Hydroxysteroid dehydrogenase

Hydroxysteroid Dehydrogenase

Diagram of steroidogenesis, showing the role of hydroxysteroid dehydrogenases.

Hydroxysteroid dehydrogenases (HSDs) are a group of enzymes that play a crucial role in the metabolism of steroids. These enzymes are involved in the interconversion of active and inactive forms of steroid hormones, thus regulating their biological activity.

Function

Hydroxysteroid dehydrogenases catalyze the oxidation and reduction of hydroxysteroids. They are responsible for the conversion of ketones to alcohols and vice versa in steroid molecules. This activity is essential for the biosynthesis and metabolism of steroid hormones such as testosterone, estrogen, and cortisol.

Types of Hydroxysteroid Dehydrogenases

There are several types of hydroxysteroid dehydrogenases, each with specific functions and substrate specificities:

• 3_-Hydroxysteroid dehydrogenase (3_-HSD): Converts _5-steroids to _4-ketosteroids, a critical step in the biosynthesis of all classes of hormonal steroids.
• 11_-Hydroxysteroid dehydrogenase (11_-HSD): Exists in two isoforms, 11_-HSD1 and 11_-HSD2, which regulate the conversion of active cortisol to inactive cortisone and vice versa.
• 17_-Hydroxysteroid dehydrogenase (17_-HSD): Involved in the conversion of androstenedione to testosterone and estrone to estradiol.

Role in Steroidogenesis

Hydroxysteroid dehydrogenases are integral to the process of steroidogenesis, the production of steroid hormones from cholesterol. They ensure the proper balance and function of steroid hormones by regulating their activation and inactivation.

Clinical Significance

Dysfunction or abnormal expression of hydroxysteroid dehydrogenases can lead to various disorders. For example, mutations in 11_-HSD2 can cause apparent mineralocorticoid excess, leading to hypertension. Similarly, defects in 17_-HSD can result in disorders of sexual development.

Related Pages

• Steroid hormone
• Enzyme
• Metabolism
• Endocrinology