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'''Monoamine oxidases''' (singular abbreviation '''MAO''') ({{EC number|1.4.3.4}}) are [[enzyme]]s that [[catalysis|catalyze]] the [[oxidation]] of [[monoamine]]s. They are found bound to the outer membrane of [[mitochondria]] in most cell types in the body.
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'''Monoamine oxidases''' (singular abbreviation '''MAO''') ({{EC number|1.4.3.4}}) are [[enzyme]]s that [[catalysis|catalyze]] the [[oxidation]] of [[monoamine]]s. They are found bound to the outer membrane of [[mitochondria]] in most cell types in the body. The enzyme was discovered by Mary Hare in the [[liver]], and received the name of tyramine oxidase.<ref>Hare MLC (1928) Tyramine oxidase. I. A new enzyme system in liver. Biochem J 22:968Y979 </ref> They belong to [[protein family]] of [[flavin containing amine oxidoreductase]]s.
 
There are two types of MAO: MAO-A and MAO-B. Both are found in [[neuron]]s and [[astroglia]]; MAO-A is also found in the [[liver]], [[gastrointestinal tract]] and [[placenta]]. Outside the [[central nervous system]], MAO-B is mostly found in [[blood]] [[platelet]]s.
 
   
  +
==Locations of MAO-A and MAO-B==
  +
In humans there are two types of MAO: [[Monoamine oxidase A|MAO-A]] and [[MAOB|MAO-B]].
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* Both are found in [[neuron]]s and [[astroglia]].
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* Outside the [[central nervous system]]:
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** MAO-A is also found in the [[liver]], [[gastrointestinal tract]] and [[placenta]].
  +
** MAO-B is mostly found in [[blood]] [[platelet]]s.
   
 
==Function==
 
==Function==
Monoamine oxidases catalyze the oxidative [[deamination]] of monoamines. [[Oxygen]] is used to remove an [[amine]] group from a molecule, resulting in the corresponding [[aldehyde]] and [[ammonia]]. The general form of the catalized reaction (with R denoting an arbitrary group) is
+
Monoamine oxidases catalyze the [[oxidative deamination]] of monoamines. [[Oxygen]] is used to remove an [[amine]] group from a molecule, resulting in the corresponding [[aldehyde]] and [[ammonia]]. The general form of the catalyzed reaction (with R denoting an arbitrary group) is
   
 
H H
 
H H
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H
 
H
   
Monoamine oxidase contains the covalently-bound [[cofactor]] [[FAD]].
+
Monoamine [[oxidase]]s contain the covalently-bound [[cofactor (biochemistry)|cofactor]] [[FAD]] and are thus classified as [[flavoprotein]]s.
 
   
 
==Subtype Specificities==
 
==Subtype Specificities==
MAO-A is particularly important in the catabolism of monoamines ingested in food. Both MAOs are also vital to the inactivation of monoaminergic [[neurotransmitter]]s, for which they display different [[Enzyme#Specificity|specificities]]. Thus, [[serotonin]] is mainly broken down by MAO-A, as is [[norepinephrine]] (noradrenaline) and [[epinephrine]] (adrenaline), while [[phenethylamine]] is broken down by MAO-B. Both forms break down [[dopamine]].
+
MAO-A is particularly important in the catabolism of monoamines ingested in food. Both MAOs are also vital to the inactivation of monoaminergic [[neurotransmitter]]s, for which they display different [[Enzyme#Specificity|specificities]].
   
  +
* [[Serotonin]], [[norepinephrine]] (noradrenaline), and [[epinephrine]] (adrenaline) are mainly broken down by MAO-A.
Genetic, high levels of MAOA have been reported (Caspi et al, 2002) to provide protection from the detrimental effects of being maltreated as childen.
 
  +
* [[Phenethylamine]] is broken down by MAO-B.
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* Both forms break down [[dopamine]].
   
 
==Disorders resulting from MAO dysfunction==
Brain imaging studies by Meyer-Lindenberg et al (2006)found that men who had a genotype leading to low expression of MAOA (now identified as a risk factor for violent behavior)showed reduced functioning in thei [[anterior cingulate cortex]] when they tried to inhibit a physical response, and exaggerated [[amygdala]] funtioning suggestive of heightened anxiety and fearfulness
 
 
Because of the vital role that MAOs play in the inactivation of neurotransmitters, MAO dysfunction (too much/too little MAO activity) is thought to be responsible for a number of neurological disorders. For example, unusually high or low levels of MAOs in the body have been associated with [[clinical depression|depression]], [[substance abuse]], [[attention deficit disorder]], and irregular sexual maturation. [[Monoamine oxidase inhibitor]]s are one of the major classes of drug prescribed for the treatment of depression, although they are last line treatment due to risk of the drug's interaction with diet or other drugs. Excessive levels of [[catecholamine]]s ([[epinephrine]], [[norepinephrine]], and [[dopamine]]) may lead to a hypertensive crisis, and excessive levels of [[serotonin]] may lead to [[serotonin syndrome]].
  +
  +
[[Positron emission tomography|PET]] research has shown that MAO is also heavily depleted by use of [[tobacco]] cigarettes.<ref>{{cite journal |author=Fowler JS, Volkow ND, Wang GJ, Pappas N, Logan J, MacGregor R, Alexoff D, Wolf AP, Warner D, Cilento R, Zezulkova I |title=Neuropharmacological actions of cigarette smoke: brain monoamine oxidase B (MAO B) inhibition. |journal=Journal of addictive diseases |year=1998 |pmid=9549600}}</ref>
   
 
==Genetics==
 
==Genetics==
The [[gene]]s encoding MAO-A and MAO-B are both located on the short arm of the [[X chromosome]]. These two genes are to be found side-by-side, and have about 70% homology.
 
   
 
The [[gene]]s encoding MAO-A and MAO-B are located side-by-side on the short arm of the [[X chromosome]], and have about 70% sequence similarity. Rare mutations in the gene are associated with [[Brunner syndrome]].
   
  +
A study reported in ''[[Science (journal)|Science]]'' in August 2002 concluded that maltreated children with a low-activity polymorphism in the [[promoter]] region of the MAO-A gene were more likely to develop [[conduct disorder|antisocial conduct disorders]] than maltreated children with the high-activity variant.<ref>{{cite journal |author=Caspi A, McClay J, Moffitt T, Mill J, Martin J, Craig I, Taylor A, Poulton R |title=Role of genotype in the cycle of violence in maltreated children |journal=Science |volume=297 |issue=5582 |pages=851-4 |year=2002 |pmid=12161658}}</ref> The suggested mechanism for this effect is the decreased ability of those with low MAO-A activity to quickly degrade norepinephrine, the synaptic neurotransmitter involved in [[sympathetic nervous system|sympathetic]] arousal and rage. This is alleged to provide direct support for the idea that genetic susceptibility to disease is not determined at birth, but varies with exposure to environmental influences.
==Disorders resulting from MAO dysfunction==
 
   
  +
Research also uncovered a possible link between predisposition to [[neophilia|novelty seeking]] and a [[genotype]] of the MAO-A gene.<ref>[http://www.medialifemagazine.com/cgi-bin/artman/exec/view.cgi?archive=226&num=5439 The disorder of these times, neophilia], by Heidi Dawley, published June 18, 2006, retrieved on May 22, 2007</ref>
Because of the vital role that MAOs play in the inactivation of neurotransmitters, MAO dysfunction (too much/too little MAO activity) is thought to be responsible for a number of neurological disorders. For example, unusually high or low levels of MAOs in the body have been associated with [[clinical depression|depression]], [[substance abuse]], [[criminality]], [[attention deficit disorder]], and social [[phobias]]. [[Monoamine oxidase inhibitor]]s are one of the major classes of drug prescribed for the treatment of depression.
 
  +
 
  +
In 2006, a New Zealand researcher, Dr Rod Lea said that a particular variant (or [[genotype]]) was over-represented in [[Māori]], a [[Warrior gene]]. This supported earlier studies finding different proportions of variants in different ethnic groups. This is the case for many genetic variants, with 33% White/Non-Hispanic, 61% Asian/Pacific Islanders having the low-activity MAO-A [[promoter]] variant.<ref>{{cite journal |author=Sabol S, Hu S, Hamer D |title=A functional polymorphism in the monoamine oxidase A gene promoter |journal=Hum Genet |volume=103 |issue=3 |pages=273-9 |year=1998 |pmid=9799080}}</ref>
Recent [[Positron emission tomography|PET]] research has shown that MAO is also heavily depleted by [[tobacco]] use. Another interesting study reported in August 2002 concluded that "maltreated children with a genotype conferring high levels of MAO-A expression were less likely to develop antisocial problems" (Caspi 2002).
 
 
Recent research uncovered a possible link between predisposition to [[neophilia|novelty seeking]] and increased levels of MAO-A. [http://www.medialifemagazine.com/artman/publish/article_5439.asp]
 
   
 
==See also==
 
==See also==
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*[[Monoamine oxidase inhibitor]]
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*[[Genetics and violence]]
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*[[Neophilia]]
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*[[Warrior gene]]
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*[[Brunner syndrome]]
   
==References & Bibliography==
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==References==
  +
{{Reflist|2}}
 
==Key texts==
 
===Books===
 
===Papers===
 
 
==Additional material==
 
===Books===
 
===Papers===
 
* Caspi, A., Moffitt, T.E., & ''et al''. (2002). Role of genotype in the cycle of violence in maltreated children. ''Science'', 297:851-854. PMID 12161658
 
   
 
==External links==
 
==External links==
* [http://www.eurekalert.org/pub_releases/2001-11/euhs-sdt_1112101.php MAO-B Structure]
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* [http://www.eurekalert.org/pub_releases/2001-11/euhs-sdt_1112101.php MAO-B Structure at eurekalert.org]
* [http://alpha2.bmc.uu.se/gerard/research_mao.html Monoamine oxidase (MAO)]
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* [http://opm.phar.umich.edu/families.php?superfamily=128 Calculated orientations of Monoamine oxidases in membrane]
  +
* [http://alpha2.bmc.uu.se/gerard/research_mao.html Monoamine oxidase (MAO) at bmc.uu.se]
* [http://www.nida.nih.gov/meetsum/nicotine/slides/16Volkow/VolkowSlides.html Slides showing the effects of tobacco smoking on MAO]
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* [http://www.nida.nih.gov/meetsum/nicotine/slides/16Volkow/VolkowSlides.html Slides showing the effects of tobacco smoking on MAO at nida.nih.gov]
*[http://nepenthes.lycaeum.org/Misc/maoi.foods.html Foods to avoid when taking MAO inhibitors]
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*[http://nepenthes.lycaeum.org/Misc/maoi.foods.html Foods to avoid when taking MAO inhibitors at lycaeum.org]
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*[http://www.ihop-net.org/UniPub/iHOP/gs/89975.html Information Hyperlinked Over Proteins -- MAO-A]
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{{CH-NH2 oxidoreductases}}
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{{Mitochondrial enzymes}}
   
[[Category:Enzymes]]
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[[Category:Oxidases]]
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[[Category:Integral membrane proteins]]
   
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{{enWP|Monoamine oxidase}}
 
{{enWP|Monoamine oxidase}}

Revision as of 23:29, 30 March 2008

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MonoamineOxidase-1GOS

Monoamine Oxidase
monoamine oxidase A
Symbol(s): MAOA
Locus: X p11 .4-p11.3
EC number 1.4.3.4
EntrezGene 4128
OMIM 309850
RefSeq NM_000240
UniProt P21397
monoamine oxidase B
Symbol(s): MAOB
Locus: X p11 .4-p11.3
EC number 1.4.3.4
EntrezGene 4129
OMIM 309860
RefSeq NM_000898
UniProt P27338

Monoamine oxidases (singular abbreviation MAO) (EC 1.4.3.4) are enzymes that catalyze the oxidation of monoamines. They are found bound to the outer membrane of mitochondria in most cell types in the body. The enzyme was discovered by Mary Hare in the liver, and received the name of tyramine oxidase.[1] They belong to protein family of flavin containing amine oxidoreductases.

Locations of MAO-A and MAO-B

In humans there are two types of MAO: MAO-A and MAO-B.

Function

Monoamine oxidases catalyze the oxidative deamination of monoamines. Oxygen is used to remove an amine group from a molecule, resulting in the corresponding aldehyde and ammonia. The general form of the catalyzed reaction (with R denoting an arbitrary group) is

     H                      H
   R-C-NH2 + O2 + H2O  →  R-C=O + NH3 + H2O2 
     H

Monoamine oxidases contain the covalently-bound cofactor FAD and are thus classified as flavoproteins.

Subtype Specificities

MAO-A is particularly important in the catabolism of monoamines ingested in food. Both MAOs are also vital to the inactivation of monoaminergic neurotransmitters, for which they display different specificities.

Disorders resulting from MAO dysfunction

Because of the vital role that MAOs play in the inactivation of neurotransmitters, MAO dysfunction (too much/too little MAO activity) is thought to be responsible for a number of neurological disorders. For example, unusually high or low levels of MAOs in the body have been associated with depression, substance abuse, attention deficit disorder, and irregular sexual maturation. Monoamine oxidase inhibitors are one of the major classes of drug prescribed for the treatment of depression, although they are last line treatment due to risk of the drug's interaction with diet or other drugs. Excessive levels of catecholamines (epinephrine, norepinephrine, and dopamine) may lead to a hypertensive crisis, and excessive levels of serotonin may lead to serotonin syndrome.

PET research has shown that MAO is also heavily depleted by use of tobacco cigarettes.[2]

Genetics

The genes encoding MAO-A and MAO-B are located side-by-side on the short arm of the X chromosome, and have about 70% sequence similarity. Rare mutations in the gene are associated with Brunner syndrome.

A study reported in Science in August 2002 concluded that maltreated children with a low-activity polymorphism in the promoter region of the MAO-A gene were more likely to develop antisocial conduct disorders than maltreated children with the high-activity variant.[3] The suggested mechanism for this effect is the decreased ability of those with low MAO-A activity to quickly degrade norepinephrine, the synaptic neurotransmitter involved in sympathetic arousal and rage. This is alleged to provide direct support for the idea that genetic susceptibility to disease is not determined at birth, but varies with exposure to environmental influences.

Research also uncovered a possible link between predisposition to novelty seeking and a genotype of the MAO-A gene.[4]

In 2006, a New Zealand researcher, Dr Rod Lea said that a particular variant (or genotype) was over-represented in Māori, a Warrior gene. This supported earlier studies finding different proportions of variants in different ethnic groups. This is the case for many genetic variants, with 33% White/Non-Hispanic, 61% Asian/Pacific Islanders having the low-activity MAO-A promoter variant.[5]

See also

References

  1. Hare MLC (1928) Tyramine oxidase. I. A new enzyme system in liver. Biochem J 22:968Y979
  2. Fowler JS, Volkow ND, Wang GJ, Pappas N, Logan J, MacGregor R, Alexoff D, Wolf AP, Warner D, Cilento R, Zezulkova I (1998). Neuropharmacological actions of cigarette smoke: brain monoamine oxidase B (MAO B) inhibition.. Journal of addictive diseases.
  3. Caspi A, McClay J, Moffitt T, Mill J, Martin J, Craig I, Taylor A, Poulton R (2002). Role of genotype in the cycle of violence in maltreated children. Science 297 (5582): 851-4.
  4. The disorder of these times, neophilia, by Heidi Dawley, published June 18, 2006, retrieved on May 22, 2007
  5. Sabol S, Hu S, Hamer D (1998). A functional polymorphism in the monoamine oxidase A gene promoter. Hum Genet 103 (3): 273-9.

External links

Template:CH-NH2 oxidoreductases Template:Mitochondrial enzymes

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