Enzymatic Radioiodination of Gonadotropins

Abstract

A method is described for the enzymatic radioiodination of HCG, human follicle stimulating hormone (HFSH) and human luteinizing hormone (HLH) by a system consisting of lactoperoxidase, hydrogen peroxide and Na 125I. The hormones differed in their susceptibility to iodination. HCG was easily iodinated but HFSH and HLH required slightly higher concentrations of the enzyme and hydrogen peroxide. These hormones were labeled at specific activities satisfactory for radioimmunoassay. Biologic activities of these preparations were retained (HCG 108%, HFSH >62% and HLH 99%). Polyacrylamide gel electrophoresis (PAGE) of these tracers was consistent with their radiopurity. This lactoperoxidase catalyzed iodination is a gentle, simple and rapid method, and the radioiodinated preparations are suitable for radioimmunoassay.