Deamination is the removal of an amino group from a molecule. Enzymes
that catalyse this reaction are called deaminases.
In the human body, deamination takes place primarily in the liver,
however glutamate is also deaminated in the kidneys. In situations of
excess protein intake, deamination is used to break down amino acids
for energy. The amino group is removed from the amino acid and
converted to ammonia. The rest of the amino acid is made up of mostly
carbon and hydrogen, and is recycled or oxidized for energy. Ammonia
is toxic to the human system, and enzymes convert it to urea or uric
acid by addition of carbon dioxide molecules (which is not considered
a deamination process) in the urea cycle, which also takes place in
Urea and uric acid can safely diffuse into the blood and
then be excreted in urine.
Deamination reactions in DNA
2 Additional proteins performing this function
3 See also
Deamination reactions in DNA
Spontaneous deamination is the hydrolysis reaction of cytosine into
uracil, releasing ammonia in the process. This can occur in vitro
through the use of bisulfite, which deaminates cytosine, but not
5-methylcytosine. This property has allowed researchers to sequence
DNA to distinguish non-methylated cytosine (shown up as
uracil) and methylated cytosine (unaltered).
In DNA, this spontaneous deamination is corrected for by the removal
of uracil (product of cytosine deamination and not part of DNA) by
DNA glycosylase, generating an abasic (AP) site. The resulting
abasic 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. A DNA
polymerase may perform this replacement via nick translation, a
terminal excision reaction by its 5'-->3' exonuclease activity,
followed by a fill-in reaction by its polymerase activity.
then forms a phosphodiester bond to seal the resulting nicked duplex
product, which now includes a new, correct cytosine. [See Base
Spontaneous deamination of
5-methylcytosine results in thymine 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 enzyme thymine-
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, like with uracil-DNA
Deamination of guanine results in the formation of xanthine. Xanthine,
in a manner analogous to the enol tautomer of guanine, selectively
base pairs with thymine instead of cytosine. This results in a
post-replicative transition mutation, where the original G-C base pair
transforms into an A-T base pair. Correction of this mutation involves
the use of alkyladenine glycosylase (Aag) during base excision repair.
Deamination of adenine results in the formation of hypoxanthine.
Hypoxanthine, in a manner analogous to the imine tautomer of adenine,
selectively base pairs with cytosine instead of thymine. This results
in a post-replicative transition mutation, where the original A-T base
pair transforms into a G-C base pair.
Additional proteins performing this function
APOBEC3G - affects HIV
Activation-induced (cytidine) deaminase (AICDA)
AMP deaminase (AMPD1)
Cytodine deaminase of mononucelotides (CDA)
Adenosine Deaminase acting on tRNA (ADAT)
Adenosine Deaminase acting on dsRNA (ADAR)
Adenosine Deaminase acting on mononucleotides (ADA)
Guanine Deaminase (GDA)
Adenosine monophosphate deaminase deficiency type 1
^ Gallinari, P. (1996). "Cloning and Expression of Human G/T
DNA Glycosylase". Journal of Biological
Chemistry. 271 (22): 12767–74. doi:10.1074/jbc.271.22.12767.