Specific antisera for the radioimmunoassay of estradiol-3-sulfate

Antisera were prepared against two types of estradiol-3-sulfate-bovine serum albumin (BSA) conjugates. The haptens were coupled to BSA through the C-6 position in the steroid molecule by the glutaraldehyde (A) or the carbodiimide method (B). In comparison the antiserum produced by method A had a high affinity for estradiol-3-sulfate (Ka = 5.64 X 10(8) M-1); that produced by method B had an even higher affinity (Ka = 2.62 X 10(9) M-1). Furthermore the latter had no significant cross-reaction with other estrogen sulfates (less than 3.83%), and no cross-reaction with other steroids (less than 0.03%). The former revealed a little cross-reactivity with some of related steroids.