What Is Transamination

Transamination

Transamination  the degradation of dietary and body protein yield amino acid  they are deaminated early in catabolism and then nitrogen and carbon skeleton are processed independently .the carbon skeleton of amino acid can have multiple fates depending on the requirement .some of these fates include complete oxidation  via TCA cycle to provide energy ;glucose synthesis (gluconeogenesis); synthesis of lipid ,fatty acid and ketone bodies and synthesis of non essential amino acid.

the a-amino group of most acids is removed by amino transferases or transaminases. these enzyme mediate the transfer of amino group of an amino acid to a keto acid .during the process there is no net deamination . all transaminases are pyridoxal phosphate dependent enzyme through an aldimine linkage(schiff 's base )the keto acceptor of the amino group in majority of amino acids is a-ketoglutarate thereby generating glutamate as one of the product .some amino acids (histidine, serine, threonine arginine ,proline ,amide nitrogen of glutamine and asparagine ) do not undergo transamination. these amino acids are directly deaminated by specific enzymes about which you will learn in the next unit.

the formation of glutamate allows the cell to either utilize it is an amino donor in biosynthesis or for oxidation deamination of the amino groups collected from different amino acids primarily by glutamate dehydrogenase (GDH) and to some extent by L- amino acid oxidases .it goes without saying that cell do not need separate enzyme for deamination of each amino acid. the sequential action of the transamination and GDP is termed transdeamination finally ammonia is detoxified into urea cycle and excreted.

In Eukaryotes a number of transaminases are required for funneling nitrogen into glutamine. they differ specificity for the amino donor and are named accordingly such as aspartate amino transferase and alanine amino transferase. almost every cell has amino transaminases both in the cytosol and mitochondria. some salient features of transaminases are:

The coenzyme shuttle reversibly between the aldehyde (pyridoxal phosphate) and its redused aminated from (pyridoxamine phosphate)

Aspartate and alanine transaminase make significant contribution to overall transamination.

Transamination reaction are freely reversible.

Transamination reaction is involved in both catabolism and anabolism amino acids. 

These reaction are involved in synthesis of non -essential amino acid.

Transamination concentrates nitrogen from different amino acids into glutamate.

Besides a-amino acids, some b-amino acids such as ornithine also undergo transamination.

serum transaminase such as aspartate transaminase (AST)and alanine transaminase (AST) are important prognostic and diagnostic biomarkers

mechanism of transamination

A transamination reaction occurs by ping pong Bi Bi mechanism in which the first product leaves the active site before the before the second substrate binds (for details , refer to bbcct107 .in ping pong (double displacement)mechanism the enzyme change into an intermediate (temporary)from when the first substrate to product reaction occurs .this mechanism was proposed by E.snell, A.braunstein and d. metzler. 

The basic reaction proceeds in the stages. in two stages. in two stages. in the first stages(the amino acid binds to the active site and  forms  a new aldimine linkage between the substrate and pyridoxal  phosphate (external aldimine )this is followed by proton abstraction (from donor amino acid ),producing pyridoxamine phosphate (of PLP) and hydrolsis of the resultant ketimine producing pyridoxamine phosphate and the first product leaves as a- ketoacid.

the second substrate now bind to the enzyme and forms a ketimine with the amino group of pyridoxamine phosphate .these steps are a reversal of stage. there is removal of proton .protonation of ketoacid and hydrolysis to release the amino acid with regeneration of PLP.