Insulin and Adrenocorticotropin Labeled With Radio-Iodine*

INTRODUCTION UNDER appropriate conditions iodine attaches itself firmly to the tyrosine groups in many proteins. The effect of this attachment upon the specific immunologic or hormonal activity of the protein appears to vary with the number (Wormall, 1930; Pressman and Sternberger, 1950) and perhaps with the position (Pressman and Sternberger, 1950) of the groups affected. A few atoms of iodine or radio-iodine per molecule of protein are quite compatible with the maintenance of immunologic reactivity in the case of anti-pneumococcus globulin, Figure 1. It has therefore seemed possible that a similar iodination, sufficient for radiotracer experimentation, may not adversely affect the activity of protein hormones The purpose of this communication is to describe observations made on insulin and ACTH METHOD OF IODINATION Essentially similar methods of iodination were used for preparations of ACTH, insulin, and gamma globulins. 10 mg. of hormone were dissolved in a few milliliters of M/15 phosphate buffer pH 7.4, placed in a cold bath