were observed. The temperature and pH optima of the enzymes were 40-45C and 6.5-7.0, respectively. At 0.1 mM concentration, the enzyme activity in stain 4495 was slightly stimulated by 2-mercaptoethanol, partially inhibited by EDTA but remained more or less unaffected with thiomersal and ascorbic acid. In contrast, all the modulators completely inhibited the enzyme activity in strain 301. The enzyme in strain 301 was stable for 80 min at 50C, whereas the activity in strain 4495 was completely lost in 40 min. However, the enzyme was stable over a pH range of 5.8-8.0 and up to 60 days at 4 +/- 1C in both strains. The K(m) values for beta-galactosidase from both the strains were same, whereas V(max) for the enzyme from strain 301 was about 2-fold higher than that of strain 4495.