Subunits of human chorionic gonadotropin and their radioimmunoassays.

HCG subunits were isolated from hCG by chromatography on DEAE Sephadex A-50. Iodination of hCG by the enzymatic iodination method resulted in a preparation labeled almost exclusively on the α-subunits of hCG, and masking of tyrosine residues in the β-portion when bound to the α-portion of hCG molecule was interpreted.Antisera of the hCG subunits enabled radioimmunoassay of those subunits. Sera obtained from pregnant women were radioimmunoassayed for hCG, hCG-α and hCG-β in respective homologous radioimmunoassay systems. Real amounts of those hormones were calculated by subtracting the interferes of non-homologous hormones in the homologous assays. Absolute amounts of hCG reached its peak (several microgrammes per ml) in the first trimester, then decreased and continued the values less than 1.5 microgrammes per ml thereafter. Surprisingly the amounts of hCG-α in sera increased in the former half, reaching several hundreds nanogrammes per ml in the latter half of pregnancy, while the amounts of hCG-β were ranged in less than 100 nanogrammes per ml. The significance of immunoreactive hCG-α during pregnancy was speculated.