A new homogeneous enzyme immunoassay. Its application to measurement of alpha-fetoprotein

A rapid and sensitive homogeneous enzyme immunoassay (homogeneous EIA) was developed for determination of serum proteins such as alpha-fetoprotein (AFP). There are two assay systems, one is a competitive system including horseradish peroxidase (HRP)-labeled antigen, antibody and substrate, and the other is a non-competitive system including HRP-labeled antibody and substrate. When the aggregate was formed through the binding of HRP-labeled AFP and anti-AFP antibody or through the binding of HRP-labeled anti-AFP antibody and AFP, HRP of the aggregates, as compared with HRP of free conjugates, exhibited marked activity in the presence of 35 mM H2O2. The extent of stimulation of HRP activity depended on the amount of AFP. This new assay method is very simple and sensitive, and can be used for the determination of any kind of protein, hormone, or drug.