We have found that spontaneous galactosylation of GlcNAc residues occurs in bovine colostrum, but not in dialyzed colostrum, without adding UDP-Gal as a donor substrate. UDP-Gal was shown to be present in bovine colostrum at a level ranging from 200 to 600 μM. When a tracer UDP-[14C]Gal was added to the dialyzed colostrum together with a Gal β1,4-specific β-galactosidase, remarkable incorporation of radioactivity into 24–28 kDa and 33 kDa RCA1-positive glycoproteins was demonstrated by SDS–PAGE/autoradiography. Some 100–140 kDa agalactoglycoproteins of a CHO mutant cell line were also galactosylated on a blotted membrane by the incubation in the colostrum.
