Preparation of biologically active radioiodinated cholecystokinin for radioreceptor assay and radioimmunoassay.

A modified method is described for the preparation of stable, high specific activity radioiodinated cholecystokinin (CCK) by its conjugation to 125I-Bolton Hunter reagent (125I-BH). Purified radioiodinated CCK (125I-BH-CCK) stimulated amylase release from isolate rat pancreatic acini with a potency identical to that of native CCK. Further, 125I-BH-CCK was highly immunoreactive and reacted with antisera directed toward both the NH2- and COOH-terminal portions of the CCK molecule. Finally, 125I-BH-CCK bound to specific receptor sites on isolated pancreatic acini.