Formimidoyltetrahydrofolate cyclodeaminase

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In enzymology, a formimidoyltetrahydrofolate cyclodeaminase (EC 4.3.1.4) is an enzyme that catalyzes the chemical reaction

5-formimidoyltetrahydrofolate $\rightleftharpoons$ 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 2.1.2.5), 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]

1 Structural studies
2 References
3 External links
- 3.1 Gene Ontology (GO) codes

[edit] Structural studies

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

[edit] References

^ 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: 5702–5704. doi:10.1021/ja01602a073.
^ 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.
^ 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. doi:10.1016/S0969-2126(00)00078-2. PMID 10673422.