PhyH

phytanoyl-CoA dioxygenase
The structure of human PAHX (PDB: 2A1X​). The Fe(II) cofactor is shown as an orange sphere, coordinated by two histidine and one aspartate residue (shown in green) and by the 2-oxoglutarate cosubstrate (shown in yellow).
Identifiers
EC number	1.14.11.18
CAS number	185402-46-4
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 / EGO
Search PMC articles PubMed articles NCBI proteins

In enzymology, a phytanoyl-CoA dioxygenase (EC 1.14.11.18) is an enzyme that catalyzes the chemical reaction

The three substrates of this enzyme are phytanoyl-CoA, 2-oxoglutarate (2OG), and O₂, whereas its three products are 2-hydroxyphytanoyl-CoA, succinate, and CO₂.

This enzyme belongs to the family of iron(II)-dependent oxygenases, which typically incorporate one atom of dioxygen into the substrate and one atom into the succinate carboxylate group. The mechanism is complex, but is believed to involve ordered binding of 2-oxoglutarate to the iron(II) containing enzyme followed by substrate. Binding of substrate causes displacement of a water molecule from the iron(II) cofactor, leaving a vacant coordination position to which dioxygen binds. A rearrangement occurs to form a high energy iron-oxygen species (which is generally thought to be an iron(IV)=O species) that performs the actual oxidation reaction.

The systematic name of this enzyme class is phytanoyl-CoA, 2-oxoglutarate:oxygen oxidoreductase (2-hydroxylating). This enzyme is also called phytanoyl-CoA hydroxylase.

In humans, phytanoyl-CoA hydroxylase is encoded by the PHYH (aka PAHX) gene and is required for the alpha-oxidation of branched chain fatty acids (e.g. phytanic acid) in peroxisomes. PHYH deficiency results in the accumulation of large tissue stores of phytanic acid and is the major cause of Refsum disease.