Equine testicular aromatase: substrates specificity and kinetic characteristics.
1. In the stallion, estrogens were synthesized and sulfated in vivo by the testis. 2. The equine testicular enzyme aromatized androgens and 19-norandrogens with similar velocity, but not 16 alpha-hydroxytestosterone or epitestosterone in contrast to the human placental aromatase. 3. One single enzyme was implicated in the aromatization of androstenedione, testosterone, 19-norandrostenedione and 19-nortestosterone by ETMES. 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. Dihydrotestosterone was a potent competitive inhibitor of aromatase activity.
Gaillard
J L
JL
Laboratorie de Biochimie, URA Centre National de la Recherche Scientifique, Université, Caen, France.
D000728:Androgens; D000818:Animals; D001141:Aromatase / Q000378:metabolism*; D047072:Aromatase Inhibitors; D013196:Dihydrotestosterone / Q000494:pharmacology; D006736:Horses; D066298:In Vitro Techniques; D008297:Male; D008861:Microsomes / Q000201:enzymology; D013379:Substrate Specificity; D013737:Testis / Q000201:enzymology*
D000728:Androgens; D047072:Aromatase Inhibitors; D013196:Dihydrotestosterone; D001141:Aromatase