RESUMO
The dependance of the porcine somatotropin activity on the entireness of the intrachain disulfide bridges is investigated in three biological systems: bioassay in vivo, radioimmuno assay and receptor assay with rat liver membranes. Cleavage of the disulfide bridges is accomplished by reduction, oxidation and sulfitolysis, respectively. In no case is the hormone activity completely abolished with regard to measurements in the bioassay and radioimmuno assay. In the radioligand assay with rat liver membranes neither native porcine somatotropin nor the treated hormone preparations are bound by the receptors.
Assuntos
Dissulfetos/análise , Hormônio do Crescimento/fisiologia , Aminoácidos/análise , Animais , Fenômenos Químicos , Química , Físico-Química , Focalização Isoelétrica , Oxirredução , Radioimunoensaio , SuínosRESUMO
The importance of the disulfide bridges for human somatotropin activity is investigated. The activity of somatotropin is tested by the tibia, radioimmuno-, and radioligand assays. The cleavage of disulfide bridges by sulfitolysis, reduction with dithiothreitol, or oxidation with performic acid does not completely abolish hormone activity. There is only one exception: in the radioligand assay, oxidized somatotropin is not able to displace native somatotropin from rat liver membranes. The diminution of hormone activity is independent of the charges of the groups introduced to the cysteine residues. The radioimmuno- and radioligand assays are more sensitive to conformational alterations in the somatotropin molecule than the biological test system.
