A comparison of the binding of biotin and biotinylated macromolecular ligands to an anti-biotin monoclonal antibody and to streptavidin

A competitive enzyme immunoassay was used to study the binding of biotinylated macromolecular ligands and d-biotin to an anti-biotin monoclonal antibody and to streptavidin. Solid phase BSA-c-biotin competed with biotin or biotinylated macromolecular ligands in solution for receptor binding. The concentration of d-biotin required to inhibit streptavidin binding to solid phase BSA-c-biotin by 50% was 11.5 pM. This streptavidin-biotin interaction was taken as having an affinity/avidity index of 100 and all other receptor-ligand interactions were calculated relative to this. The avidity indices calculated for streptavidin interactions with BSA-c-biotin and IgG-biotin were 17.6 and 6.6 respectively, whereas for anti-biotin the values for these ligands were 20.5 and 19.9 respectively. The interaction of anti-biotin with d-biotin had an affinity index of 0.001. Although streptavidin has the greatest binding affinity for d-biotin, its avidity for biotinylated ligands was considerably lower and comparable to that observed for anti-biotin-biotinylated macromolecule interactions.