Molecular forms of human chorionic gonadotropin in serum, urine, and placental extracts.

The molecular forms of human chorionic gonadotropin (hCG) were assessed in serum, urine, and placental extracts by gel filtration chromatography using radioimmunoassays for hCG, hCGalpha, and hCGbeta and a radioreceptor assay for hCG. The predominant form in all three biologic specimens was native-sized hCG. An excess of free alpha-subunit was also found in all three specimens. A small molecular weight fragment, reactive in the hCGbeta assay, was noted in urine and placental extracts. A large molecular form, reactive in all three radioimmunoassays and in the radioreceptor assay, was found in placental extracts. This large molecular species could not be dissociated by conditions that totally dissociate hCG.