Carboxypeptidase Digestion of Human Chorionic Gonadotropin

Abstract

Native human chorionic gonadotropin (hCG) was resistant to carboxypeptidase digestion even in the presence of urea. Isolated α subunit of the hormone (hCG-α), though unreactive to enzyme treatment in the absence of denaturant, released up to four amino acid residues from the C-terminus on incubation with a mixture of carboxy-peptidases A and B in urea. While an hCG-α product which lacked Ser-92 recombined completely with intact hCG-β, hCG-α from which Ser-92 and Lys-91 were removed showed only partial recombination. The two recombinants were devoid of any in vivo biologic activity, but retained some of the immunologic activity of the native recom-binant. These findings indicate that the integrity of the C-terminal residue of serine in hCG-α is essential for the expression of in vivo biologic activity of the native hormone.