Phenylalanine  is an essential amino acid.  It is a precursor for tyrosine, the monoamine signaling molecules dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), and the skin pigment melanin.  It also appears to be an essential precursor to prolactin – a very key hormone during pregnancy.

Phenylalanine in humans may ultimately be metabolized into a range of different substances.  The long long function dependency chains have not yet been explored.

Sources

 

Phenylalanine is found naturally in the breast milk of mammals, but it is found in a considerable number of plants.  We have included an observation derived from Dr Duke’s phytochemical database to show all the plants in which it can be found.

In addition to plants, it can be found in oily fish, all meat – beef, pork, lamb, chicken, turkey, veal, game meats and so on.  It is present in high quantities in many hard cheeses or rich creamy cheeses such as Brie, Camembert or Stilton.  And of course milk and milk products such as buttermilk or yoghurt.

It is known to be present in lobster and crab, but as more research is undertaken some interesting new sources in sea based animals is coming to light.

There are other fascinating sources for phenylalanine which have yet to be explored.

J. Heinrich Matthaei and Marshall W. Nirenberg,  in 1961, for example, showed that by using m-RNA to insert multiple uracil repeats into the genome of the bacterium E. coli, they could cause the bacterium to produce a polypeptide consisting solely of repeated phenylalanine amino acids. The information was used in genome research, but given the findings on intestinal bacteria, we may find this research opens other fascinating avenues of discovery on how the intestine works and its flora.  An ecosystem yet to be explored!

Imbalance - overdose

 

The use of supplements risks overdose and some very very nasty side effects.  Phenylalanine uses the same active transport channel as tryptophan to cross the blood–brain barrier. In excessive quantities, supplementation can interfere with the production of serotonin and other aromatic amino acids as well as nitric oxide due to the overuse (eventually, limited availability) of the associated cofactors, iron or tetrahydrobiopterin.

So to put this in simple terms it results in serotonin imbalance, as well as iron imbalance, and since nitric oxide plays a part in blood circulation, possible blood circulatory disease.

A non-food source of phenylalanine is the artificial sweetener aspartame. This compound, sold under the trade names Equal and NutraSweet, is metabolized by the body into several chemical by-products including phenylalanine.  If many foods containing this sweetener are ingested, it would amount to an overdose.

Imbalance - deficiency

The genetic disorder phenylketonuria (PKU) is the inability to metabolize phenylalanine. Individuals with this disorder are known as "phenylketonurics" and must regulate their intake of phenylalanine.

The breakdown problems phenylketonurics have with protein and the attendant buildup of phenylalanine in the body also occurs with the ingestion of aspartame.  Accordingly, all products in Australia, the U.S. and Canada that contain aspartame must be labeled: "Phenylketonurics: Contains phenylalanine." In the UK, foods containing aspartame must carry ingredient panels that refer to the presence of "aspartame or E951" and they must be labeled with a warning "Contains a source of phenylalanine." In Brazil, the label "Contém Fenilalanina" (Portuguese for "Contains Phenylalanine") is also mandatory in products which contain it.

These warnings are placed to aid individuals who have been diagnosed with PKU so that they can avoid such foods, but it also a helpful guide to those without the disease to ensure they do not overdose.

False marketing and supplements

 

The stereoisomer D-phenylalanine (DPA) is found in proteins in small amounts - particularly old stale proteins and food proteins that have been processed. The biological functions of D-amino acids ‘remain unclear’.  There is some concern that DPA effectively antagonises the activities of niacin – an essential vitamin.

Despite this, DL-Phenylalanine (DLPA) is being marketed as a ‘nutritional supplement’ for its supposed ‘analgesic and antidepressant’ activities. DL-Phenylalanine is a mixture of D-phenylalanine and L-phenylalanine. L-Phenylalanine is an antagonist at α2δ Ca2+ calcium channels, as such it is a sort of calcium channel blocker, hardly nutritional – in fact extremely pharmaceutical!