Figure 6.

Principles of the cloned enzyme donor immunoassay. (A) In the absence of free drug, formation of a complete tetrameric enzyme is inhibited, and no coloured product is generated after addition of substrate to the reaction mixture. (B) In presence of free drug, it competes with the enzyme donor (ED)-drug conjugate for anti-drug antibody binding sites. Complete active enzyme molecules are formed, which converts the colourless substrate into coloured product in proportional to the drug concentration. EA, enzyme acceptor.