Phenylalanine is the amino acid with the aromatic side chain and is relatively polar. It is one of the essential amino acids which means it should be provided to the body from diet.
This amino acid also absorbs ultraviolet light and strong a absorbance of light by protein is at 280 nm. This property is used to detect and measure proteins. Its codons are UUU and UUC and are coded for by DNA as well. The codons are discovered by Heinrich Matthaei and Marshall Nirenberg in 1961. It has three forms: D-phenylalanine, L-phenylalanine, DL-phenylalanine.
It is mostly found in protein-rich foods.
Animal sources: Fish, poultry, dairy foods, cheese, yogurt, beef etc
Plant sources: They contain avocado, almonds, lima beans, seeds peanuts, nuts, and tofu etc.
It is also present in the breast milk of some mammals.
Phenylalanine supplements are also available.
Phenylalanine gives rise to tyrosine which is one of the most important amino acids. This reaction is characterized by phenylalanine hydroxylase.
Tyrosine also gives rise to many different and essential products, for example, melanin, thyroid gland, and neurotransmitters like aldosterone, noraldosterone, and dopamine. So it is also involved in the central nervous system.
This amino acid has been seen to improve Parkinsonism symptoms such as walking difficulties, rigidity, difficulties in speech etc.
Phenylalanine crosses the blood-brain barrier and then it interferes with the formation of serotonin.
D-phenylalanine plays an important role in the treatment and relief of chronic pains.
It has also found useful in persons with vitiligo as it helps to strengthen the ultraviolet rays’ effect on them.
It may also be helpful in case of depression as it gives rise to tyrosine which produces neurotransmitters essential for depression removal.
This amino acid is converted into many derivatives that are excreted in the urine. These are phenyl acetic acid, phenyllactic acid, hydroxyphenylpyruvic acid and hydroxyphenylacetic acid. However, this is the normal pathway of this amino acid and it becomes quantitively more important when phenylalanine does not undergo in its major pathway which is its conversion to tyrosine.
Phenylketonuria is the disease of an inborn error of amino acid metabolism. This disease is caused by a deficiency of phenylalanine hydroxylase. Symptoms of the central nervous system arise which include seizures, failure to walk and talk, microcephaly, hyperactivity and failure to grow. Hypopigmentation also occurs in this disease.
Early diagnosis of phenylketonuria is important because it is possible to treat early by means of diet. Neonatal and antenatal screening is possible.
Treatment includes lifelong phenylalanine-restricted diets.
When women suffering from this disease and not on restricted diet become pregnant, her offsprings are then affected with maternal phenylalanine syndrome. The high level of this amino acid causes mental retardation, microcephaly and congenital heart diseases in the baby. So its level should be controlled prior to conception.
Phenylalanine thus is a very important amino acid. Nowadays it has been used to produce certain medicines and nutritional supplements synthetically.