phenylalanine n : an essential amino acid found in proteins and needed for growth of children and for protein metabolism in children and adults; abundant in milk and eggs; it is normally converted to tyrosine in the human body

English

Noun

1. An essential amino acid C9H11NO2 found in most animal proteins; it is essential for growth; the inability to metabolize it leads to phenylketonuria; it is a constituent of aspartame.

Translations

External links

Phe redirects here. For the BitTorrent feature, see PHE. For the constellation, see Phoenix (constellation).

Phenylalanine (abbreviated as Phe or F) is an α-amino acid with the formula HO2CCH(NH2)CH2C6H5. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. The codons for L-phenylalanine are UUU and UUC. It is a white, powdery solid. L-Phenylalanine (LPA) is an electrically-neutral amino acid, one of the twenty common amino acids used to biochemically form proteins, coded for by DNA.

Biosynthesis

Breast milk from mammals is rich in phenylalanine. It is also produced by plants and most microorganisms from prephenate, an intermediate on the shikimate pathway.

Prephenate is decarboxylated with loss of the hydroxyl group to give phenylpyruvate. This species is transaminated using glutamate as the nitrogen source to give phenylalanine and α-ketoglutarate.

Other biological roles

L-phenylalanine can also be converted into L-tyrosine, another one of the DNA-encoded amino acids. L-tyrosine in turn is converted into L-DOPA, which is further converted into dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline) (the latter three are known as the catecholamines).

Phenylalanine uses the same active transport channel as tryptophan to cross the blood-brain barrier, and, in large quantities, interferes with the production of serotonin.

Lignin is derived from phenylalanine and from tyrosine. Phenylalanine is converted to cinnamic acid by the enzyme phenylalanine ammonia lyase. and they must be labeled with a warning "Contains a source of phenylalanine". These warnings are specifically placed to aid individuals who suffer from PKU so that they can avoid such foods.

Geneticists have recently sequenced the genome of macaques. Their investigations have found "some instances where the normal form of the macaque protein looks like the diseased human protein" including markers for PKU.

D- and DL-phenylalanine

The unnatural stereoisomer D-phenylalanine (DPA) is available through conventional organic synthesis either as a single enantiomer or as a component of the racemic mixture. It does not participate in protein biosynthesis although it is found in proteins, in small amounts, particularly aged proteins and food proteins that have been processed. The biological functions of D-amino acids remain unclear. Some D-amino acids, such as D-phenylalanine, may have pharmacological activity.

DL-Phenylalanine is marketed as a nutritional supplement for its putative analgesic and antidepressant activities. The putative analgesic activity of DL-phenylalanine may be explained by the possible blockage by D-phenylalanine of enkephalin degradation by the enzyme carboxypeptidase A. The mechanism of DL-phenylalanine's putative antidepressant activity may be accounted for by the precursor role of L-phenylalanine in the synthesis of the neurotransmitters norepinephrine and dopamine. Elevated brain norepinephrine and dopamine levels are thought to be associated with antidepressant effects. D-Phenylalanine is absorbed from the small intestine, following ingestion, and transported to the liver via the portal circulation. A fraction of D-phenylalanine appears to be converted to L-phenylalanine. D-Phenylalanine is distributed to the various tissues of the body via the systemic circulation. D-Phenylalanine appears to cross the blood-brain barrier with less efficiency than L-phenylalanine. A fraction of an ingested dose of D-phenylalanine is excreted in the urine.

History

The genetic codon for phenylalanine was first discovered by Marshall W. Nirenberg in 1959. He showed that by using m-RNA to insert multiple uracil repeats into the bacterium E. coli, the bacterium produced a new protein consisting solely of repeated phenylalanine amino acids. This discovery lead to the determination of the relationship between RNA and amino acids, which was foundational to the understanding of the Genetic Code.

References

External links

• Phenylalanine and tyrosine biosynthesis
• Computational Chemistry Wiki
• Nitrogen Order's Molecule of the Week
• DL-phenylalanine versus imipramine in depression