β-Subunits of equine chorionic gonadotropin and lutenizing hormone with an identical amino acid sequence have different asparagine-linked oligosaccharide chains

The glycoprotein hormones, equine chorionic gonadotropin (eCG) and lutenizing hormone (eLH), possess a β-subunit with an identical amino acid sequence. The Asn-linked oligosaccharide chains of eCGβ and eLHβ were quantitatively liberated as tritium-labeled oligosaccharides by hydrazinolysis followed by N-acetylation and NaB³H₄-reduction. Paper electrophoresis in combination with sialidase digestion and solvolytic desulfation indicated that eCGβ contained neutral and sialylated oligosaccharides, while eLHβ contained neutral, sialylated, sulfated, and both sialylated and sulfated oligosaccharides. In addition, elution profiles on a Bio-Gel P-4 column of the neutralized oligosaccharide mixtures of eCGβ and eLHβ were different, indicating that the molecular masses of oligosaccharides of the two glycoproteins are different. Therefore, this suggests that the structures of the Asn-linked oligosaccharide chains of eCGβ and eLHβ are different although they have an identical amino acid sequence.