[53] A radioimmunoassay for chicken avidin

This chapter presents an overview of a radioimmunoassay for chicken avidin. There are a number of assay methods for avidin. Most of these are based on the specific biotin binding property of avidin but are hampered by the variable concentrations of endogenous tissue biotin. In addition, unknown biotin-binding factors of the tissue may affect results. Avidin radioimmunoassay (RIA) is based on the competition of 125I-labeled and unlabeled avidin to the same binding site of the antibody. The bound and free avidin are then separated with a second antibody bound to solid matrix and centrifuged. Radioactivity of the pellet is counted in a gamma counter.