Enzyme immunoassay of progesterone at the picogram level using beta-galactosidase as label

We report here the first sensitive enzyme immunoassay of a hapten. A progesterone beta galactosidase conjugate was prepared using carbodiimide as a bifunctional reagent. Rabbit progesterone antisera were previously obtained. The separation of the bound from the free fraction of the label was performed with the help of polymerized anti rabbit gamma-globulins. The enzyme activity of the bound fraction was determined with O-nitrophenyl-beta-D-galactoside as substrate. Specificity and sensitivity (approximately 15 pg) of this enzyme immunoassay can be successfully compared with radioimmunoassay performances. It thus provides a non radioactive, inexpensive and reliable method of small molecule quantitation.