PAH

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For other uses, see PAH (disambiguation).

PAH (phenylalanine hydroxylase) is a human gene that provides instructions for making an enzyme called phenylalanine hydroxylase. Phenylalanine hydroxylase is responsible for the first step in processing the amino acid phenylalanine, which is a building block of proteins. Phenylalanine is obtained through the diet, including some artificial sweeteners. Phenylalanine hydroxylase is responsible for the conversion of phenylalanine to another amino acid, tyrosine. Tyrosine is necessary for the production of certain hormones, chemicals that transmit signals in the brain (neurotransmitters), and a pigment (melanin) that gives hair and skin their color. Phenylalanine hydroxylase must work together with a substance called tetrahydrobiopterin (BH4), to function properly.

The PAH gene is located on the long (q) arm of chromosome 12 between positions 22 and 24.2, from base pair 101,734,570 to base pair 101,813,847.

1 Related conditions
2 See also
3 References
4 External links

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Related conditions

Phenylketonuria (PKU) is caused by mutations in the PAH gene. More than 450 mutations in the PAH gene have been identified in people with phenylketonuria. Although no single mutation accounts for all cases of PKU, some mutations are more common than others. Most of the known mutations cause a switch in a single amino acid in the phenylalanine hydroxylase enzyme. The most common mutation is a substitution of the amino acid arginine with the amino acid tryptophan at position 408 in the enzyme (written as Arg408Trp or R408W).

PAH mutations reduce the activity of phenylalanine hydroxylase, which allows phenylalanine to build up to toxic levels in the bloodstream and other tissues. Classic PKU, the most severe form of the disorder, occurs when phenylalanine hydroxylase activity is severely reduced or absent. As a result, people with untreated classic PKU have very high levels of phenylalanine that cause brain damage. Mutations in the PAH gene that allow some enzyme activity cause mild or moderate forms of PKU.

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