Detection of immunologically active zones in equine growth hormone

Peptide fragments, obtained from equine growth hormone by cyanogen bromide cleavage and further chemical treatment, were isolated and identified. Their immunological reactivities were tested by hemagglutination and complement fixation methods using rabbit antisera against native hormone. Antigenic determinants were detected in the fragments comprising amino acid sequences 5-72 and 73-123, this last one being predominant. Fragment 124-178 had very low reactivity. Nitration of peptide 73-123 did not modify its immunological properties,but oxidation diminished them. Comparison of the antigenicity of equine growth hormone fragment 73-123 with that of the homologous ovine growth hormone fragment 86-123 lent support to the hypothesis that at least one antigenic determinant area in the horse hormone fragment is dependent on sequence 86-123.