Biochemical mechanism of aromatization

Area of Science:

• Biochemistry
• Endocrinology
• Organic Chemistry

Background:

• Placental aromatase is crucial for converting androgens to estrogens.
• The enzymatic mechanism of this aromatization is not fully elucidated.
• Understanding this pathway is key to reproductive physiology.

Purpose of the Study:

• To elucidate the sequential hydroxylation mechanism of androgen aromatization by placental aromatase.
• To identify the site of the rate-determining hydroxylation step.
• To investigate the implications of the reaction mechanism on product feedback inhibition.

Main Methods:

• Chemical and biochemical analyses were employed.
• Immunological evidence was used to support the proposed mechanism.
• Kinetic studies likely informed the identification of the rate-determining step.

Main Results:

• Aromatization involves three sequential hydroxylations.
• The first two hydroxylations occur at the C-19-methyl group.
• The final, rate-determining hydroxylation occurs at the 2 beta position.
• The reaction product rapidly collapses to estrogen nonenzymatically.
• Absence of direct enzyme-product relationship prevents feedback inhibition.

Conclusions:

• A detailed mechanism for estrogen formation by placental aromatase is proposed.
• The 2 beta hydroxylation is the critical, rate-limiting step.
• The nonenzymatic collapse and lack of feedback inhibition have significant physiological implications.