Size Exclusion HPLC Coupled to RIA in the Study of Human Chorionic Gonadotropin (hCG) in Physiological and Pathological Conditions

Abstract

Human chorionic gonadotropin (hCG) is a glycoprotein hormone normally secreted by throphoblastic cells of the placenta during pregnancy; the peak production is attained in the latter part of the first trimester of pregnancy. During the first 4–6 weeks of pregnancy, hCG mantains the corpus luteum and stimulates steroid hormone secretion1. Similar to the pituitary gonadotropins, luteinizing hormone (LH), follicle stimulating hormone (FSH) and thyroid stimulating hormone (TSH), hCG comprises a carbohydrate part and a peptide part. The molecular mass of the complete molecule is about 40,000 Daltons. The carbohydrate moiety, comprising 30–33% of the hCG molecule, is essential for the transport and for the biologic effect of the hormone and, if removed partly or totally, the biological activity of hCG is reduced correspondingly2. hCG is composed of two dissimilar subunits: α and s linked by not covalent bonds which do not possess intrinsic biological activity3. The α-subunits of all four human glycoprotein hormones are nearly identical; they consist of 89–92 aminoacids in the same sequence but are significantly different in the carbohydrate moieties4. hCGs contains 145 aminoacids and six carbohydrate chains and differs from TSHs and FSHs but is very similar to LHs. Approximately 80% of the first 115 aminoacids of hCGs are in identical positions to those of LHs. The elucidation of the amino acids sequence of hCG revealed that hCGs possesses an extended, unique COOH-terminal glycopeptide of about 30 aminoacid residues not present in other glycoprotein hormones5.