:Phenylalanine:

Function: antidepressant and pain reliever (DLPA).

Phenylalanine is an essential amino acid and the precursor for the amino acid tyrosine. Like tyrosine, it is the precursor of catecholamines in the body (tyramine, dopamine, epinephrine and norepinephrine). The psychotropic drugs (mescaline, morphine, codeine, and papaverine) also have phenylalanine as a constituent.

Phenylalanine is a precursor of the neurotransmitters called catecholamines, which are adrenalin-like substances. Phenylalanine is highly concentrated in the human brain and plasma. Normal metabolism of phenylalanine requires biopterin, iron, niacin, vitamin B6, copper and vitamin C. An average adult ingests 5 g of phenylalanine per day and may optimally need up to 8 g daily.

Phenylalanine is highly concentrated in high protein foods, such as meat, cottage cheese and wheat germ. A new dietary source of phenylalanine is artificial sweeteners containing aspartame. Aspartame appears to be nutritious except in hot beverages; however, it should be avoided by phenylketonurics and pregnant women. Phenylketonunics, who have a genetic error of phenylalanine metabolism, have elevated serum plasma levels of phenylalanine up to 400 times normal. Mild phenylketonuria can be an unsuspected cause of hyperactivity, learning problems, and other developmental problems in children.

We have found that about 10 percent of depressed patients have low plasma phenylalanine, and phenylalanine is an effective treatment in these cases. Elevated phenylalanine levels occur during infection. Phenylalanine levels are lowered by caffeine ingestion.

Phenylalanine can be an effective pain reliever. Its use in premenstrual syndrome and Parkinson's may enhance the effects of acupuncture and electric transcutaneous nerve stimulation (TENS). Phenylalanine and tyrosine, like L-dopa, produce a catecholamine effect. Phenylalanine is better absorbed than tyrosine and may cause fewer headaches.

Low phenylalanine diets have been prescribed for certain cancers with mixed results. Some tumors use more phenylalanine (particularly melatonin-producing tumors called melanoma). One strategy is to exclude this amino acid from the diet, i.e., a PKU diet. The other strategy is just to increase phenylalanine's competing amino acids, i.e., tryptophan, valine, isoleucine and leucine, but not tyrosine.

Form and Absorption of Phenylalanine

Phenylalanine is available as D, L or DL form; this refers to right (D = dextro) or left (L = levo) forms of spatial orientation of the molecules. DL-phenylalanine is a 50/50 (equimolar) mixture of D-phenylalanine and L-phenylalanine. D forms of amino acids are not normally used in humans. D-phenylalanine and D-methionine are the only known D amino acids that can be converted to their natural L forms by the action of liver.