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. 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. 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. Also displays 2-hydroxylase activity toward estrone. 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). 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] Steroid hormone biosynthesis. Belongs to the cytochrome P450 family.