15hydroxylase

15-hydroxylase is not the name of a single, well-defined enzyme. It is a descriptive term for enzymes that catalyze the introduction of a hydroxyl group at the 15th carbon (C-15) of a substrate, producing a 15-hydroxylated product. In practice, 15-hydroxylase activity can be exhibited by diverse enzymes across different organisms, and the designation often refers to a functional capability rather than a specific gene.

Most commonly, 15-hydroxylation is attributed to enzymes in the cytochrome P450 superfamily, which operate as monooxygenases. These enzymes typically use molecular oxygen and electrons supplied by NADPH (via redox partners) to insert an oxygen atom into the substrate, yielding the 15-hydroxylated product and water. However, other oxygenases or flavin-containing monooxygenases can also display 15-hydroxylase activity in certain contexts.

Substrates for 15-hydroxylases are diverse and can include steroids, fatty acids, terpenoids, plant secondary metabolites, and various drugs or xenobiotics. The addition of a hydroxyl group at C-15 can influence a molecule’s solubility, reactivity, receptor binding, and subsequent metabolic fate, affecting both physiological processes and pharmacokinetics.

Physiological and pharmacological relevance varies with substrate and organism. In steroid or hormone metabolism, 15-hydroxylated products may be intermediates or catabolic end products; in pharmacology, 15-hydroxylation can modulate drug activity and clearance. Research typically involves in vitro assays with microsomes or recombinant enzymes and analytical identification of products by chromatography and mass spectrometry.

See also: cytochrome P450 enzymes, enzymatic hydroxylation, steroid metabolism.