Preparation and immunoreactive properties of monoiodinated angiotensin labelled at high specific activity

Monoiodinated angiotensin II at a specific activity in the order of 1 C/mg can be prepared with high yields by controlling the pH of iodination and can be purified on G-25 Sephadex. The fractions from the head to the centre of the single peak of radioactivity obtained by gel filtration of the iodination mixture contain pure monoiodinated angiotensin. The monoiodinated derivative shows an immunoreactivity very close to that of the native hormone; in contrast, the diiodinated derivative has a low immunoreactivity and its use as a tracer results in a loss of sensitivity in the radioimmunoassay of angiotensin II. It is suggested that the use of the monoiodinated derivative in pure form should be recommended whenever a small hormonal polypeptide labelled at high specific activity is to be prepared for radioimmunoassay purposes.