Deamination

Deamination is a biochemical process that involves the removal of an amine group from a molecule. It plays a crucial role in the metabolism of amino acids and the production and elimination of waste nitrogen compounds in humans and other organisms.

File:Deamination

In the broadest sense, deamination is the process wherein an amine group is detached from a molecule. This reaction is facilitated by enzymes known as deaminases.

Physiology of Deamination

In Humans

The human body primarily conducts deamination in the liver. An exception is the deamination of glutamate, which occurs in the kidneys. This process becomes pivotal when there's an overconsumption of protein. The amino acid's amino group is detached and converted into ammonia. The residual part of the amino acid, primarily composed of carbon and hydrogen, either gets recycled or oxidized to produce energy.

However, ammonia is toxic to humans, and the body has mechanisms to counteract its harmful effects. In the liver, through the urea cycle, ammonia gets transformed into urea or uric acid with the aid of carbon dioxide molecules. This transformation doesn't fall under deamination. The produced urea and uric acid are then harmlessly diffused into the bloodstream and eventually eliminated via urine.

Spontaneous Deamination

Spontaneous deamination can lead to the conversion of cytosine into uracil, releasing ammonia. This reaction can be artificially induced using bisulfite. Notably, bisulfite alters cytosine but leaves 5-methylcytosine untouched, providing a methodology for DNA sequencing to differentiate between methylated and non-methylated cytosine.

Within DNA, spontaneous deamination's repercussions are nullified by uracil-DNA glycosylase, which removes the "alien" uracil. This creates an abasic site, which is subsequently addressed and repaired by various enzymes and processes, ultimately restoring the correct cytosine. Base excision repair is one such pivotal repair mechanism.

Specific Deamination Reactions

5-methylcytosine

When 5-methylcytosine undergoes spontaneous deamination, it produces thymine. This is the predominant single nucleotide mutation. Enzymes like thymine-DNA glycosylase can rectify this prior to replication.

Guanine

Deamination transforms guanine into xanthine. Xanthine tends to pair with thymine, resulting in a mutation. Alkyladenine glycosylase (Aag) is involved in the corrective process during base excision repair.

Adenine

Adenine's deamination produces hypoxanthine, which selectively pairs with cytosine, leading to a mutation.

Additional Proteins Involved in Deamination

• APOBEC3G - Notably impacts HIV.
• Apolipoprotein B

See Also

• Amine
• Enzymes
• Urea cycle
• DNA repair

References

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