A cytochrome P450 monooxygenase that catalyzes the conversion of C19 androgens, androst-4-ene-3,17-dione (androstenedione) and testosterone to the C18 estrogens, estrone and estradiol, respectively (PubMed:27702664, PubMed:2848247). Catalyzes three successive oxidations of C19 androgens: two conventional oxidations at C19 yielding 19-hydroxy and 19-oxo/19-aldehyde derivatives, followed by a third oxidative aromatization step that involves C1-beta hydrogen abstraction combined with cleavage of the C10-C19 bond to yield a phenolic A ring and formic acid (PubMed:20385561). Alternatively, the third oxidative reaction yields a 19-norsteroid and formic acid. Converts dihydrotestosterone to delta1,10-dehydro 19-nordihydrotestosterone and may play a role in homeostasis of this potent androgen (PubMed:22773874). Also displays 2-hydroxylase activity toward estrone (PubMed:22773874). Mechanistically, uses molecular oxygen inserting one oxygen atom into a substrate, and reducing the second into a water molecule, with two electrons provided by NADPH via cytochrome P450 reductase (CPR; NADPH-ferrihemoprotein reductase) (PubMed:20385561, PubMed:22773874). 3 O2 + 3 reduced [NADPH--hemoprotein reductase] + testosterone = 17beta-estradiol + formate + 4 H(+) + 4 H2O + 3 oxidized [NADPH--hemoprotein reductase] androst-4-ene-3,17-dione + 3 O2 + 3 reduced [NADPH--hemoprotein reductase] = estrone + formate + 4 H(+) + 4 H2O + 3 oxidized [NADPH--hemoprotein reductase] androst-4-ene-3,17-dione + O2 + reduced [NADPH--hemoprotein reductase] = 19-hydroxyandrost-4-ene-3,17-dione + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] 19-hydroxyandrost-4-ene-3,17-dione + O2 + reduced [NADPH--hemoprotein reductase] = 19-oxo-androst-4-ene-3,17-dione + H(+) + 2 H2O + oxidized [NADPH--hemoprotein reductase] 19-oxo-androst-4-ene-3,17-dione + O2 + reduced [NADPH--hemoprotein reductase] = estrone + formate + 2 H(+) + H2O + oxidized [NADPH--hemoprotein reductase] estrone + O2 + reduced [NADPH--hemoprotein reductase] = 2-hydroxyestrone + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] 17beta-hydroxy-5alpha-androstan-3-one + O2 + reduced [NADPH--hemoprotein reductase] = 17beta,19-dihydroxy-3-oxo-5alpha-androstanone + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] 17beta,19-dihydroxy-3-oxo-5alpha-androstanone + O2 + reduced [NADPH--hemoprotein reductase] = 17beta-hydroxy-3,19-dioxo-5alpha-androstanone + H(+) + 2 H2O + oxidized [NADPH--hemoprotein reductase] 17beta-hydroxy-3,19-dioxo-5alpha-androstanone + O2 + reduced [NADPH--hemoprotein reductase] = 17beta-hydroxy-3-oxo-19-nor-5alpha-androst-1-ene + formate + 2 H(+) + H2O + oxidized [NADPH--hemoprotein reductase] kcat is 0.060 sec(-1) with androst-4-ene-3,17-dione as substrate (PubMed:20385561). kcat is 0.13 sec(-1) with 19-oxo-androst-4-ene-3,17-dione (PubMed:20385561). kcat is 0.42 sec(-1) with androst-4-ene-3,17-dione as substrate (PubMed:20385561). kcat is 0.046 min(-1) with estrone as substrate (PubMed:22773874). kcat is 0.27 min(-1) with 17beta-hydroxy-5alpha-androstan-3-one as substrate (PubMed:22773874). kcat is 0.32 min(-1) with 17beta,19-dihydroxy-3-oxo-5alpha-androstanone as substrate (PubMed:22773874). kcat is 0.77 min(-1) with 17beta-hydroxy-3,19-dioxo-5alpha-androstanone as substrate (PubMed:22773874). Steroid hormone biosynthesis. Widely expressed, including in adult and fetal brain, placenta, skin fibroblasts, adipose tissue and gonads. Phosphorylated in vitro by PKA and PKG/PRKG1. These phosphorylations inhibit the catalytic activity as measured by estrone synthesis from androstenedione (36% decrease for PKA and 30% for PKG/PRKG1). The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the cytochrome P450 family. Aromatase entry