Homogentisate 1,2-dioxygenase

Homogentisate dioxygenase (HGD ) is the name for the enzyme that cleaves the homogentisate to 4 - maleylacetoacetate. This reaction step is essential for the breakdown of the amino acid tyrosine in the metabolism of all living beings. A deficiency of homogentisate dioxygenase leading to alkaptonuria, a metabolic disease, and the cause is always a mutation of the gene that contains the genetic code for the HGD enzyme.


The largest amounts of homogentisate dioxygenase are formed in the tissues of the prostate, the small and large intestine and the kidneys and the liver. The gene encoding the enzyme is located in humans on chromosome 3, locus q21 - q23 and comprises 54,100 base pairs with 14 exons. After transcription, produces a 1,713 -base-long mRNA and the final protein counts after translation 445 amino acids.

Catalyzed reaction

Structural formula of 4- Maleylacetoessigsäure

When enabled by HGD reaction is the iron (II )-dependent ring-opening of homogentisate molecule with simultaneous transmission of two oxygen atoms. Thus, the enzyme acts as a dioxygenase. There are no similarities to other enzymes with iron as a cofactor.