36] Radiolabeling of human leukocyte and immune interferons with 125I and lactoperoxidase

Abstract

This chapter focuses on the radiolabeling of human leukocyte and immune interferons with 125I and lactoperoxidase. The advent of purified natural and recombinant interferons (IFNs) has made it possible to develop radio-immune assays for them and to carry out structural and functional studies, which are otherwise not feasible. IFNs radiolabeled with 125I are used for radio-immune assays and studies on cell receptors for IFNs. The procedures most commonly employed for radioiodination of proteins make use of chloramine T, lactoperoxidase, or Bolton–Hunter reagent. There are other procedures as well. The choice of the procedure may depend on factors, such as the desired specific radioactivity of the labeled product, chemical and biological stability of the sample under the radiolabeling procedure, and the relative cost of the procedure. The chloramine T procedure has been used extensively for the radioiodination of polypeptides, such as hormones, to high specific activities. Chloramine T and lactoperoxidase procedures catalyze the iodination mostly at tyrosine residues in proteins being labeled, whereas with Bolton–Hunter reagent, a radioiodinated phenyl group, is transferred to free amino groups of the protein.