An iron-sulfur flavoprotein that also contains zinc. The enzyme from Clostridium formicoaceticum catalyses the reduction of methylene blue, menadione, benzyl viologen, rubredoxin or FAD with 5-methyltetrahydrofolate and the oxidation of reduced ferredoxin or FADH2 with 5,10-methylenetetrahydrofolate. However, unlike EC 1.5.1.20, methylenetetrahydrofolate reductase [NAD(P)H], there is no activity with NAD(P)H.