Transamination is a chemical reaction that transfers an

amino group In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...

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 acids (amino acids that can be synthesized de novo by the organism). Transamination in biochemistry is accomplished by enzymes called

transaminase Transaminases or aminotransferases are enzymes that catalyze a transamination reaction between an amino acid and an α- keto acid. They are important in the synthesis of amino acids, which form proteins. Function and mechanism An amino acid ...

s or aminotransferases. α-ketoglutarate acts as the predominant amino-group acceptor and produces

glutamate Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can synt ...

as the new amino acid. :

Aminoacid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

+ α-ketoglutarate ↔ α-keto acid +

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

Glutamate Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can synt ...

+ oxaloacetate ↔ α-ketoglutarate +

aspartate Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. Like all other amino acids, it contains an amino group and a carboxylic acid. Its α-amino group is in the pro ...

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 Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from ...

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 Lys residue. The Schiff base, which is conjugated to the enzyme's pyridinium ring, is the focus of the coenzyme activity. : Picture2 aminotransferase

The product of transamination reactions depend on the availability of α-keto acids. The products usually are either

alanine Alanine (symbol Ala or A), or α-alanine, is an α-amino acid that is used in the biosynthesis of proteins. It contains an amine group and a carboxylic acid group, both attached to the central carbon atom which also carries a methyl group side ...

, since their corresponding alpha-keto acids are produced through metabolism of fuels. Being a major degradative aminoacid pathway,

lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. It contains an α-amino group (which is in the protonated form under biological conditions), an α-carboxylic acid group (which is in the deprotonated − ...

proline Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group but is rather a secondary amine. The secondary amine nitrogen is in the p ...

and

threonine Threonine (symbol Thr or T) is an amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), a carboxyl group (which is in the deprotonated −COO� ...

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. 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.^{/sup>

Types of aminotransferase

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

References

• Smith, M. B. and March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 5th ed. Wiley, 2001, p. 503.
• 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

Amino Acid Biosynthesis
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Organic reactions
Amino acids}