Transamination and its features

March 17, 2019

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.