Deamination

As deamination refers to the chemical removal of an amino group as ammonium ion or ammonia . Deamination takes place both in biochemistry and in chemical-technical processes. A distinction is made between oxidative, hydrolytic and eliminative deamination.

Deamination is the first step in the biochemical breakdown of amino acids . In mammals , this process takes place mainly in the liver . The ammonium ion formed is then converted into urea in order to prevent the cell-toxic effect of the conjugate base ammonia .

Oxidative (dehydrogenative) deamination

In the first step of the oxidative deamination, the amino group of the amino acid L - glutamate 1 is oxidized to the imino group by splitting off hydrogen , the hydrogen being transferred to NAD ⁺ or NADP ⁺ . This is followed by hydrolytic cleavage of the imino group as ammonium ion and the formation of an α- keto acid , α-ketoglutarate 2 :

Also FMN and FAD catalyzing redox reactions, including oxidative deamination. In contrast to soluble NAD ⁺ or NADP ⁺ , they are bound to their enzyme as a prosthetic group and have to be regenerated there too.

Hydrolytic deamination

Here, ammonia (NH ₃ ) is hydrolytically split off from the acid amide group of an amino acid. The amide group is split off by water retention and replaced by an OH group. Correspondingly, acid amides result in carboxylic acids (COOH group).

Further utilization of the released ammonia

The ammonia released during the deamination of amino acids is a cell poison and must therefore be bound or excreted. On the one hand, it can be bound to alpha-keto acids, which then become amino acids, or it is excreted in the urine. The latter occurs in the human body mainly through the synthesis of urea in the urea cycle , which takes place in the liver . The urea is then released into the blood and excreted in the urine via the kidneys . The kidneys also have a mechanism that leads to the direct excretion of ammonia in the urine. The simultaneous transport of ammonia (NH ₃ ) and protons (H ⁺ ) in the kidney tubules causes them to combine to form an ammonium ion (NH ₄ ⁺ ). Ammonium can no longer cross the membrane of the kidney cells and is excreted in the urine. (However, this is primarily used to regulate the acid-base balance, because this is how protons are removed from the body, which is important when compensating for acidosis.)

See also

• Amination
• Transamination
• Glutamate dehydrogenase
• AMP deaminase
• Myoadenylate deaminase deficiency

literature

• Jeremy M. Berg, John L. Tymoczko, Lubert Stryer : Biochemistry. 6 edition, Spektrum Akademischer Verlag, Heidelberg 2007. ISBN 978-3-8274-1800-5 .
• Donald Voet, Judith G. Voet: Biochemistry. 3rd edition, John Wiley & Sons, New York 2004. ISBN 0-471-19350-X .
• Bruce Alberts , Alexander Johnson, Peter Walter, Julian Lewis, Martin Raff, Keith Roberts: Molecular Biology of the Cell , 5th Edition, Taylor & Francis 2007, ISBN 978-0815341062 .

Individual evidence

1. ^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, p. 276.