The preparation and immunological properties of 131I-labelled adrenocorticotrophin

Abstract

1. A procedure is described for preparing ¹³¹I-labelled adrenocorticotrophin suitable for use in radioimmunoassay. 2. Adsorption of labelled and unlabelled adrenocorticotrophin at low concentrations occurs to various surfaces despite the presence of diluent protein. Adsorption and desorption errors are minimized by low pH and by the use of polystyrene vials. 3. Preparations with low initial damage are obtained if the radioiodination is performed rapidly and the separation of ¹³¹I-labelled adrenocorticotrophin from unchanged [¹³¹I]iodide is carried out on cellulose columns by using dilute acid. 4. The immunological activity of ¹³¹I-labelled α^1–24-adrenocorticotrophin, but not of ¹³¹I-labelled porcine adrenocorticotrophin, decreases with increasing specific radioactivity. The involvement of tyrosine residues in the immunological specificity of the α^1–24-adrenocorticotrophin only is suggested to explain this finding.