- The chemical process in which there is transfer of an amino (-NH2) group from an amino acid to a keto-acid is known as transamination.
- This process involves the inter conversion of a pair of amino acids and a pair of keto acids which are catalyzed by a group of enzymes called transaminases (recently called aminotransferases).
Salient features of Transamination
- All transaminases require pyridoxal phosphate (PLP) which is a co-enzyme derived from vitamin B6.
- There are specific transaminases that exist for each pair of amino and keto acids. However, only two namely, aspartate transaminase and alanine transaminase make a significant contribution for transamination.
- There is no free NH3 liberated but only the transfer of a amino group occurs.
- Transamination is reversible.
- Transamination is very important for the re-distribution of amino groups and production of non-essential amino acids as per the requirement of the cell which involves both catabolism and anabolism of amino acids.
- Transamination helps to divert the excess amino acids towards energy generation.
- The amino acids undergo transamination so that it can finally concentrate nitrogen in glutamate.
- Glutamate is the only amino acid that undergoes oxidative deamination to a significant extent to liberate free NH3 that is used for urea synthesis.
- All amino acids participate in transamination (except lysine, threonine, proline and hydroxyproline).
- Transamination is not restricted to α-amino groups only. δ- amino group of ornithine is transaminated.
- Serum transaminases are important as they are used for diagnostic and prognostic purposes.
Mechanism of transamination
- Transamination occurs in two stages. They are as follows:
a)Transfer of the amino group to the co-enzyme pyridoxal phosphate (bound to the co-enzyme) to form pyridoxamine phosphate.
b)The amino group of pyridoxamine phosphate is then transferred to a keto acid to produce a new amino acid and the enzyme with PLP is regenerated.
- All the transaminases require pyridoxal phosphate (PLP), a derivative of vitamin B6.
- The aldehyde group of PLP is linked with ε- amino group of lysine residue, at the active site of the enzyme forming a Schiff base (imine linkage).
- When an amino acid (substrate) comes in contact with the enzyme, it displaces lysine and a new Schiff base linkage is formed.
- The amino acid-PLP-Schiff base tightly binds with the enzyme by non-covalent forces.
- Snell and Braustein proposed a Ping Pong Bi Bi mechanism involving a series of intermediates (aldimines and ketimines) in transamination reaction.
Transamination and its features