Biosynthesis of 6-β-galactinol by β-galactosidase from rat mammary gland and E. coli

The synthesis of 6-β-galactinol by rat mammary gland extracts in vitro, was shown to be catalyzed by β-galactosidase (EC 3.2.1.23) by transferring the galactosyl group of lactose (K m = 37 mM) to myo-inositol (K m = 380 mM) with a pH optimum of 3.6. Highly purified commercial β-galactosidase from E. coli catalyzed a similar reaction yielding 6-β-galactinol from lactose (K m = 20 mM) and myo-inositol (K m = 770 mM) at a pH optimum of 7.2. The identity of 6-β-galactinol synthesized by the action of β-galactosidase from either source was verified by gas chromatography and mass spectrometry of the fully trimethylsilylated disaccharide.