Purification of 125I-labelled lysine-vasopressin by affinity chromatography on sepharose-bound neurophysins

Purification of 125I-labelled lysine-vasopressin has been achieved by affinity chromatography on a Sepharose 4 B conjugate of porcine neurophysins. This affinity absorbent did not retain halogenated hormone, while native lysine-vasopressin was bound on the solid support. The specific activity of purified iodinated lysine-vasopressin was 1700-1800 Ci/g, corresponding to one iodine atom per mole. By comparison with an unpurified tracer, a five times increase in the minimum detectable dose was obtained in the vasopressin radioimmunoassay.