Editing Transamination (section)

==Mechanism of action==

Transamination catalyzed by aminotransferase occurs in two stages. In the first step, the α amino group of an amino acid is transferred to the enzyme, producing the corresponding α-keto acid and the aminated enzyme. During the second stage, the amino group is transferred to the keto acid acceptor, forming the amino acid product while regenerating the enzyme. The [[chirality (chemistry)|chirality]] of an amino acid is determined during transamination. For the reaction to complete, aminotransferases require participation of aldehyde containing coenzyme, '''pyridoxal-5'-phosphate (PLP)''', a derivative of Pyridoxine ('''[[Vitamin B6|Vitamin B<sub>6</sub>]]'''). The amino group is accommodated by conversion of this coenzyme to '''pyridoxamine-5'-phosphate (PMP). PLP''' is covalently attached to the enzyme via a Schiff Base linkage formed by the condensation of its aldehyde group with the ε-amino group of an enzymatic '''[[Lysine|Lys]]''' residue. The Schiff base, which is conjugated to the enzyme's pyridinium ring, is the focus of the coenzyme activity.

:[[File:Picture2 aminotransferase.jpg|centre|thumb|713x713px|Ping Pong Bi Bi mechanism of  PLP dependent enzyme catalyzed transamination. Aminotransferase reaction occurs in two stages consisting of three steps: Transimination, Tautomerisation and Hydolysis. In the first stage, alpha amino group of the aminoacid is transferred to PLP yielding an alpha ketoacid and PMP. In the second stage of the reaction, in which the amino group of PMP is transferred to a different alpha Ketoacid to yield a new alpha amino acid and PLP.]]The product of transamination reactions depend on the availability of α-keto acids. The products usually are either [[alanine]], [[aspartate]] or [[glutamate]], since their corresponding alpha-keto acids are produced through metabolism of fuels. Being a major degradative aminoacid pathway, [[lysine]], [[proline]] and [[threonine]] are the only three amino acids that do not always undergo transamination and rather use respective dehydrogenase.
:'''Alternative Mechanism'''
:A second type of transamination reaction can be described as a nucleophilic substitution of one amine or amide anion on an amine or ammonium salt.<ref name=":0">{{Cite book|publisher = Wiley-VCH Verlag GmbH & Co. KGaA|date = 2000-01-01|isbn = 9783527306732|doi = 10.1002/14356007.a17_009|first = Gerald|last = Booth|title = Ullmann's Encyclopedia of Industrial Chemistry|chapter = Naphthalene Derivatives}}</ref> For example, the attack of a primary amine by a primary amide anion can be used to prepare secondary amines:  
:RNH<sub>2</sub> + R'NH<sup>−</sup> → RR'NH + NH<sub>2</sub><sup>−</sup>  
:Symmetric secondary amines can be prepared using Raney nickel (2RNH<sub>2</sub> → R<sub>2</sub>NH + NH<sub>3</sub>). And finally, quaternary ammonium salts can be dealkylated using ethanolamine: 
:R<sub>4</sub>N<sup>+</sup> + NH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>OH → R<sub>3</sub>N + RN<sup>+</sup>H<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>OH  
:Aminonaphthalenes also undergo transaminations.<sup>[2]</sup>