A cytochrome P450 monooxygenase involved in retinoid metabolism. Hydroxylates all trans-retinoic acid (atRA) to 4-hydroxyretinoate and may modulate atRA signaling and clearance. 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). an organic molecule + O2 + reduced [NADPH--hemoprotein reductase] = an alcohol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] all-trans-retinoate + O2 + reduced [NADPH--hemoprotein reductase] = all-trans-4-hydroxyretinoate + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Cofactor metabolism; retinol metabolism. Belongs to the cytochrome P450 family.