Formimidoyltetrahydrofolate cyclodeaminase

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

5-formimidoyltetrahydrofolate ${\displaystyle \rightleftharpoons }$ 5,10-methenyltetrahydrofolate + NH₃

formimidoyltetrahydrofolate cyclodeaminase
Identifiers
EC no.	4.3.1.4
CAS no.	9032-05-7
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Gene Ontology	AmiGO / QuickGO
Search PMC articles PubMed articles NCBI proteins

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]

Structural studies

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