Lactobacillus bifidusの代謝に関する研究-3-L.bifidusのβ-ガラクトシダーゼの精製とその性状について

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β-Galactosidase was extracted from cells of L. bifidus A-3 by ultrasonic oscillation. The enzyme extracted was purified about 34-times by ammonium sulfate fractionation, DEAE-cellulose column chromatography and Sephadex G-200 gel filtration, and the purified enzyme was found to be almost homogeneous by polyacrylamide gel discelectrophoresis. The purified enzyme had an optimum pH at 7.0 and an optimum temperature at 50°C for the reaction in phosphate buffer, and was stable at pH values from 6.0 to 7.0 at 5°C, but was inactivated below pH 4.0 and above 60°C. The enzyme was activated by divalent metal ions such as Mn2+ and Fe2+, and reagents containing sulfhydryl group, whereas was markedly inactivated by Cu2+, Hg2+ and EDTA. Lactose and lactulose were hydrolyzed by the purified β-galactosidase from L. bifidus A-3. Lacto-N-tetraose of human milk oligosaccharide was split by the enzyme, and liberation of galactose and production of lacto-N-triose II with the cleavage of its β-(1→3)-galactosidic linkage were observed. However no detection of glucose in enzymatic breakdown products shows that β-(1→4)-galactosidic linkage of lacto-N-tetraose is not attacked at all. Di-N-acetylneuraminyl-lacto-N-fucononaose could not be attacked entirely by the enzyme.
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