SERUM HCGβ-CORE FRAGMENT IS MASKED BY ASSOCIATED MACROMOLECULES

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Abstract
To determine if .beta.-core fragment is present in serum from individuals with pregnancy and choriocarcinoma, samples were analyzed by gel filtration and fractions assessed by immunoassays (Mr = 15,000). In agreement with published reports, only minute amounts of .beta.-core fragment were detected (< 0.1% of hCG level). A small amount of .beta.-core fragment activity was identified near the void volume of the column (Mr > 60,000). This high molecular weight material was pooled and dissociated with 3M ammonium thiocyanate, and gel filtration repeated. A much more significant .beta.-core fragment peak was then detected (Mr = 15,000). After dissociation, .beta.-core fragment was 18% (mol/mol) of the hCG level in early pregnancy serum, 91% in mid-pregnancy serum, 50% in term pregnancy serum, but only 1.3% in choriocarcinoma serum, pre-therapy. We conclude that the major form of .beta.-core fragment found in serum is associated with other macromolecules, which mask the .beta.-core fragment epitope to existing hCG.beta. antibodies. Measurements made on the dissociated .beta.-core fragment complex are much more in keeping with pregnancy levels found in urine.

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