Category: Natural chemicals
Introduction and description
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.
In normal subjects, ingestion of tyrosine or phenylalanine stimulates prolactin (PRL) secretion. In patients with phenylketonuria (PKU), we found normal PRL responses to phenylalanine, demonstrating that conversion of phenylalanine to tyrosine is not necessary for PRL stimulation. PKU patients also showed greater PRL responses to tyrosine during dietary phenylalanine restriction than when consuming an unrestricted diet PMID: 1588831
Phenylalanine in humans may ultimately be metabolized into a range of different substances. The long long function dependency chains have not yet been explored.
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.
Marine organisms have been increasingly regarded as good sources of nutrients for the human diet. The amino acids, fatty acids and sterols profiles of the widely consumed echinoderms Paracentrotus lividus Lamarck (sea urchin), Holothuria forskali Chiaje (sea cucumber), the gastropod molluscs Aplysia fasciata Poiret and Aplysia punctata Cuvier (sea hares), from Portuguese waters, were established by GC-MS analysis.
Overall, 10 amino acids, 14 fatty acids and 4 sterols were determined.
In general, all species presented the 10 amino acids identified, with the exceptions of
- H. forskali, [sea cucumber] in which no glycine, proline, trans-4-hydroxy-proline or phenylalanine were found, and
- fasciata [sea hare] which did not contain proline.
Unsaturated fatty acids were predominant compounds, with those from the ω-6 series, being in higher amounts than their ω-3 homologues, and cholesterol being the main sterol. The amino acids, fatty acids and sterols qualitative and quantitative composition of A. fasciata, A. punctata and H. forskali is reported here for the first time. PMID: 23870975
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.
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!
References and further reading
- Mortell KH, Anderson DJ, Lynch JJ, et al. (March 2006). "Structure-activity relationships of alpha-amino acid ligands for the alpha2delta subunit of voltage-gated calcium channels". Bioorganic & Medicinal Chemistry Letters 16 (5): 1138–41. doi:10.1016/j.bmcl.2005.11.108. PMID 16380257.
- Glushakov, AV; Dennis, DM; Morey, TE; Sumners, C; Cucchiara, RF; Seubert, CN; Martynyuk, AE (2002). "Specific inhibition of N-methyl-D-aspartate receptor function in rat hippocampal neurons by L-phenylalanine at concentrations observed during phenylketonuria." Molecular psychiatry 7 (4): 359–67. doi:10.1038/sj.mp.4000976. PMID 11986979.
- Dr Duke's list of chemicals and activity for the Shallot 017969
- Dr Duke's list of Plants containing PHENYLALANINE 017936
- Dr Duke’s list of Chemicals and their Biological Activities in: Cucurbita pepo L. (Cucurbitaceae) -- Zucchini 027494
- Growth conditions, elemental accumulation and induced physiological changes in Chinese cabbage 017790