Phenylalanine

Abbrev. F, Phe
Full Name Phenylalanine
Side chain type
hydrophobic
Mass
165.19
pl
5.49
pK1(α-COOH)
2.20
pK2(α-+NH3)
9.31

Side chain -CH2C6H5
Hydro- phobic
yes
Polar
no
Charged
no
Small
no
Tiny
no
Aromatic or Aliphatic
Aromatic
van der Waals volume
135
Codon
UUU, UUC
Occurrence in proteins (%)
3.9

Remarks: Essential for humans. Phenylalanine, tyrosine, and tryptophan contain large rigid aromatic group on the side chain. These are the biggest amino acids. Like isoleucine, leucine and valine, these are hydrophobic and tend to orient towards the interior of the folded protein molecule.

The alpha-amino acid Phenylalanine exists in two forms, the D- and L- forms, which are enantiomers (mirror-image molecules) of each other. It has a benzyl side chain. Its name comes from its chemical structure's 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.
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. Its enantiomer, D-phenylalanine (DPA), can be synthesized artificially.

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 can be converted only into phenylethylamine.

The genetic disorder phenylketonuria 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, and other food products, which are labeled: "Phenylketonurics: Contains phenylalanine." The reason is not that phenylalanine is in the food per se. Aspartame (NutraSweet) is an ester that is hydrolyzed in the body to form phenylalanine, aspartic acid and methanol (wood alcohol), and it is the phenylalanine portion of aspartame which then builds up in the person with PKU.


The synthesized mix DL-Phenylalanine (DLPA), which is a combination of the D- and L- forms (e.g. a racemate: a racemic compound or mixture), is used as a nutritional supplement. Research indicates that DLPA can be an effective part of an overall program to fight chronic pain and depression in some cases, including the mood swings of premenstrual syndrome (PMS). Some sources contend that DLPA can increase energy and mental alertness, as well as heighten the ability to focus in individuals with attention deficit hyperactivity disorder (ADHD).

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.

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