Transamination

 ( Amino Acids ) 

Transamination is a chemical reaction that transfers an amino group.

In biochemistry, the processor occurs extensively during amino acid synthesis, catalyzed by transaminase, and requires a ketoacid. α-ketoglutarate acts as the predominant amino-group acceptor and produces glutamate.

Amino acid + α-ketoglutarate ↔ α-keto acid + Glutamic acid

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

Glutamic acid + oxaloacetate ↔ α-ketoglutarate + aspartate

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In biochemistry Transamination is responsible for the deamination of most amino acids, and one of the major degradation pathways which convert essential amino acids to non-essential amino acids (amino acids that can be synthesized de novo by the organism).

Transamination is mediated by several types of Transaminase 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 aminotransferase (ALT) and aspartate aminotransferase (AST).

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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 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). 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 residue. The Schiff base, which is conjugated to the enzyme's pyridinium ring, is the focus of the coenzyme activity.

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.

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Non-enzymatic transamination 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.Smith, M. B. and March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 5th ed. Wiley, 2001, p. 503. ISBN 0-471-58589-0 For example, the attack of a primary amine by a primary amide anion can be used to prepare secondary amines:

RNH₂ + R'NH⁻ → RR'NH + NH₂⁻

Symmetric secondary amines can be prepared using Raney nickel (2RNH₂ → R₂NH + NH₃). And finally, quaternary ammonium salts can be dealkylated using ethanolamine:

R₄N⁺ + NH₂CH₂CH₂OH → R₃N + RN⁺H₂CH₂CH₂OH

Aminonaphthalenes also undergo transaminations.

Gerald Booth (2000). 9783527306732, Wiley-VCH Verlag GmbH & Co. KGaA. ISBN 9783527306732

• Voet & Voet. Biochemistry, 4^th edition

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External links

• Amino Acid Biosynthesis
• The chemical logic behind aminoacid degradation and the urea cycle

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