methylenetetrahydrofolate UK /ˌmɛ.θɪ.liːnˌtɛ.tɹəˌhʌɪ.dɹə(ʊ)ˈfəʊ.leɪt/US /ˌmɛ.θə.liːnˌtɛ.tɹəˌhaɪ.dɹəˈfoʊ.leɪt/ noun1 •The substrate used by the enzyme methylenetetrahydrofolate reductase to generate 5-methyltetrahydrofolate (levomefolic acid). formsmethylenetetrahydrofolates