The Enzymatic Synthesis and Disproportionation of Galactosyl Oligosaccharides

It was the purpose of this experiment to obtain unequivocal evidence for the suggested structures of the new oligosaccharides and to obtain evidence in support of the transgalactosylation mechanism of action of the enzyme studied. Five of the galactosyl oligosaccharides produced during the hydrolysis of lactose by an enzyme prepared from Saccharomyces fragilis have been isolated in chromatographically pure form.The three having the highest chromatographic mobilities have been shown to be 3-0-β-D-galactopyranosyl-D-glucose, 6-0-β-D-galactopyranosyl-D-glucose and 6-0-β-D-galactopyranosyl-D-galactose.The positions of the glycosidic linkages in these compounds were determined by use of the lead tetra-acetate oxidation procedure.These three disaccharides have been characterized by measurement of their optical rotations and by preparation of the crystalline phenylosazones. Evidence has been obtained in support of the following transgalactosylation mechanism of synthesis of oligosaccharides from lactose: Lactose + enzyme ⇄ galactosyl-enzyme + glucose (1) Galactosyl-enzyme + acceptor ⇄ oligosaccharide + enzyme (2) Both steps of this mechanism have been shown to be readily reversible. The cosubstrate or acceptor specificity of the enzyme was investigated.Glucosamine, sucrose, planteose and raffinose, in addition to the sugars normally found in digests of lactose and the enzyme, were found to be cosubstrates.Fructose, maltose, cellobiose and melibiose were not cosubstrates. Advisor: John H. Pazu