XYLOSE - THE FIRST AMBIDENT ACCEPTOR SUBSTRATE FOR GALACTOSYLTRANSFERASE FROM BOVINE-MILK

In the past few years the acceptor substrate specificity of beta 1,4-g alactosyltransferase (GalT) from bovine milk has been investigated ext ensively by various groups. In each case, the beta 1,4-galactosylated products have been observed exclusively. Recently we reported on a fra me-shifted recognition of modified acceptor substrates resulting in th e formation of beta,beta-trehalose type disaccharides. In an extension to these investigations we have now found that xylose is recognized b y the enzyme both in the normal and in the reverse orientation. Theref ore galactosylation of xylose results in a mixture of beta 1,4- and be ta 1,beta 1-galactopyranosyl xylopyranosides. Synthesis and preparatio n of both disaccharides and their behavior toward beta-galactosidase f rom E. coli are described. The results lead to some implications about the active site of GalT.