Phenylalanine

Also known as:
L-phenylalanine
beta-phenylalanine
alpha-aminohydrocinnamic acid
(S)-2-amino-3- phenylpropanoic acid
alpha-amino-beta-phenylpropionic acid
Abbreviated as Phe or F

Chemical formula:
C₉H₁₁NO₂

Structural formula:
     H        H                      
      \      /                       
       C == C      H    H      O     
      /      \     |    |     //     
H -- C        C -- C -- C -- C -- O  
      \\    //     |    |          \ 
       C -- C      H    N           H
      /      \         / \           
     H        H       H   H          
(Based on original ASCII art from Tyrosine by jafuser)

L-phenylalanine, or just phenylalanine, is one of the essential amino acids that the body cannot produce on its own, it needs to be ingested as food. Being an amino acid, phenylalanine is found in foods high in protein. It has however been artificially isolated and can be found as an ingredient in other products, such as dietary supplements and the artificial sweetener aspartame (phenylalanine makes up 50% of aspartame).

Phenylalanine is processed by an enzyme called phenylalanine hydroxylase into tyrosine, which is in turn used to make neurotransmitters such as dopamine and norepinephrine. There is a very rare genetic disorder called Phenylketonuria (PKU) which causes a lack of the phenylalanine hydroxylase enzyme. Phenylketonuric individuals must follow a special low protein diet to limit their phenylalanine intake because their bodies cannot process it, instead allowing it to build up in the blood stream as phenylpyruvic acid, which results in a number of mental and physical disorders. Aspartame sweeteners, sold under brand names such as Equal and NutriSweet, are very popular in diet products. Due to their high levels of phenylalanine, these products are required by the FDA to bear the warning Phenylketonurics: contains phenylalanine.

The stereoisomer (molecular three-dimensional mirror image) of L-phenylalanine (the version discussed above) is D-phenylalanine. D-phenylalanine is not naturally occurring but can be synthesized in a laboratory and is used as a nutritional supplement.

Sources:
http://www.ess.sunysb.edu/tracy/whatis.html
http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/lph_0201.shtml
http://www.lef.org/protocols/prtcl-089.shtml
http://en.wikipedia.org/wiki/Phenylalanine
http://www.sweetpoison.com/phenylalanine.html