High Specific Activity Labeling of Protein with I131 by the Iodine Monochloride Method.

SummaryA modified iodine monochloride method suitable for preparing I131-labeled proteins of a high degree of radioactivity is described, and results are given. Hydrogen peroxide present in high level I131 preparations is destroyed with catalase. Then IC1 is added to a mixture of the I131 as iodide and the protein to be iodinated. Total iodine content of I131 preparations sets a limit on the specific activity of I131-labeled proteins that can be achieved with a low degree of iodination. In the two commonly used methods for producing I131 (fission of U235 and thermal neutron irradiation of natural tellurium) stable I127 and long-lived I129 are also formed. Analysis showed the total iodine content of fission product I131, as received from Oak Ridge National Laboratory soon after processing, to average 2.4 μg per 100 mc, 3 times the amount present as I131 (0.8 μg/100 mc). For I131 produced from tellurium it was substantially greater. Since the ratio of total iodine to I131 increases with time after processin...