Only enzyme known to utilize 5-formyltetrahydrofolate (folinic acid) as substrate. Contributes to tetrahydrofolate metabolism in an alternative way of folate biosynthesis. May regulate carbon flow through the folate-dependent one-carbon metabolic network that supplies carbon for the biosynthesis of purines, thymidine and amino acids. (6S)-5-formyl-5,6,7,8-tetrahydrofolate + ATP = 5,10-methenyltetrahydrofolate + ADP + phosphate N-glycosylated. Abolishes methenyltetrahydrofolate synthase activity and leads to accumulation of folinic acid. Leads to a striking methionine deficiency when combined with ADE16 and ADE17, 2 isoenzymes involved in the purine synthesis. Present with 468 molecules/cell in log phase SD medium. Belongs to the 5-formyltetrahydrofolate cyclo-ligase family.