Preparation and characterization of an improved beta-COOH-terminal immunogen for generation of specific and sensitive antisera to human chorionic gonadotropin.

Abstract

Antisera raised against the entire β-subunit of hCG usually cross-react to some extent with human LH. While this degree of cross-reaction in serum assays can be relatively minor, human LH becomes a greater source of error when urine specimens are concentrated for measurement of very low levels of hCG secretion. To circumvent this problem, peptides from the unique β-COOH-terminal region can be employed as immunogens to elicit antisera of greater specificity for hCG, but, to date, the synthetic and desialylated peptides from this region have failed to produce antibodies with sufficient affinities for clinical application. Since the presence of sialic acid on these peptides could influence their conformation in native hCG, we have undertaken to study the immunochemistry of sialic acid-containing βCOOH-terminal peptides. These peptides were produced by tryptic digestion of the β-subunit and separated from the disulfide-rich core by gel filtration. After reduction and carboxymethylation to destroy any contamin...