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Tyrosinemia type III is a rare disorder caused by a deficiency of the enzyme 4-hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27), encoded by the gene HPD. [2] This enzyme is abundant in the liver, and smaller amounts are found in the kidneys. It is one of a series of enzymes needed to break down tyrosine.
The gene affected is the HPD gene encoding 4-hydroxyphenylpyruvic acid dioxygenase, on chromosome 12q24. [4] It is unusual in that most other inborn errors of metabolism are caused by loss-of-function mutations, and hence have recessive inheritance (condition occurs only if both copies are mutated).
HPPD also catalyzes the conversion of phenylpyruvate to 2-hydroxyphenylacetate and the conversion of α-ketoisocaproate to β-hydroxy β-methylbutyrate. [2] [3] HPPD is an enzyme that is found in nearly all aerobic forms of life. [4] This reaction shows the conversion of 4-hydroxyphenylpyruvate into homogentisate by HPPD.
4-Hydroxyphenylpyruvic acid (4-HPPA) is an intermediate in the metabolism of the amino acid phenylalanine. The aromatic side chain of phenylalanine is hydroxylated by the enzyme phenylalanine hydroxylase to form tyrosine. The conversion from tyrosine to 4-HPPA is in turn catalyzed by tyrosine aminotransferase. [2]
4-Hydroxyphenylpyruvate dioxygenase (HPPD) is an enzyme found in both plants and animals, which catalyzes the catabolism of the amino acid tyrosine. [4] Preventing the breakdown of tyrosine has three negative consequences: the excess of tyrosine stunts growth; the plant suffers oxidative damage due to lack of tocopherols (vitamin E); and ...
Patients typically have normal levels of 5-hydroxyindolacetic acid (5HIAA), low levels of homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylethylene glycol (MHPG), and a low HVA:5-HIAA ratio. [1] Upon finding a pattern of CSF abrormalities suggestive of the disease, the diagnosis may be confirmed by analysing the TH gene encoding the enzyme. [1]
In enzymology, a 3,4-dihydroxyphenylacetate 2,3-dioxygenase (EC 1.13.11.15) is an enzyme that catalyzes the chemical reaction 3,4-dihydroxyphenylacetate + O 2 ⇌ {\displaystyle \rightleftharpoons } 2-hydroxy-5-carboxymethylmuconate semialdehyde
In enzymology, a 4-hydroxyphenylpyruvate oxidase (EC 1.2.3.13) is an enzyme that catalyzes the chemical reaction. 4-hydroxyphenylpyruvate + 1/2 O 2 4-hydroxyphenylacetate + CO 2. Thus, the two substrates of this enzyme are 4-hydroxyphenylpyruvate and O 2, whereas its two products are 4-hydroxyphenylacetate and CO 2.