oxidoreductase activity, acting on CH or CH2 groups heme A synthase activity https://github.com/geneontology/go-ontology/issues/29711 Catalysis of the reaction: Fe(II)-heme o + 2 acceptor + H2O = Fe(II)-heme a + 2 acceptor-H2. The conversion of heme o to heme a occcurs by two successive hydroxylations of the methyl group at C8 using water as the oxygen source. The first hydroxylation forms heme i, the second hydroxylation results in an unstable dihydroxymethyl group, which spontaneously dehydrates, resulting in the formyl group of heme A. 2025-02-13T12:39:18Z sjm RHEA:63388 EC:1.17.99.9 molecular_function GO:0120547 Reactome:R-HSA-2995334 MetaCyc:RXN-18399