ISOLATION AND SOME PROPERTIES OF THE THERMOSTABLE β-GALACTOSIDASE OF PYROCOCCUS WOESEI EXPRESSED IN ESCHERICHIA COLI

The enzyme with β-galactosidase activity from E. coli BL21(DE3) transformant containing the gene encoding enzyme from Pyrococcus woesei (DSM 3773) was isolated using cell extraction in 0.01 M phosphate buffer (pH 7.2), protein thermopredpitation at 85C, precipitation at acetone/extract ratio of 1:1 (v/v) and gel filtration on Sephadex G-200. The increase in the enzyme specific activity was determined using ONPG as substrate. The activity increased from 2.9 × 10³ U/mg protein to 37 × 10³ U/mg. Thermoprecipitation removed 78% of E. coli protein and retained 92% of the cell extract activity. The acetone precipitation and gel filtration applied in the next purification steps led to homogeneous enzyme with specific activity of 37,700 U/mg protein. The isolated enzyme had a half-life of 23 h and 9 h during incubation at 85C and 100C, respectively, in 0.1 M citrate-phosphate buffer (pH 5.4).