Proteins are bio polymers of amino acids. In the formation of proteins, two molecules of amino acids bonded through a peptide bond( C(=O)NH-) between carboxyl group of one molecule and amino group of the other molecule through the elimination of a molecule of water (H2O). The combination of two amino acids form dipeptides which can further bonded with other amino acids to form polypeptide chains. Thus polypeptides and proteins are chains of amino acids bonded together by peptide bonds and form backbone of proteins.
Protein sequences have one free end consist -NH3+ group called as the N terminus and another end with the free -COO- group known as the C terminus. For example, three amino acids asparagine, threonine and arginine bonded with peptide bonds to form tripeptide written as Asn-Thr-Arg. The N-terminus is written on left side and C-terminus on right side.
Alpha amino acids are also called as proteinogenic amino acids which mean "protein building capacity"
as only alpha amino acids can involve in protein formation. There are 22 amino acids; out of that 21 are present in eukaryotes
Twenty amino acids are encoded by universal genetic code. There are total 10 amino acids which can be synthesized in human body from other molecules of intermediary metabolism and called as non-essential amino acids. Rest of ten amino acids are essential amino acids as they cannot synthesize in human body and must be consumed (usually as their protein derivatives) in the diet.
Tyrosine is an aromatic, non-polar, hydrophobic, essential amino acid with hydroxy group on phenyl ring in side chain. Tyrosine is considered as a hydroxyl derivative of phenylalanine at para position and more soluble that is phenylalanine. The molecular formula of tyrosine is C9H11NO3 with molecular mass 181.19 g mol-1.
The major food sources of tyrosine are dairy products like one cup of cottage cheese contains 1,495mg of tyrosine, legumes like one cup of baked legumes contains 395mg of tyrosine, one cup of brown rice, which has 190mg of tyrosine, and chicken (6 oz. of chicken breast with no skin contains 950mg of tyrosine).
Like other aromatic amino acids; tryptophan and phenylalanine, tyrosine can also synthesized from chorismate. Two biochemical compounds phosphoenol pyruvate
and erythrose 4-phosphate
are act as precursor for chorismate which further converts in tyrosine amino acid.
Prephenate, an intermediate on the shikimate pathway acts as precursor of tyrosine in many plant and organism. While phenylalanine acts as precursor for tyrosine in mammals which form tyrosine in the presence of enzyme phenylalanine hydroxylase which is a mixed-function oxygenase.
- L-tyrosine involve in the production of adrenaline and several neurotransmitters and is considered by some to be a mood elevator and able to fight depression.
- It is also acts as an antioxidant and used to suppress appetite, stress reduction, to combat anxiety, depression, allergies, and headaches.
- Tyrosine is able to increase energy and enhance libido which show a positive effect on several health conditions, like Parkinson's disease and Alzheimer's.
- This amino acid also increases the production of thyroid hormones in the body which further increase the rate of metabolism by raising body temperature to normal levels.
- The high metabolic rate results the weight loss and it play an intricate part in raising metabolism due to the fact that it raises the production of thyroid hormones, which are responsible for increase metabolic rate.
The IUPAC name of tyrosine is 2-Amino-3-(4-hydroxyphenyl) propanoic acid which contains one amino group, one carboxyl group with one phenyl ring as side chain. Phenyl ring contains one hydroxyl group at para position.
Tyrosine is an example of aromatic amino acids with phenolic group on side chain. The hydroxyl group of tyrosine is more acidic compare to other aliphatic hydroxyl groups of other amino acids like serine or Threonine. The phenolic hydroxyl of tyrosine is significantly more acidic than other aliphatic hydroxylase groups of aliphatic amino acids with hydroxyl group like serine or threonine. The zwitterion of tyrosine is overall non-charged molecule due to non-polar side chain in which R group is a methylene group bonded to a benzene ring with an OH in the para position.
- The isoelectric point of tyrosine is at pH 5.66, as the pKa1 2.20(Î±-carboxyl group) and pKa2 9.11 (Î±-ammonium ion), hence the isoelectric point (pI) will be Â½(
- As with all ionizable groups in amino acid molecule, the precise pKa will depend to upon the environment of amino acid within the protein.
Tyrosines is orientated on the surface of proteins due to lower pKa
, those amino acid molecule which are buried within a protein have high value of pKa, ionization form of phenolic group that is the phenolate anion would be unstable in the hydrophobic interior of a protein Like other alpha amino acids; tyrosine also shows D and L configurations, out of which L-configuration is more common and mainly involve in protein synthesis.