oxidoreductase activity, acting on paired donors, with incorporation or reduction of molecular oxygen, another compound as one donor, and incorporation of one atom of oxygen sphingolipid C4-monooxygenase activity https://github.com/geneontology/go-ontology/issues/25981 https://github.com/geneontology/go-ontology/issues/30193 RHEA:55476 GO:0102772 RHEA:55808 MetaCyc:RXN-14250 RHEA:33599 Catalysis of the reaction: a dihydroceramide + 2 Fe(II)-[cytochrome b5] + 2 H+ + O2 = a phytoceramide + 2 Fe(III)-[cytochrome b5] + H2O. sphingolipid long-chain base 4-hydroxylase activity RHEA:46364 EC:1.14.18.5 RHEA:33679 RHEA:43116 Reactome:R-HSA-428260 molecular_function RHEA:81475