Circular dichroic and immunological properties of human choriogonadotropin‐β carboxyl terminal peptides

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Abstract
Circular dichroic spectra were obtained in aqueous solution and in trifluoroethanol for several synthetic (non-glycosylated) human choriogonadotropin carboxyl terminal peptides of the .beta.-subunit ranging in size from 10 residues to 40 residues. There was no evidence for formation of .alpha.-helicity or .beta.-structure, but the spectra in 90% (vol/vol) trifluoroethanol were consistent with the occurrence of .beta.-turns. The Chou-Fasman predictive rules also suggest a high probability of .beta.-turns in these peptides which could result in the occurrence of repeating kinks. Disulfide-linked dimers were also investigated by circular dichroism, and there was evidence of stabilization of particular skewness of the disulfide dihedral angle depending upon the location of the disulfide bond. The single phenylalanyl residue at position 115 in the .beta.-subunit also contributed to the circular dichroic spectra above 250 nm. Antibodies raised to a peptide consisting of residues 111-145 contained 2 immunological determinants, but the sum of antibodies raised to separate determinant sequences do not equal those raised to the full length peptide. These data could reflect the existence of a conformation-related determinant on the 111-145 peptide or stearic hindrance of Ig binding of 2 antibodies to the same peptide.