Enzymatic Labeling of Proteins with ¹²⁵I

Abstract

A major disadvantage of the earlier protein iodination procedures lies in the use of some harsh chemicals which can introduce unwanted and irreversible changes in the structure of the labeled preparations. To circumvent this, iodination by peroxidase enzyme-containing or peroxide generating systems was applied by numerous authors since the first short report on the feasibility of this by Keston (1944), It has been used for Immunoglobulin labeling by Marchalonis (1969) using lactoperoxidase, hydrogen peroxide, and iodide. The procedure described here in Part A is based on this procedure. Part B describes the procedure used by Dr. Ah-kau Ng (NIH, National Cancer Institute, Bethesda, MD) to iodinate exposed proteins on human tumor cell surfaces, based on the publication of Phillips and Morrison (1971).