Formimidoyltetrahydrofolate cyclodeaminase

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

:5-formimidoyltetrahydrofolate $ightleftharpoons$ 5,10-methenyltetrahydrofolate + NH₃

Hence, this enzyme has one substrate, 5-formimidoyltetrahydrofolate, and two products, 5,10-methenyltetrahydrofolate and NH₃. [cite journal | author = Rabinowitz JC and Pricer WE | date = 1956 | title = Formiminotetrahydrofolic acid and methenyltetrahydrofolic acid as intermediates in the formation of N10-formyltetrahydrofolic acid | journal = J. Am. Chem. Soc. | volume = 78 | pages = 5702–5704 | doi = 10.1021/ja01602a073 ]

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. [cite journal |author=MacKenzie RE, Aldridge M, Paquin J |title=The bifunctional enzyme formiminotransferase-cyclodeaminase is a tetramer of dimers |journal=J. Biol. Chem. |volume=255 |issue=19 |pages=9474–8 |year=1980 |pmid=7410436 |url=http://www.jbc.org/cgi/reprint/255/19/9474] 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. [cite journal |author=Kohls D, Sulea T, Purisima EO, MacKenzie RE, Vrielink A |title=The crystal structure of the formiminotransferase domain of formiminotransferase-cyclodeaminase: implications for substrate channeling in a bifunctional enzyme |journal=Structure |volume=8 |issue=1 |pages=35–46 |year=2000 |pmid=10673422 |doi=10.1016/S0969-2126(00)00078-2]

tructural studies

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

References

External links

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

Gene Ontology (GO) codes