A cytochrome P450 monooxygenase involved in the metabolism of all-trans retinoic acid (atRA), a signaling molecule that binds to retinoic acid receptors and regulates gene transcription. May regulate at-RA signaling during hindbrain development (PubMed:9857192). 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). Catalyzes the hydroxylation of carbon hydrogen bonds of atRA primarily at C-4. Has no activity toward 9-cis and 13-cis retinoic acid stereoisomers. May play a role in the oxidative metabolism of xenobiotics such as tazarotenic acid (By similarity). all-trans-retinoate + O2 + reduced [NADPH--hemoprotein reductase] = all-trans-(4S)-hydroxyretinoate + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Expressed primarily in ovary, brain and eyes. At the onset of gastrulation, expressed within the marginal zone and in the dorsal animal hemisphere. In advanced gastrulae (stage 13), detected in the prospective neuroectoderm and the underlying involuted mesoderm, in an area that corresponds to the prechordal plate. At stage 14, expressed in the cement gland anlage, the mid-/hindbrain boundary and the auditory placodes. At tadpole stages of development, most prominent in the first, second and third branchial arch, in the lens epithelium and in the posterior dorsal fin, as well as in the posterior wall of the tail tip. By retinoic acid. Belongs to the cytochrome P450 family.