This results in a build-up of homogentisic acid, an intermediary product in the metabolism of phenylalanine and tyrosine. The excess homogentisic acid is oxidized and polymerized and forms a blackish pigment, alkapton, which is deposited in cartilage and can be easily seen in the cartilage of the ears.

What is homogentisic acid in the body?

Homogentisic acid is a dihydroxyphenylacetic acid having the two hydroxy substituents at the 2- and 5-positions. It has a role as a human metabolite and a plant metabolite.

What is the Alkaptonuria?

Alkaptonuria, or “black urine disease”, is a very rare inherited disorder that prevents the body fully breaking down two protein building blocks (amino acids) called tyrosine and phenylalanine. It results in a build-up of a chemical called homogentisic acid in the body.

What is the origin of a homogentisic acid?

Homogentisic acid (2,5-dihydroxyphenylacetic acid) is a phenolic acid usually found in Arbutus unedo (strawberry-tree) honey. It is also present in the bacterial plant pathogen Xanthomonas campestris pv. phaseoli as well as in the yeast Yarrowia lipolytica where it is associated with the production of brown pigments.

What causes high homogentisic acid?

Alkaptonuria is a rare inherited disorder. It occurs when your body can’t produce enough of an enzyme called homogentisic dioxygenase (HGD). This enzyme is used to break down a toxic substance called homogentisic acid. When you don’t produce enough HGD, homogentisic acid builds up in your body.

Is homogentisic acid an amino acid?

These two amino acids also play a role in making certain hormones, pigments, and brain chemicals called neurotransmitters. Homogentisate oxidase is responsible for a specific step in the breakdown of phenylalanine and tyrosine. Previous steps convert the two amino acids into a molecule called homogentisic acid.

Is homogentisic acid present in the urine of healthy people?

Excess homogentisic acid and related compounds are deposited in connective tissues , which causes cartilage and skin to darken. Over time, a buildup of this substance in the joints leads to arthritis. Homogentisic acid is also excreted in urine, making the urine turn dark when exposed to air.

What causes alkaptonuria?

A defect in the HGD gene causes alkaptonuria. The gene defect makes the body unable to properly break down certain amino acids (tyrosine and phenylalanine). As a result, a substance called homogentisic acid builds up in the skin and other body tissues. The acid leaves the body through the urine.

What is phenylketonuria and alkaptonuria?

Alkaptonuria is a recessive genetic deficiency resulting in the incomplete oxidation of tyrosine and phenylalanine, causing increased levels of homogentisic (or melanic) acid. It is also known as phenylketonuria and ochronosis.

What is homogentisic acid in urine?

Homogentisic acid (HGA) is a diagnostic metabolite that accumulates in the urine and tissues of patients with alkaptonuria which is a rare autosomal recessive disease. HGA is a specific metabolite in urine and serum, which is used for diagnosis of alkaptonuria.

How can homogentisic acid be reduced?

Treatment with ascorbic acid twice daily may reduce the connective tissue damage, and affected children have also been placed on a low protein diet. Nitisinone therapy may decrease homogentisic acid production.

Is homogentisic acid an enzyme?

Homogentisate 1,2-dioxygenase (homogentisic acid oxidase, homogentisate oxidase, homogentisicase) is an enzyme which catalyzes the conversion of homogentisate to 4-maleylacetoacetate.

What is homogentisic acid found in?

Homogentisic acid. Homogentisic acid (2,5-dihydroxyphenylacetic acid) is a phenolic acid usually found in Arbutus unedo (strawberry-tree) honey. It is also present in the bacterial plant pathogen Xanthomonas campestris pv. phaseoli as well as in the yeast Yarrowia lipolytica where it is associated with the production of brown pigments.

What is the reaction between homogentisate and HGD?

HGD appears in the metabolic pathway of tyrosine and phenylalanine degradation once the molecule homogentisate is produced. Homogentisate reacts with HGD to produce maleylacetoacetate, which then is further used in the metabolic pathway. HGD requires the use of Fe 2+ and O 2 in order to cleave the aromatic ring of homogentisate.

What is the pathophysiology of homogentisate deficiency?

The deficiency of homogentisate 1,2 dioxygenate (HGD) leads to an accumulation of homogentisic acid (HGA) in plasma and urine which auto-oxidizes in tissues into benzoquinone acetic acid and polymerizes to an ochronotic pigment.

What is homhomogentisic acid?

homogentisic acid. a compound that is an intermediate product of the metabolism of tyrosine. It forms a melanin-like staining substance in the urine of people who have alkaptonuria.