4420 L-Phenylalanine Phenylalanine is an essential amino acid and the precursor of the amino acid tyrosine. Like tyrosine, phenylalanine is also a precursor for catecholamines including tyramine, dopamine, epinephrine, and norepinephrine. Catecholamines are neurotransmitters that act as adrenalin-like substances. Interestingly, several psychotropic drugs (mescaline, morphine, codeine, and papaverine) also have phenylalanine as a constituent. 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 a number of high protein foods, such as meat, cottage cheese, and wheat germ. An additional dietary source of phenylalanine is artificial sweeteners containing aspartame. As a general rule, aspartame should be avoided by phenylketonurics and pregnant women. When present in sufficiently high levels, phenylalanine can act as a neurotoxin and a metabotoxin. A neurotoxin is a compound that disrupts or attacks neural cells and neural tissue. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of phenylalanine are associated with at least five inborn errors of metabolism, including Hartnup disorder, hyperphenylalaninemia due to guanosine triphosphate cyclohydrolase deficiency, phenylketonuria (PKU), tyrosinemia type 2 (or Richner-Hanhart syndrome), and tyrosinemia type III (TYRO3). Phenylketonurics have elevated serum plasma levels of phenylalanine up to 400 times normal. High plasma concentrations of phenylalanine influence the blood-brain barrier transport of large neutral amino acids. The high plasma phenylalanine concentrations increase phenylalanine entry into the brain and restrict the entry of other large neutral amino acids (PMID: 19191004). Phenylalanine has been found to interfere with different cerebral enzyme systems. Untreated phenylketonuria (PKU) can lead to intellectual disability, seizures, behavioural problems, and mental disorders. It may also result in a musty smell and lighter skin. Classic PKU dramatically affects myelination and white matter tracts in untreated infants; this may be one major cause of neurological disorders associated with phenylketonuria. Mild phenylketonuria can act as an unsuspected cause of hyperactivity, learning problems, and other developmental problems in children. It has been recently suggested that PKU may resemble amyloid diseases, such as Alzheimer's disease and Parkinson's disease, due to the formation of toxic amyloid-like assemblies of phenylalanine (PMID: 22706200). Phenylalanine also has some potential benefits. Phenylalanine can act as 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-like effect. Phenylalanine is better absorbed than tyrosine and may cause fewer headaches. Low phenylalanine diets have been prescribed for certain cancers with mixed results. For instance, some tumours use more phenylalanine than others (particularly melatonin-producing tumours called melanomas). 63-91-2 6140 C9H11NO2 White powder. 283 dec°C 2.69E+004 mg/L (at 25°C) Absorbed from the small intestine by a sodium dependent active transport process. Extremely high serum levels of phenylalanine are found in patients with the inborn error of metabolism (IEM) called Phenylketonuria (PKU). At pathological concentrations typical of PKU, phenylalanine self-assembles into fibrils with amyloid-like morphology and well-ordered electron diffraction. These fibrils and their resulting amyloid deposits that localize to the brain appear to be partially responsible for the neural tissue damage seen in PKU patients (A8160). It has also been suggested that very high plasma phenylalanine concentrations can increase phenylalanine entry into brain and thereby restrict the entry of other large neutral amino acids. The lack of large neutral amino acids may lead to disturbed cerebral protein synthesis, which is particularly important for young children (A8162). The mechanism of L-phenylalanine's putative antidepressant activity may be accounted for by its precursor role in the synthesis of the neurotransmitters norepinephrine and dopamine. Elevated brain norepinephrine and dopamine levels are thought to be associated with antidepressant effects. <br/>The mechanism of L-phenylalanine's possible antivitiligo activity is not well understood. It is thought that L-phenylalanine may stimulate the production of melanin in the affected skin. Hepatic. L-phenylalanine that is not metabolized in the liver is distributed via the systemic circulation to the various tissues of the body, where it undergoes metabolic reactions similar to those that take place in the liver. No indication of carcinogenicity to humans (not listed by IARC). L-phenylalanine may be helpful in some with depression. It may also be useful in the treatment of vitiligo. There is some evidence that L-phenylalanine may exacerbate tardive dyskinesia in some schizophrenic patients and in some who have used neuroleptic drugs. Phenylalanine is neurotoxic. Chronic exposure to very high levels of phenylalanine in the blood (as found in phenylketonuria, or PKU) can lead to a build up in the cerebrospinal fluid and brain, leading to seizures, organ damage and unusual posture. High phenylalnine levels are particularly dangerous for children, because it retards brain development and can cause serious learning difficulties. Complications of PKU include severe intellectual disability, brain function abnormalities, microcephaly, mood disorders, irregular motor functioning, and behavioral problems such as attention deficit hyperactivity disorder. Chronically high levels of phenylalanine are associated with at least four other inborn errors of metabolism including: Hartnup Disorder, Hyperphenylalaniemia due to guanosine triphosphate cyclohydrolase deficiency, Tyrosinemia Type 2 (or Richner-Hanhart syndrome) and Tyrosinemia Type 3 (TYRO3). Complications of PKU include severe intellectual disability, brain function abnormalities, microcephaly, mood disorders, irregular motor functioning, and behavioral problems such as attention deficit hyperactivity disorder. If PKU is diagnosed early, an affected newborn can grow up with normal brain development, but only by managing and controlling phenylalanine levels through diet, or a combination of diet and medication. The diet requires severely restricting or eliminating foods high in phenylalanine, such as meat, chicken, fish, eggs, nuts, cheese, legumes, milk and other dairy products. Starchy foods, such as potatoes, bread, pasta, and corn, must be monitored. Optimal health ranges (or "target ranges") of serum phenylalanine are between 120 and 360 µmol/L, and aimed to be achieved during at least the first 10 years of life. Recently it has been found that a chiral isomer of L-phenylalanine (called D-phenylalanine) actually arrests the fibril formation by L-phenylalanine and gives rise to flakes. These flakes do not propagate further and prevent amyloid formation by L-phenylalanine. D-phenylalanine may qualify as a therapeutic molecule in phenylketonuria (A8161). 2014-08-29T06:35:23Z 2018-03-21T17:46:20Z L-Phenylalanine C00079 17295 PHE DB00120 PHE true [H][C@](N)(CC1=CC=CC=C1)C(O)=O C9H11NO2 InChI=1S/C9H11NO2/c10-8(9(11)12)6-7-4-2-1-3-5-7/h1-5,8H,6,10H2,(H,11,12)/t8-/m0/s1 InChIKey=COLNVLDHVKWLRT-QMMMGPOBSA-N 165.1891 165.078978601 Endogenous Solid -1.38 HMDB00159 CHEMBL301523 5910 <p>Gerald L. Bachman, &#8220;Recovery of L-phenylalanine and L-aspartic acid during preparation of .alpha.-L-aspartyl-L-phenylalanine methyl ester.&#8221; U.S. Patent US4348317, issued January, 1967.</p>