Separation of radioiodinated angiotensins by chromatofocusing in minicolumns

Angiotensins I, II, and III (AI, AII, AIII) and Saralasin (Sar1-Ala8-AII) were labeled with 125I and separated from the nonlabeled forms on minicolumns (a Pasteur pipet ) of chromatofocusing medium. At low ionic strength, 125I-labeled angiotensins could be eluted with Polybuffer or a piperazine-histidine buffer at their approximate isoelectric points, while nonlabeled angiotensins remained adsorbed to the column and required 1 mol X liter-1 NaCl for elution. The 125I-labeled angiotensins prepared by this method were bound by antibodies (AI) and adrenal receptors (AII, Saralasin) to an extent similar to angiotensins prepared by DEAE-Sephadex A-25 chromatography. This new method of preparing radioiodinated angiotensins is rapid (15 min), inexpensive, and requires no fraction-collecting equipment.