Purification and properties of β-D-galactosidase from Bifidobacterium bifidum exhibiting a transgalactosylation reaction

β-D-Galactosidase was extracted by ultrasonic treatment in the presence of Triton X-100. The transgalactosylase (TGase) was separated from other β-D-galactosidases and purified 1720-fold, as measured by the TGase assay. The enzyme was shown to be homogeneous on native PAGE. The complex nature of the enzyme was demonstrated by SDS/PAGE, with four major protein bands of 163, 170, 178 and 190 kDa. The molecular mass was estimated to be 362 kDa by gel chromatography, and the pI was 5.25. The purified enzyme was stable at temperatures below 45 o C and over the pH range from 6.5-8. Lactose hydrolysis by the purified enzyme and by Bifidobacterium bifidum cells took place at the same pH and temperature, at pH 6.5 and 37 o C respectively