Phenylalanine

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Phenylalanine
Systematic name	2-Amino-3-phenyl- propanoic acid
Abbreviations	Phe F
Chemical formula	C₉H₁₁NO₂
Molecular mass	165.19 g mol^-1
Melting point	283 °C
Density	1.29 g cm^-3
Isoelectric point	5.5
pK_a	2.20 9.09
CAS number	[673-06-3] (D) [63-91-2] (L) [150-30-1] (D/L or racemic)
SMILES	C1=CC=C(C=C1)CC(C(=O)O)N
Image:L-phenylalanine-skeletal.png Image:L-phenylalanine-3D-sticks.png
Disclaimer and references

Phe redirects here. For the BitTorrent feature, see PHE.

Phenylalanine is an essential alpha-amino acid. It exists in two forms, a D and an L form, which are enantiomers (mirror-image molecules) of each other. It has a benzyl side chain. Its name comes from its chemical structures consisting of a phenyl group substituted for one of the hydrogens in the side chain of alanine. Because of its phenyl group, phenylalanine is an aromatic compound. At room temperature, it is a white, powdery solid.

1 Forms
2 Biological aspects
3 References
4 External links

[edit] Forms

L-phenylalanine

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. L-phenylalanine is used in living organisms, including the human body, where it is an essential amino acid. L-phenylalanine can also be converted into L-tyrosine, another one of the twenty protein-forming amino acids. L-tyrosine is converted into L-DOPA, which is further converted into dopamine, norepinephrine, and epinephrine (latter three are known as the catecholamines).

D-phenylalanine

D-phenylalanine (DPA), can be synthesized artificially. D-phenylalanine can be converted only into phenylethylamine. D-phenylalanine is a non-protein amino acid, meaning that it does not participate in protein biosynthesis. D-phenylalanine and other D-amino acids are, however, 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 pharmacologic activity.

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.

DL-phenylalanine

DL-phenylalanine is a racemic mixture of phenylalanine - it contains 50 % each of D and L enantiomers. DL-Phenylalanine is marketed as a nutritional supplement for its putative analgesic and antidepressant activities.^{[citation needed]}

[edit] Biological aspects

The genetic codon for phenylalanine was the first to be discovered. Marshall W. Nirenberg discovered that, when he inserted m-RNA made up of multiple uracil repeats into E. coli, the bacterium produced a new protein, made up solely of repeated phenylalanine amino acids.

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.

Phenylalanine is contained in most protein rich foods, but especially good sources are dairy products (curd, milk, cottage cheese), avocados, pulses and legumes (particularly peanuts and lima beans), nuts (pistachios, almonds), seeds (piyal seeds), leafy vegetables, whole grains, poultry, fish and other seafoods.

Image:DLPA RXN.GIF

[edit] Absorption

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. There is much about the pharmacokinetics in humans that is unknown.

[edit] Phenylketonuria

The genetic disorder phenylketonuria (PKU) is an inability to metabolize phenylalanine. Individuals with this disorder are known as "phenylketonurics", and must abstain from consumption of phenylalanine. It is present in many sugarless gums, Monster Munch crisps, sugarless soft drinks (such as Diet Coke) and a number of other food products, all of which must be labeled: "Phenylketonurics: Contains phenylalanine." It's important to realize that phenylalanine itself is not present in the food. Rather, the artificial sweetener aspartame (e.g. Equal, NutraSweet) is present. Aspartame is an ester that is hydrolyzed in the body to form phenylalanine, aspartic acid and methanol (wood alcohol), and it is the phenylalanine product of aspartame which then builds up in the person with PKU. The amounts produced by aspartame are an incredibly low risk factor however, as far larger quantities of the amino acid would be obtained through simply consuming any protein at all with phenylalanine content, which would include all complete proteins, as phenylalanine is an essential amino acid.

[edit] Biosynthesis

Phenylalanine cannot be made by animals, which have to obtain it from their diet. It is produced by plants and most microorganisms from prephenate, an intermediate on the shikimate pathway.

Image:Phenylalanine biosynthesis.png

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

[edit] References

[edit] External links

The 20 Common Amino Acids
Alanine (dp) \| Arginine (dp) \| Asparagine (dp) \| Aspartic acid (dp) \| Cysteine (dp) \| Glutamic acid (dp) \| Glutamine (dp) \| Glycine (dp) \| Histidine (dp) \| Isoleucine (dp) \| Leucine (dp) \| Lysine (dp) \| Methionine (dp) \| Phenylalanine (dp) \| Proline (dp) \| Serine (dp) \| Threonine (dp) \| Tryptophan (dp) \| Tyrosine (dp) \| Valine (dp)
←Peptides	Major families of biochemicals	Nucleic acids→