An immuno-enzymatic assay of cortisol using E. coli beta-galactosidase as label.

An enzyme-assay of cortisol was established by using E. coli beta-galactosidase as a marker. The number of cortisol residues per molecule of enzyme and the method of separation of free from antibody-bound enzyme proved to be critical factors for the assessment of the assay. A sensitivity ranging from 100 to 150 pg of cortisol per tube has been achieved. A comparsion with other methods, i.e. competitive protein binding assay, radioimmunoassay and fluorimetry, is reported.