Plays a key role in retinoic acid metabolism. Appears to be involved in the inactivation of all-trans-retinoic acid (RA). all-trans-retinoate + O2 + reduced [NADPH--hemoprotein reductase] = all-trans-4-hydroxyretinoate + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Belongs to the cytochrome P450 family.