Monoamine Oxidase

Also found in: Dictionary, Thesaurus, Medical, Financial, Wikipedia.

Monoamine oxidase

Either of two enzymes found in the outer membrane of mitochondria that degrade biogenic amines and are thus responsible for the destruction of transmitter substances at neuronal synapses. Nerve cells release neurotransmitter into the synapse in response to stimulation. The neuron must then dispose of this neurotransmitter to stop the signal or a new signal cannot get through. This is accomplished by one of three mechanisms: diffusion; reuptake into the presynaptic area; and degradation by a number of enzymes, including monoamine oxidase. See Synaptic transmission

Monoamine oxidase inhibitors are drugs that block degradation of amine transmitters within the cell; however, not all of their effects can be attributed directly to monoamine oxidase inhibition, since a number of different neuronal effects have been described. The most prominent consequence of monoamine oxidase inhibition is a rapid increase in the intracellular concentrations of monoamines. In addition, the level of serotonin in the brain is raised to a greater extent than that of norepinephrine and dopamine. After these amine concentrations rise, secondary adaptive consequences occur, including a reduction in amine synthesis via an apparent feedback mechanism, which has been most clearly demonstrated for the noradrenergic system. See Neurobiology, Serotonin

Two types of monoamine oxidase have been identified. These are designated A and B and are distinguished by having different substrate specificity. Type A preferentially deaminates norepinephrine, cortical dopamine, and serotonin, and is selectively inhibited by clorgyline. Type B degrades phenylethylamine, dopamine, and benzylamine, and is sensitive to deprenyl or pargyline inhibition. Commonly used monoamine oxidase inhibitors are nonselective inhibitors that affect types A and B. Seventy-five percent of monoamine oxidase in the human is type B.

Monoamine oxidase inhibitors are used in medicine for controlling hypertension and for treating depression and other disorders. Other psychiatric disorders, such as obsessive-compulsive disorder, bulimia, somatoform pain disorder, panic disorder, and schizophrenia, have been reported to occasionally respond to treatment with monoamine oxidase inhibitors. There is also some evidence that patients with so-called atypical depression preferentially respond to monoamine oxidase inhibitors. See Affective disorders

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Monoamine Oxidase


an enzyme of the oxidoreductase class that catalyzes the oxidative deamination of monoamines, including biogenic amines. Monoamine oxidase is present in the outer membrane of mitochondria, with which it forms strong lipoprotein complexes. Flavin adenine dinucleotide (FAD), covalently bonded to protein, is a coenzyme (prosthetic group) of monoamine oxidase.

The presence of sulfhydryl (—SH) groups that are not, however, part of the active center of the enzyme is important for the activity of monoamine oxidase. Differences in the properties of enzyme systems of amino deamination (substrate specificity, reactivity to inhibitors such as 8-oxyquinoline, hydrazine derivatives, and certain alkaloids), observed in different species of animals and in different kinds of tissue, led to the concept of monoamine oxidase multiplicity. However, all attempts to isolate specific types of monoamine oxidase were unsuccessful. Monoamine oxidase apparently takes part not only the decomposition but also in the formation of biologically active compounds.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

monoamine oxidase

[män·ō′am‚ēn ′äk·sə‚dās]
A mitochondrial enzyme which oxidatively deaminates intraneuronal biogenic amines, some of which are important neurotransmitters in the peripheral and central nervous system.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
In the past decade, monoamine oxidases (MAOs) with 2 isoforms (A and B) at the outer mitochondrial membrane have emerged as sources for constant [H.sub.2][O.sub.2] generation in heart and vessels (for a recent comprehensive review see [17]).
Furthermore, monoamine oxidase B inhibition has been observed for rutin and quercetin with [IC.sub.50] of 3.89 and 10.89 [mu]M, respectively (Lee et al.
Brain neurotransmitters play a key role in female sexual dysfunction, notably the compound monoamine oxidase (MAO).
Treatment of tricyclic refractory depression with a monoamine oxidase inhibitor antidepressant.
Giorgio, "Mitochondrial pathways for ROS formation and myocardial injury: the relevance of p66Shc and monoamine oxidase," Basic Research in Cardiology, vol.
Monoamine oxidase is an enzyme found in both neurons and liver cells.
Among their topics are contributions to aggressive behavior from genes on the Y chromosome, quantitative trait locus analysis of aggressive behaviors in mice, the molecular architecture of pheromone sensing in mammals, serotenergic mechanisms in aggression, a typology of human aggression and its biological control, and the important of gene-environment interactions in the role of monoamine oxidase A in the etiology of antisocial behavior.
To prevent a potentially fatal reaction, do not use an antidepressant if you have taken a monoamine oxidase inhibitor within the last 14 days.
5-Hydroxyindoloeacteic HVA acid Disorders of BH4 [down arrow] [down arrow] synthesis (recessive) GTP cyclohydrolase (dominant) [down arrow] N Tyrosine hydroxylase [down arrow] N Tryptophan hydroxylase (a) N [down arrow] AADC [down arrow] [down arrow] PNPO (b) [down arrow] [down arrow] Dopamine [beta]-hydroxylase [up arrow] N Monoamine oxidase [down arrow] [down arrow] MHPG 3-O-methyldopa Disorders of BH4 [down arrow] N synthesis (recessive) GTP cyclohydrolase (dominant) N N Tyrosine hydroxylase [down arrow] N Tryptophan hydroxylase (a) N N AADC [down arrow] [up arrow] PNPO (b) [down arrow] [up arrow] Dopamine [beta]-hydroxylase [down arrow] N Monoamine oxidase [down arrow] N N, normal; [down arrow], decreased; [up arrow], elevated.
It is also believed to be a weak inhibitor of monoamine oxidase activity.
The data from these two Phase III trials demonstrated that opicapone improved motor fluctuations in levodopa-treated patients regardless of concomitant dopamine agonist or monoamine oxidase type B inhibitors used.