Sialic Acids, but Not Their Linkage to Galactose Residues, Are Required for Full Expression of the Biological Activity of Human Chorionic Gonadotropin

One of the characteristic features of the asparagine-linked sugar chains of human chorionic gonadotropin (hCG) is that their sialic acid residues occur exclusively as the Neu5Acα2→ 3Gal group. In order to determine whether this sialic acid linkage is important for the functional role played by the sugar moiety of hCG or not, isomeric hCG containing the Neu5Acα2→6Gal group was prepared and its hormonal activity in vitro was investigated. On addition of the isomeric hCG to the culture medium of a murine Leydig tumor cell line, it was found that it shows the same hormonal activity as natural hCG.