21-hydroxysteroid dehydrogenase (NADP+)
21-Hydroxysteroid dehydrogenase (NADP+), also known as 21-OHSD (NADP+), is an enzyme that catalyzes the reversible oxidation of various 21-hydroxysteroids utilizing NADP+ as a cofactor. This enzymatic activity is primarily involved in steroid hormone biosynthesis and metabolism, specifically in the adrenal glands and other steroidogenic tissues.
The enzyme belongs to the oxidoreductase family, more specifically those acting on CH-OH groups of donors with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is 21-hydroxysteroid:NADP+ 21-oxidoreductase.
Function
The primary function of 21-hydroxysteroid dehydrogenase (NADP+) is to catalyze the interconversion between 21-hydroxy and 21-oxo steroid derivatives. For example, it can catalyze the reduction of 21-dehydrocortisol to cortisol, using NADPH as a reducing agent. It also plays a role in the reverse reaction, oxidizing cortisol to 21-dehydrocortisol, using NADP+ as an oxidizing agent.
Role in Steroidogenesis
While 21-hydroxylase (CYP21A2) is the primary enzyme responsible for 21-hydroxylation of steroids in the adrenal glands, 21-hydroxysteroid dehydrogenase (NADP+) contributes to steroid metabolism by interconverting 21-hydroxy and 21-oxo steroids. This can influence the levels and activity of various steroid hormones, including cortisol and corticosterone.
Clinical Significance
Defects in enzymes involved in steroid hormone biosynthesis, such as CYP21A2 deficiency (congenital adrenal hyperplasia), are well-documented. However, isolated deficiencies specifically in 21-hydroxysteroid dehydrogenase (NADP+) are rare and less characterized. Any such deficiency could potentially impact steroid hormone levels and cause hormonal imbalances. However, since CYP21A2 is the primary enzyme for 21-hydroxylation, disruptions in 21-hydroxysteroid dehydrogenase (NADP+) are usually a secondary factor in steroid metabolism disorders.
Nomenclature
The enzyme is also known by other names, including:
- 21-OHSD (NADP+)
- 21-hydroxysteroid oxidoreductase (NADP+)