Transamination
Transamination (or aminotransfer) is a chemical reaction between two molecules. One is an amino acid, which contains an amine (NH2) group. The other is a keto acid, which contains a keto (=O) group. In transamination, the NH2 group on one molecule is exchanged with the =O group on the other molecule. The amino acid becomes a keto acid, and the keto acid becomes an amino acid.
Transamination in biochemistry is accomplished by enzymes called transaminases or aminotransferases. This process is an important step in the synthesis of some non-essential amino acids (amino acids that can be synthesized de novo by the organism). The chirality of an amino acid is determined during transamination. This reaction uses the coenzyme PLP, and has been shown to be a kinetically perfect reaction. The product of transamination reactions depend on the availability of alpha-keto acids. The products usually are either alanine, aspartate or glutamate, since their corresponding alpha-keto acids are produced through metabolism of fuels.
Lysine and threonine are the only two amino acids that do not always undergo transamination and rather use serine or threonine dehydrogenase.
The second type of transamination reaction can be described as a nucleophilic substitution of one amine or amide anion on an amine or ammonium salt.[1] 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
References
- ↑ Smith, M. B. and March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 5th ed. Wiley, 2001, p. 503. ISBN 0-471-58589-0
External links
- Overview of amino acid synthesis (dead link)
- The chemical logic behind aminoacid degradation and the urea cycle