Deamination is the removal of anamino group from amolecule.^[1]Enzymes thatcatalyse this reaction are calleddeaminases.

In thehuman body, deamination takes place primarily in theliver; however, it can also occur in thekidney. In situations of excess protein intake, deamination is used to break downamino acids for energy. The amino group is removed from the amino acid and converted toammonia. The rest of the amino acid is made up of mostlycarbon andhydrogen, and is recycled or oxidized for energy. Ammonia is toxic to the human system, andenzymes convert it tourea oruric acid by addition ofcarbon dioxide molecules (which is not considered a deamination process) in theurea cycle, which also takes place in the liver. Urea and uric acid can safely diffuse into the blood and then be excreted in urine.

Spontaneous deamination is thehydrolysis reaction ofcytosine intouracil, releasingammonia in the process. This can occur in vitro through the use ofbisulfite, which deaminates cytosine, but not5-methylcytosine. This property has allowed researchers tosequencemethylated DNA to distinguish non-methylated cytosine (shown up asuracil) and methylated cytosine (unaltered).

InDNA, this spontaneous deamination is corrected for by the removal of uracil (product of cytosine deamination andnot part of DNA) byuracil-DNA glycosylase, generating an abasic (AP) site. The resultingabasic site is then recognised by enzymes (AP endonucleases) that break a phosphodiester bond in the DNA, permitting the repair of the resulting lesion by replacement with another cytosine. ADNA polymerase may perform this replacement vianick translation, a terminal excision reaction by its 5'⟶3' exonuclease activity, followed by a fill-in reaction by its polymerase activity. DNA ligase then forms a phosphodiester bond to seal the resulting nicked duplex product, which now includes a new, correct cytosine (Base excision repair).

Spontaneous deamination of5-methylcytosine results inthymine and ammonia. This is the most common single nucleotide mutation. In DNA, this reaction, if detected prior to passage of the replication fork, can be corrected by the enzymethymine-DNA glycosylase, which removes the thymine base in a G/T mismatch. This leaves an abasic site that is repaired by AP endonucleases and polymerase, as with uracil-DNA glycosylase.^[2]

A known result of cytosine methylation is the increase of C-to-T transition mutations through the process of deamination. Cytosine deamination can alter the genome's many regulatory functions; previously silencedtransposable elements (TEs) may become transcriptionally active due to the loss of CPG sites.^[3] TEs have been proposed to accelerate the mechanism of enhancer creation by providing extra DNA that is compatible with the host transcription factors that eventually have an impact on C-to-T mutations.^[3]

Deamination ofguanine results in the formation ofxanthine. Xanthine, however, still pairs withcytosine.^[4][5]

Deamination ofadenine results in the formation ofhypoxanthine. Hypoxanthine, in a manner analogous to the imine tautomer of adenine, selectively base pairs withcytosine instead ofthymine. This results in a post-replicative transition mutation, where the original A-T base pair transforms into a G-C base pair.

• APOBEC1
• APOBEC3A-H,APOBEC3G - affectsHIV
• Activation-induced cytidine deaminase (AICDA)
• Cytidine deaminase (CDA)
• dCMP deaminase (DCTD)
• AMP deaminase (AMPD1)
• Adenosine Deaminase acting on tRNA (ADAT)
• Adenosine Deaminase acting on dsRNA (ADAR)
  • Double-stranded RNA-specific editase 1 (ADARB1)
• Adenosine Deaminase acting on mononucleotides (ADA)
• Guanine Deaminase (GDA)

• Adenosine monophosphate deaminase deficiency type 1
• Hofmann elimination