The effects of organic solvents on the synthesis of galactose disaccharides using β-galactosidases

The use of β-galactosidases from five different sources in syntheses through transglycosylation leads to 3-O-methylallolactose, N-acetyllactosamine, N-acetylallolactosamine and Gal(β1–6)Gal. The yield and distribution of products depends on the source of the enzyme and on the reaction conditions, viz. the nature of added organic co-solvent. Yields of 3-O-methyl allolactose (47%), Gal(β1–6)Gal (6%), N-acetylallolactosamine (30%) were obtained in aqueous buffer with β-galactosidase from E. coli. The same reactions occurred at much lower rates in the presence of water-miscible organic solvents. With β-galactosidases from K. fragilis and A. oryzae, however, the synthesis of the above disaccharides occurred only in the presence of organic solvent (60% v/v triethyl phosphate, trimethyl phosphate or tetraglyme) but not in aqueous buffer solution. β-galactosidases from D. pneumoniae and B. circulans in systems incorporating organic solvent produced 3-O-methyl allolactose and N-acetyllactosamine in yields of 30–40%. The direct separation of oligosaccharides on a preparative scale can be achieved by Ca2+-ligand exchange chromatography. Ultrafiltration was also used for the efficient recycling of enzymes.