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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 is an enzyme that usually bonds to form tetramers in bacteria and dimers in eukaryotes and has a subunit mass of 40-50 kDa. [7] [8] [9] Dividing the enzyme into the N-terminus and C-terminus one will notice that the N-terminus varies in composition while the C-terminus remains relatively constant [10] (the C-terminus in plants does differ slightly from the C-terminus in other beings).
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 ...
Specific targets include 4-hydroxyphenylpyruvic acid dioxygenase (hppD) and indolepyruvate ferredoxin oxidoreductase (ior). These enzymes are involved in phenylalanine and tyrosine catabolism. Other possible targets include glycerol kinase and substrate binding proteins in ATP-binding cassette transporters (ABC transporters). [ 5 ]
Federal stats presented at a June forum showed that out of 625,000 eligible physicians nationwide, only 25,000 are certified to prescribe buprenorphine. A mere 2.5 percent of all primary care doctors have gone through the certification process. “I cannot say it enough,” said then-Sen. Carl Levin (D-Mich.) at the meeting.
Phenylpyruvate tautomerase has also been found to exhibit the same keto-enol tautomerism for 4-Hydroxyphenylpyruvic acid, which is structurally similar to phenylpyruvate but contains an additional hydroxyl moiety in the para position of the aromatic ring.