oxidoreductase activity, acting on paired donors, with incorporation or reduction of molecular oxygen, reduced pteridine as one donor, and incorporation of one atom of oxygen mandelate 4-monooxygenase activity https://github.com/geneontology/go-ontology/issues/30193 mandelic acid 4-hydroxylase activity RHEA:21716 Catalysis of the reaction: (S)-mandelate + 5,6,7,8-tetrahydrobiopterin + O2 = (S)-4-hydroxymandelate + 7,8-dihydrobiopterin + H2O. (S)-2-hydroxy-2-phenylacetate is also known as S-mandelate. L-mandelate 4-hydroxylase activity (S)-2-hydroxy-2-phenylacetate,tetrahydrobiopterin:oxygen oxidoreductase (4-hydroxylating) GO:0050481 molecular_function MetaCyc:MANDELATE-4-MONOOXYGENASE-RXN KEGG_REACTION:R03794 EC:1.14.16.6