Incorporation of Galactose into Blood‐Groups (ABH) Precursor Substance by Lactose Synthetase from Human Milk

It has been shown that an enzyme preparation from human milk having lactose synthetase activity is capable of incorporating galactose residues into water‐soluble blood‐group substance. A suitable acceptor substance for investigating the enzymatic galactose transfer was obtained from blood‐group H‐substance by sequential removal of fucose and terminal galactose residues. When galactose was incorporated into this acceptor substance with the help of a preparation of galactosyl transferase from human milk in the presence of UDP‐galactose, a remarkable increase in cross‐reactivity with anti‐type‐14 pneumococcus sera could be observed. Since a glycoprotein with “type‐14 specificity”, having galactose as the serologically determinant group, is the precursor of the water‐soluble blood‐group A, B, H and Le substances, this enzymatic galactose transfer would appear to be an essential step in the biosynthesis of the blood‐group‐active compounds. Evidence for the identity of the enzyme responsible for the synthesis of type‐14‐specific sites with lactose synthetase of human milk was obtained from competition experiments.