Free α subunit of human chorionic gonadotrophin: molecular basis of immunologically and biologically active domains

Immunochernical studies were undertaken to identify surface-orientated epitopes of the free α subunit of human chorionic gonadotrophin (hCG-α) at the amino acid sequence level. We investigated the molecular organization of these epitopes, resolved the immunological topography in terms of spatial arrangement of antigenic domains and related structures to functions such as subunit association or receptor binding. Overlapping synthetic peptides covering the entire amino acid sequence of hCG-α, an enzymatically digested hCG-α subunit, and a reduced and alkylated hCG-α preparation were assayed in a solid-phase one-site enzyme-linked immunoassay, and in a solution-phase competitive radioimmunoassay (RIA)