P450 monooxygenase that plays a major role in cholesterol homeostasis in the brain. Primarily catalyzes the hydroxylation (with S stereochemistry) at C-24 of cholesterol side chain, triggering cholesterol diffusion out of neurons and its further degradation (PubMed:10377398, PubMed:16505352, PubMed:28190002). By promoting constant cholesterol elimination in neurons, may activate the mevalonate pathway and coordinate the synthesis of new cholesterol and nonsterol isoprenoids involved in synaptic activity and learning (PubMed:16505352). Further hydroxylates cholesterol derivatives and hormone steroids on both the ring and side chain of these molecules, converting them into active oxysterols involved in lipid signaling and biosynthesis (By similarity). Acts as an epoxidase converting cholesta-5,24-dien-3beta-ol/desmosterol into (24S),25-epoxycholesterol, an abundant lipid ligand of nuclear NR1H2 and NR1H3 receptors shown to promote neurogenesis in developing brain (By similarity). May also catalyze the oxidative metabolism of xenobiotics, such as clotrimazole (By similarity). cholesterol + O2 + reduced [NADPH--hemoprotein reductase] = (24S)-hydroxycholesterol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] cholestanol + O2 + reduced [NADPH--hemoprotein reductase] = (24S)-hydroxycholestanol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] 7-dehydrocholesterol + O2 + reduced [NADPH--hemoprotein reductase] = cholesta-5,7-dien-3beta,24S-diol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] 7-dehydrocholesterol + O2 + reduced [NADPH--hemoprotein reductase] = cholesta-5,7-dien-3beta,25-diol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] desmosterol + O2 + reduced [NADPH--hemoprotein reductase] = (24Z),26-hydroxydesmosterol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] desmosterol + O2 + reduced [NADPH--hemoprotein reductase] = (24S)-25-epoxycholesterol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] 4beta-hydroxycholesterol + O2 + reduced [NADPH--hemoprotein reductase] = 4beta,24S-dihydroxycholesterol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] (24S)-hydroxycholesterol + O2 + reduced [NADPH--hemoprotein reductase] = (24S,25R)-24,26-dihydroxycholesterol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] (24S)-hydroxycholesterol + O2 + reduced [NADPH--hemoprotein reductase] = 24S,25-dihydroxycholesterol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] 7alpha-hydroxycholesterol + O2 + reduced [NADPH--hemoprotein reductase] = (24S)-7alpha-dihydroxycholesterol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] O2 + progesterone + reduced [NADPH--hemoprotein reductase] = 17alpha-hydroxyprogesterone + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] O2 + reduced [NADPH--hemoprotein reductase] + testosterone = 16beta,17beta-dihydroxyandrost-4-en-3-one + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] O2 + reduced [NADPH--hemoprotein reductase] + testosterone = 2-hydroxytestosterone + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] O2 + reduced [NADPH--hemoprotein reductase] + testosterone = 6beta,17beta-dihydroxyandrost-4-en-3-one + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Steroid metabolism; cholesterol degradation. Lipid metabolism; C21-steroid hormone metabolism. Expressed in high level in the pyramidal cells of the hippocampus, Purkinje cells of the cerebellum, and neuronal cell bodies in layers II/III, V, and VI of the cortex. Expressed in hippocampal and cerebellar interneurons, in retinal ganglion cells, and in a subset of retinal cells localized to the inner nuclear layer (at protein level). Mutant mice are deficient in spatial, associative and motor learning. Belongs to the cytochrome P450 family.