Enzyme Labeling of Steroids by the Activated Ester Method

Enzyme labeling of a steroid by the activated ester method has been investigated. The reaction of the N-hydroxysuccinimide ester of a testosterone derivative with β-D-galactosidase provided a conjugate suitable for enzyme immunoassay. Dose-response curves with satisfactory sensitivity and range of measurement could be obtained by the use of conjugates prepared at a limited molar ratio of steroid to enzyme. The activated ester method proved to be useful for enzyme labeling of antigen because of its simplicity and excellent reproducibility.