Equine testicular aromatase: substrates specificity and kinetic characteristics.

The research investigates the substrates specificity and kinetic characteristics of equine testicular aromatase, a key enzyme involved in the synthesis of estrogens in male horses. Key findings revealed the enzyme’s ability to aromatize androgens and ability of certain compounds to inhibit its activities.

Overview of Equine Testicular Aromatase Functionality

• This research examines the role and functioning of the equine testicular aromatase enzyme in male horses, where it’s involved in producing estrogens synthesized and sulfated in the testis.
• Evidence shows the testicular enzyme produces aromatic compounds from androgens and 19-norandrogens at similar rates. This is unlike the human placental aromatase which can also process 16 alpha-hydroxytestosterone or epitestosterone.

Substrate Specificity and Aromatization Process

• The study reports the same single enzyme being responsible for the aromatization of numerous substrates, including androstenedione, testosterone, 19-norandrostenedione and 19-nortestosterone.
• In the process of aromatizing androstenedione, two compounds, namely 19-hydroxyandrostenedione and 19-oxoandrostenedione, were released.
• Additionally, there is a competitive inhibition by 4-hydroxyandrostenedione that results in irreversible enzyme inactivation, similar to what happens with HPMES.

The Role of Dihydrotestosterone

• The study reveals that dihydrotestosterone, another steroid hormone, acts as a potent competitive inhibitor of aromatase activity. This introduces another layer of regulation to the steroidogenesis process in male horses.

Significance of the Findings

• These findings increase the understanding of the role and functioning of aromatase in the synthesis of estrogens in male horses and shed light on regulatory mechanisms that control the enzyme’s activity.
• The comparison with human placental aromatase also provides valuable insights into the diversity and specificity of enzyme functioning across different species.