14α-demethylase

14α-demethylase is a cytochrome P450-dependent enzyme in the ergosterol biosynthesis pathway of fungi. It catalyzes removal of the 14α-methyl group from lanosterol, a necessary step in converting lanosterol to ergosterol, the main sterol component that maintains fungal cell membrane fluidity and integrity (analogous to cholesterol in human cells). Azole antifungals (e.g., fluconazole, itraconazole, voriconazole, ketoconazole, clotrimazole) inhibit this enzyme by binding to its heme iron via a nitrogen atom in their azole ring, blocking ergosterol synthesis. This leads to accumulation of toxic methylated sterol precursors and depletion of ergosterol, causing increased membrane permeability, impaired growth, and fungal cell death or growth arrest (fungistatic at lower doses, fungicidal at higher doses depending on the drug/organism). Because mammalian cells use a related but distinct demethylase for cholesterol synthesis, azoles have selective toxicity toward fungi, though ketoconazole has significant cross-reactivity with human CYP450 enzymes (including those involved in steroidogenesis), leading to side effects like gynecomastia, adrenal insufficiency, and drug interactions via CYP3A4 inhibition. Resistance to azoles can occur via mutations in the gene encoding 14α-demethylase (ERG11 gene in Candida), overexpression of efflux pumps, or upregulation of the target enzyme itself—clinically relevant in treatment failure of candidiasis and other fungal infections.