Formimidoyltetrahydrofolate cyclodeaminase

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In enzymology, a formimidoyltetrahydrofolate cyclodeaminase (EC is an enzyme that catalyzes the chemical reaction

5-formimidoyltetrahydrofolate 5,10-methenyltetrahydrofolate + NH3

Hence, this enzyme has one substrate, 5-formimidoyltetrahydrofolate, and two products, 5,10-methenyltetrahydrofolate and NH3.[1]

This enzyme belongs to the family of lyases, specifically ammonia lyases, which cleave carbon-nitrogen bonds. The systematic name of this enzyme class is 5-formimidoyltetrahydrofolate ammonia-lyase (cyclizing 5,10-methenyltetrahydrofolate-forming). Other names in common use include formiminotetrahydrofolate cyclodeaminase, and 5-formimidoyltetrahydrofolate ammonia-lyase (cyclizing). This enzyme participates in folate metabolism by catabolising histidine and adding to the C1-tetrahydrofolate pool.

In mammals, this enzyme can be found as part of a bifunctional enzyme in a single polypeptide with glutamate formimidoyltransferase (EC, the enzyme activity that catalyses the previous step in the histidine catabolic pathway.[2] This arrangement allows the 5-formimidoyltetrahydrofolate intermediate to move directly from one active site to another without being released into solution, in a process called substrate channeling.[3]

Structural studies

As of late 2007, 3 structures have been solved for this class of enzymes, with PDB accession codes 1O5H, 1TT9, and 2PFD.


  1. Rabinowitz JC and Pricer WE (1956). "Formiminotetrahydrofolic acid and methenyltetrahydrofolic acid as intermediates in the formation of N10-formyltetrahydrofolic acid". J. Am. Chem. Soc. 78: 5702&ndash, 5704.
  2. MacKenzie RE, Aldridge M, Paquin J (1980). "The bifunctional enzyme formiminotransferase-cyclodeaminase is a tetramer of dimers". J. Biol. Chem. 255 (19): 9474–8. PMID 7410436.
  3. Kohls D, Sulea T, Purisima EO, MacKenzie RE, Vrielink A (2000). "The crystal structure of the formiminotransferase domain of formiminotransferase-cyclodeaminase: implications for substrate channeling in a bifunctional enzyme". Structure. 8 (1): 35–46. PMID 10673422.

External links

The CAS registry number for this enzyme class is 9032-05-7.

Gene Ontology (GO) codes