phenylalanine


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Related to phenylalanine: Phenylalanine hydroxylase

phenylalanine

(fĕn'əlăl`ənēn'), organic compound, one of the 22 α-amino acidsamino acid
, any one of a class of simple organic compounds containing carbon, hydrogen, oxygen, nitrogen, and in certain cases sulfur. These compounds are the building blocks of proteins.
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 commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein. It is one of several essential amino acids needed in the diet; human beings cannot synthesize it from simpler metabolites. Young adults need about 31 mg of this amino acid per day per kg (14 mg per lb) of body weight. Phenylalanine can be degraded into simpler compounds by the enzymes of the body and is readily converted to the amino acid tyrosinetyrosine
, organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein.
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. Phenylketonuriaphenylketonuria
(PKU), inherited metabolic disorder caused by a deficiency in a specific enzyme (phenylalanine hydroxylase). The absence of this enzyme, a recessive trait, prevents the body from making use of phenylalanine, one of the amino acids in most protein-rich foods, and
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 (PKU), an inherited disease that, if left untreated, results in retarded mental development in children, has been shown to be associated with the lack of activity of the enzyme that converts phenylalanine to tyrosine. This results in the buildup of phenylalanine in the blood, an event leading to several pathological consequences. The incidence of this disease, about one in every 10,000 births, is high enough to have prompted several states to institute regular screening procedures for the detection of the disease in newborns. If diagnosed early the disease can be controlled to a great extent by administering a diet very low in phenylalanine. Phenylalanine contributes to the structure of proteins into which it has been incorporated by the tendency of its side chain to participate in hydrophobic interactions (see isoleucineisoleucine
, organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein.
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). This amino acid was first isolated from a natural source (lupine sprouts) in 1879; it was first chemically synthesized in 1882.

Phenylalanine

 

(also alpha-amino-beta-phenylpropionic acid), C6H5CH2CH(NH2)COOH, an aromatic amino acid. Phenylalanine exists in dextrorotatory (D), levorotatory (L), and racemic (DL) forms. In its L form, the amino acid is present (3–8 percent) in all natural proteins except protamines, and it occurs in the free state in animals, plants, and microorganisms. L-phenylalanine is an essential amino acid, the daily requirement of which is 4.3 mg/kg for adult males, 3.1 mg/kg for adult females, and 90 mg/kg for children. It is continuously formed in the body from the breakdown of proteins derived from food and tissue proteins. The need for phenylalanine increases in the absence of the amino acid tyrosine in food; tyrosine is normally formed in the liver by the hydroxylation of phenylalanine with the participation of the enzyme phenylalanine hydroxylase. The disruption of this process through a genetically caused defect leads to the accumulation of phenylalanine in the body cells and fluids. Disruption of the normal pathway for the conversion of phenylalanine produces secondary biochemical reactions (Figure 1) that lead to the formation of phenylpyruvic, phenyllactic, and phenylacetic acids in the body and to the development of a disease known as phenylketonuria.

Figure 1. Pathways for the metabolism of phenylalanine in humans

In normal metabolism, phenylalanine is converted through tyrosine to dihydroxyphenylalanine, melanins, norepinephrine, and adrenaline; to a slight extent, it undergoes transamination. The direct precursor in the biosynthesis of phenylalanine in plants and microorganisms is phenylpyruvic acid, the aromatic ring of which is synthesized in a complex sequence of enzyme-catalyzed reactions from phosphophenylpyruvic acid and D-erythrose-4-phosphate by way of shikimic acid. In the breakdown of L-phenylalanine in the body, eight of the nine carbon atoms are introduced into the tricarboxylic acid cycle in the form of acetyl coenzyme A and fumarate; one carbon atom is converted into CO2. In the decomposition of proteins, especially in the intestines of animals and humans, phenylalanine is converted into the biogenic amine phenethylamine.

REFERENCES

Meister, A. Biokhimiia aminokislot. Moscow, 1961. (Translated from English.)
Harris, H. Osnovy biokhimicheskoi genetiki cheloveka. Moscow, 1973. (Translated from English.)

E. N. SAFONOVA

phenylalanine

[¦fen·əl′al·ə‚nēn]
(biochemistry)
C9H11O2N An essential amino acid, obtained in the levo form by hydrolysis of proteins (as lactalbumin); converted to tyrosine in the normal body. Also known as α-aminohydrocinnamic acid; α-amino-β-phenylpropionic acid; β-phenylalanine.
References in periodicals archive ?
As phenylalanine builds up in the blood, it can damage neurons in the brain, leading to delayed development, intellectual disability and psychiatric disorders.
High levels of free amino acids correlate with high water-holding capacity of stratum corneum.19 We observed that 90% of studied amino acids (asparagine, glutamine, phenylalanine, and tyrosine) were in higher level in infected people compared to healthy individuals (Figure 1).
Testing for tetrahydrobiopterin responsiveness in patients with hyperphenylalaninemia due to phenylalanine hydroxylase deficiency.
According to the growth performance, hemolymph samples from groups P1, P4, and P6 were chosen to detect metabolites by GC/MS because these three groups represented for deficiency of, near-optimal, and excessive dietary phenylalanine supplementary.
Contraindications: Though, with careful dosing, these two aminos seldom cause actual problems for our clients, there are more possible contraindications to the use of tyrosine and phenylalanine (e.g.
Since phenylalanine is found in many foods such as chicken, meat, eggs, dairy, nuts, grains, and legumes, people with PKU typically must eat a special diet.
Skeletal muscle growth and loss were significantly related to baseline phenylalanine levels (Supplementary Figure IIB) and weakly related to BNP (r = -0.39, p <0.001).
The study shows how phenylalanine reduces food intake by affecting the gut and the brain, and suggests that it may be used to prevent or treat obesity.
Depending on the degree of enzyme deficiency, disease can be divided in several forms: Classical phenylketonuria - the most severe, with the highest deficit of phenylalanine hydroxylase enzyme and phenylalanine concentration greater than 20 mg/dL (Phe > 1,200 mmol/L).
Double blind placebo control trial of large neutral amino acids in treatment of PKU: effect on blood phenylalanine. J Inherit Metab Dis 2007; 30:153-58.
The Phenylalanine Hydroxylase (PAH) gene, being 90-100 kb, is embedded in the genomic location 102, 836, 885-102, 958, 410, on the chromosomal region 12q23.2 (1).
PKU is looked for in all UK newborns today by measuring phenylalanine levels in the heelprick blood test.

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