Synthesis of a tetratriacontapeptide corresponding to sequence 112–145 of the β‐subunit of hCG and production of antiserum against this synthetic peptide

A tetratriacontapeptide(P-34) corresponding to sequence 112–145 of the β-subunit of hCG(hCG-β) was synthesized by the fragment condensation method. The immunogen was prepared by coupling P-34 to bovine serum albumin by the carbodiimide or glutaraldehyde method. Antiserum was produced by injecting the immunogen into rabbits at multiple intradermal and intrasplenal sites with Freund's complete adjuvant. Eight weeks after the first immunization, antiserum was obtained that bound 30% of 125I-hCG or 125I-hCG-β at a dilution of 1:1,000. This binding was inhibited dose-dependently by hCG. In this radioimmunoassay system, the minimal detectable dose of hCG was 500 mIU/ml and, as expected theoretically, no binding to 125I-hCG-α or 125I-hLH was observed.