Sequence of thirteen amino acids in the C-terminal end of bovine growth hormone and localization of a disulfide bridge

Modification of arginine residues in ovine prolactin by 1,2-cyclohexanedione. Effect on binding capacity to lactogenic receptors

The reactivity of arginine residues in ovine prolactin was studied by reaction with 1,2-cyclohexanedione. Kinetic analysis of the data showed a good fit with two simultaneous pseudo-first-order equations with apparent velocity constants of 0.28 and 1.2 x 10(-2) min-1, corresponding to 1.8 'fast' and 8.7 'slow' residues, respectively. Modification led to a decrease in binding capacity to lactogenic rat liver receptors, and apparently the modification of the two 'fast' reacting arginine residues is responsible for the rapid loss of this capacity. The presence of a non-reacting arginine has been described in human and bovine growth hormones, and it is located near the carboxy-terminus. This lack of reactivity is probably due to the formation of a salt bridge, since the arginine residue becomes susceptible to modification once the peptide is separated from the rest of the molecule. This salt bridge is absent in ovine prolactin, since the homologous arginine residue is reactive with cyclohexanedione. This result suggests that there could be a difference between the three-dimensional structure of ovine prolactin and of the growth hormones, at least near the carboxy-terminal region of the molecule.

Binding characteristics of monoclonal antibodies raised against bovine growth hormone

Monoclonal antibodies have been raised against pituitary bovine growth hormone using the hybridoma procedure. The binding characteristics of the seven selected monoclonal antibodies toward the antigen molecule in its native, chemically or enzymatically treated form have been studied. The reactivities of the monoclonal antibodies with growth hormones from other species and bovine prolactin have also been investigated. The epitopes recognized by four of the produced monoclonal antibodies are conformational, whereas two other monoclonal antibodies bind to sequential determinants. Three antibodies define immunological sites located between residues 6-124 of the bovine growth hormone molecule, and one of this antibody shows higher affinity to human than bovine growth hormone. The immunoreactivity of one monoclonal antibody is enhanced by the previous binding of the antigen to polyclonal antibodies, probably because of a localized conformational change of the bovine growth hormone molecule. This antibody also shows cross-reactivity with all the homologous hormones tested, indicating to recognize a highly conserved antigenic determinant.

Specific modification of carboxyl-groups in bovine growth hormone by a soluble carbodiimide and glycinemethylester

The reactivity of the carboxyl groups in bovine growth hormone was studied by reaction with 1-ethyl-3(3-dimethylaminopropyl) carbodiimide in the presence of an excess of glycinemethylester. Localization in the molecule of the various kinetically distinguishable carboxyl groups was achieved. Highest reactivity was found in carboxyl groups 30, 125, 127 and 128. These residues were followed, as to reactivity, by a set including carboxyl groups 65, 105, 151, 152, 185 and 190. Modification of approximately one fifth of the carboxyl groups in bovine growth hormone led to an important decrease in its growth promoting activity and capacity to compete with 125I-labeled growth hormone for rat liver binding sites. Demethoxylation restored most of the original biological activity.

Immunologically active zones in bovine growth hormone

Antigenic determinant areas were detected in bovine growth hormone fragments 6--124 and 125--149, the former being predominant. Reduction and carboxymethylation of disulfide bridge 53--164 destroys the immunological reactivity of the area which is little affected by reduction and carbamoylmethylation. All the activity found in fragment 6--124 seems to be concentrated in the sequence 87--124.

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.