Galactosyltransferases in Human Submaxillary Glands and Stomach Mucosa Associated with the Biosynthesis of Blood Group B Specific Glycoproteins

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Abstract
The immunodominant group of the blood group B determinant is a terminal non‐reducing α‐D‐galactosyl residue; however β‐D‐galactosyl residues are present in B‐active glycoproteins within the interior of the carbohydrate chains and some incomplete chains probably end with terminal non‐reducing β‐D‐galactosyl units. Partially fractionated homogenates of human gastric mucosa and submaxillary glands were used to detect and characterise the α‐ and β‐galactosyltransferases involved in the transfer of D‐galactose to endogenous, as well as exogenous, macromolecular acceptors.α‐D‐Galactosyltransferases were demonstrated in tissues from blood group B and AB donors that transferred D‐galactose in α‐linkage to H‐active glycoproteins. This activity was not detectable in tissues from group A or O donors. The enzymes were membrane‐bound but partial solubilisation was achieved with Triton X‐100 or digitonin. The products of galactosyl transfer were characterised by precipitation with immunological reagents, β‐D‐Galactosyltransferases that used H‐active glycoproteins as acceptors were detected in tissue preparations from donors of all ABO blood groups.The transferases were activated by Mn2+ ions and incorporation of D‐galactose into endogeneous B‐substance was stimulated by uridine diphosphate N‐acetylglucosamine and guanosine diphosphate L‐fucose.