Editing Transamination

{{Short description|Chemical reaction that transfers an amino group to a ketoacid}}
[[File:Transaminierung.svg|thumb|right|300px|Aminotransfer reaction between an [[amino acid]] and an alpha-keto acid]]

'''Transamination''' is a chemical reaction that transfers an [[amino group]] to a [[ketoacid]] to form new amino acids.This pathway is responsible for the deamination of most amino acids. This is one of the major degradation pathways which convert [[essential amino acids]] to [[non-essential amino acid]]s (amino acids that can be synthesized de novo by the organism).

Transamination in biochemistry is accomplished by enzymes called [[transaminase]]s or aminotransferases. [[α-ketoglutarate]] acts as the predominant amino-group acceptor and produces [[glutamate]] as the new amino acid.

:[[Amino acid|Aminoacid]]  + α-ketoglutarate ↔ α-keto acid  + [[Glutamic acid|glutamate]]

Glutamate's amino group, in turn, is transferred to oxaloacetate in a second transamination reaction yielding aspartate.

:[[Glutamic acid|Glutamate]]  +  oxaloacetate  ↔  α-ketoglutarate + [[aspartate]]

==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>

==Types of aminotransferase==

Transamination is mediated by several types of [[Transaminase|aminotransferase]] enzymes. An aminotransferase may be specific for an individual amino acid, or it may be able to process any member of a group of similar ones, for example the branched-chain amino acids, which comprises valine, isoleucine, and leucine. The  two common types of aminotransferases are [[Alanine transaminase|alanine aminotransferase (ALT)]] and [[Aspartate transaminase|aspartate aminotransferase (AST)]].

==References==
{{Reflist}}
•  Smith, M. B. and March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 5th ed. Wiley, 2001, p.&nbsp;503. {{ISBN|0-471-58589-0}} 
•  Gerald Booth "Naphthalene Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a17_009

Voet & Voet. "Biochemistry" Fourth edition

==External links==
* [http://homepages.rpi.edu/~bellos/new_page_2.htm Amino Acid Biosynthesis] {{Webarchive|url=https://web.archive.org/web/20170426224825/http://homepages.rpi.edu/~bellos/new_page_2.htm |date=2017-04-26 }} 
* [https://web.archive.org/web/20141216152126/http://www2.ufp.pt/~pedros/bq/urea.htm The chemical logic behind aminoacid degradation and the urea cycle]

[[Category:Amino acids]]
[[Category:Biochemical reactions]]
[[Category:Organic reactions]]