RADIOACTIVE LABELING OF RECOMBINANT ANTIBODY FRAGMENTS BY PHOSPHORYLATION USING HUMAN CASEIN KINASE-II AND [GAMMA-P-32]-ATP

A wide range of antibody fragments can be expressed in bacteria and de tected immunochemically via peptide tags. Using specially designed tag s, we have developed a strategy for radiolabeling antibody fragments s ecreted from bacteria. Tagged antibody fragments were secreted either into the bacterial periplasm or the culture medium. The tag was not su bject to proteolysis either in the broth or in human plasma. After aff inity purification the antibody fragments were phosphorylated with [ga mma-P-32]ATP and casein kinase II. The labeled fragments were used in a gel band-shift assay to measure antigen binding affinities. In contr ast to non site-specific methods such as radioiodination, antibodies l abeled with casein kinase II retain full immunoreactivity. Radioactive ly phosphorylated antibody fragments may have many other applications, including radioimmunoassays and radioimmunotherapy.