Characterization of a Thermally Stable β-galactosidase Produced by Thermophilic Anoxybacillus sp. AH1

Abstract

Thermostable β-galactosidases from thermophilic bacteria have attracted increasing interest to have various advantages in industrial and biotechnological applications. In this study, a highly thermally stable β-galactosidase produced by Anoxybacillus sp. AH1was purified and characterized. The highest enzyme production was achieved after the bacterium was incubated for 24 hours. The enzyme was purified by precipitation with ammonium sulphate dialysis, gel filtration chromatography using Sephadex G-75. After the purification steps, β-galactosidase was found to be purified 10.2-fold and a yield of 13.9%. The molecular mass of the galactosidase was estimated to be 75 kDa by SDS-PAGE. The purified enzyme was highly stable and retained at 71% of the original activity at 60 °C and 53% at 70 oC within 120 minutes. The Km and Vmax values of purified β-galactosidase were calculated as 1.249 mM and 0.5 μmol minutes-1, respectively. Ca2+, Zn2+, and Mg2+ significantly activated β-galactosidase activity, whereas enzyme activity was inhibited significantly by Cu+2 as well as by the metal ion chelators1,10-phenanthroline (phen) and ethylenediaminetetraacetic acid (EDTA). The Purified β-galactosidase activity was increased by PMSF (phenylmethylsulfonyl fluoride), PCMB (p-chloromercuribenzoic acid), DTT (dithiothreitol), and β-ME (β-mercaptoethanol) at 2 mM, but inhibited completely by NEM (N-ethylmaleimide) at 1 mM.