Equine testicular aromatase: Substrates specificity and kinetic characteristics

Abstract

1. 1. In the stallion, estrogens were synthesized and sulfated in vivo by the testis. 2. 2. The equine testicular enzyme aromatized androgens and 19-norandrogens with similar velocity, but not 16α-hydroxytestosterone or epitestosterone in contrast to the human placental aromatase. 3. 3. One single enzyme was implicated in the aromatization of androstenedione, testosterone, 19-norandrostenedione and 19-nortestosterone by ETMES. 4. 4. During the process of androstenedione aromatization by ETMES, 19-hydroxyandrostenedione and 19-oxoandrostenedione were released and 4-hydroxyandrostenedione was a competitive inhibitor causing an additional irreversible enzyme inactivation which is what occurs with HPMES. 5. 5. Dihydrotestosterone was a potent competitive inhibitor of aromatase activity. © 1991.