A new homogeneous enzyme immunoassay using recombinant enzyme fragments

Homogeneous enzyme immunoassays have played a major role in the development of simple and easy to use diagnostic tests for clinical laboratory instrumentation. A novel homogeneous enzyme immunoassay system, CEDIA, has been developed using enzyme fragments prepared by recombinant DNA technology. Two separate genes are engineered to express two separate polypeptide fragments: enzyme-donor (ED) and enzyme-acceptor (EA). These fragments can spontaneously recombine to form active beta-galactosidase enzyme. Ligands can be attached to the ED peptide in such a way that the degree of recombination is controlled by the binding of anti-ligand antibodies to the enzyme donor-ligand conjugate. CEDIA methodology is based on the competition between ligand in the sample and ED-ligand conjugate for limiting the amount of antibody binding sites. The advantages of the CEDIA immunoassay system over conventional homogeneous EIA's include a linear dose response curve and lower limits of detection of analytes in human body fluids. The demonstrated sensitivity achievable with CEDIA technology suggests further applications on a wide range of analytes including vitamins, hormones, drugs and cancer markers. A new variant of CEDIA technology leading to a single liquid reagent immunoassay useful for on-site testing has also been developed.