Tyrosine is the amino acid with an aromatic side chain. It has hydroxyl group for H bonds and shows polarity. It is a non-essential amino acid which means it is synthesized in the body. It is glucogenic and ketogenic both.
In the foods, it is mainly found in those foods containing high protein content.
Animal sources include chicken, turkey, dairy products like yogurt, milk, cheese, and in fish.
The plant sources are almonds, peanuts, the seed of pumpkin, lime beans and sesame seeds etc.
Body tyrosine is mainly of dietary origin.
In our body tyrosine is produced from phenylalanine which is itself an amino acid. The reaction occurs in the presence of phenylalanine hydroxylase enzyme which is a mixed function oxidase that needs a tetrahydrobiopterine as a cofactor. This provides two hydrogens for the reaction and is then oxidized to dihydrobiopterine. The reaction also utilizes oxygen. Water is produced and the remaining ½ oxygen results in hydroxylation of phenylalanine at its para position forming a p-hydroxyphenylalanine which is also called tyrosine. The reaction also needs NADH+H+.
Tyrosine is known for giving lots of important products to our body. It gives rise to catecholamine e.g. adrenaline and noradrenalin and dopamine. They then function as neurotransmitters in our brain. These are important in maintaining the good balance of moods in person. If a deficiency occurs then this result in depression in a person. Dopamine further has another important physiological role in our body i.e. it stimulates the myocardial activity in the heart means it performs an isotropic action. Since it is a neurotransmitter in the brain, in case of its deficiency in the basal ganglia, an extrapyramidal disease called Parkinsonism occurs. It also acts as a prolactin release inhibiting factor in the anterior pituitary gland.
Tyrosine also helps in the production of tri-iodothyronine and tetraiodothyronine which are important thyroid gland hormones.
Tyrosine also takes part in melanin production. Melanin is the chief pigment of the skin and is also present in the eye, hairs and even brain in the substantia nigra.
Tyrosine also plays a role in enzyme receptors. Insulin receptor has been seemed to be a protein kinase which is tyrosine-specific. The hydroxyl group of tyrosine receives a phosphoryl group from ATP when insulin molecules become bound with the portion of receptor outside the cell.
The catabolism results in catabolic products of tyrosine which include homogentisic acid which is further broken down to fumaric acid and acetoacetic acid.
The defects in tyrosine metabolism lead to albinism which is a group of diseases as result of a deficiency in melanin. These result in either partial or full absence of pigments from the skin, eye, and hair. There may be vision defects and photophobia. This disease occurs due to deficiency of tyrosinase enzyme.
Alkaptonuria is another disease due to deficiency of homogentisic acid oxidase that results in accumulation of homogentisic acid. A patient may have homogenetic aciduria, arthritis of large joints, and black pigmentation of cartilage and collagenous tissues.
Tyrosine interacts with monoamine oxidase inhibitors so a patient should avoid foods containing tyrosine.
Thus, tyrosine has many beneficial effects. It supplementation is also available for the persons deficient of this amino acid. It is a useful amino acid during periods of cold, stress of any kind either emotional or physical and fatigues.