Comparative studies of Iodo-bead and chloramine-T methods for the radioiodination of human alpha-fetoprotein

Human alpha-fetoprotein (h-AFP) of iodination grade was radiolabeled with Na125I by chloramine-T (conventional method) and by Iodo-bead (solid-phase method) in our laboratory under standard and varied conditions, such as quantity of h-AFP and volume of the reaction mixture. We have slightly modified the chloramine-T method and developed a protocol for the Iodo-bead method of iodination. Our results show that while the chloramine-T method yields radiolabeled h-AFP of apparently 40% higher specific radioactivity (SR) than those of the Iodo-bead method, the latter appears to be a simpler, more controllable and milder method, giving rise to a more stable population of [125I]h-AFP. This is supported by the results of radioactive counting of [125I]h-AFP collected from a Sephadex G-50 column after radioiodination, storage stability and immunoreactivity with anti-h-AFP.