Phenylalanine

Ah yes. *That* old thing. Well, here goes:

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 the fact that its chemical structure consists 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.

* Structural chemical formula: NH2CH(CH2C6H5)COOH
* pK1 (α-COOH): 2.20
* pK2 (α-NH3+): 9.31
* Protein Occurrence: 3.9%

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, norepinephrine, and epinephrine. D-phenylalanine can only be converted into phenylethylamine.

The genetic disorder phenylketonuria is an inability to metabolize phenylalanine.

The synthesized mix DL-Phenylalanine (DLPA), which is a combination of the D- and L- forms, is used as a nutritional supplement.

Phenylalanine is part of the composition of aspartame, a common sweetener found in prepared foods (particularly soft drinks, and gum). Due to phenylketonuria, products containing aspartame usually have a warning label that they contain phenylalanine, in compliance with U.S. FDA guidelines.

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 a hidden danger to anyone consuming aspartame. Most consumers don't know that too much Phenylalanine is a neurotoxin and excites the neurons in the brain to the point of cellular death.

ADD/ADHD, emotional and behavioral disorders can all be triggered by too much Phenylalanine in the daily diet. If you are one in ten thousand people who are PKU or carry the PKU gene, Phenylalanine can cause irreversible brain damage and death, especially when used in high quantities or during pregnancy. Phenylalanine is 50% of aspartame, and to the degree humans consume diet products, Phenylalanine levels are reaching a dangerous peak.

The 1976 Groliers encyclopedia states cancer cannot live without phenylalanine. Phenylalanine makes up 50% of aspartame.

Phenylalanine is one of the essential amino acids found in proteins.

Phenylalanine is found naturally in foods such as eggs, milk, bananas, and meat. If you are PKU (Phenylketonuric) or sensitive to phenylalanine, you will react to the phenylalanine in aspartame. You may want to get a blood test to check for this condition. Over the past 20 years, humans have become more aware of PKU reactions because human beings began using isolated phenylalanine to the degree it is harmful to some individuals, many as aspartame side effects.


Hope that helps.