Editing Putrescine (section)

==Biochemistry==
[[File:Polyamine synthesis.svg|left|thumb|400x400px|Biosynthesis of spermidine and spermine from putrescine. Ado = 5'-adenosyl.]]
[[Spermidine synthase]] uses putrescine and [[S-Adenosylmethioninamine|''S''-adenosylmethioninamine]] (decarboxylated [[S-Adenosyl methionine|''S''-adenosyl methionine]]) to produce [[spermidine]]. Spermidine in turn is combined with another ''S''-adenosylmethioninamine and gets converted to [[spermine]].

Putrescine is synthesized in small quantities by healthy living cells by the action of [[ornithine decarboxylase]].

Putrescine is synthesized biologically via two different pathways, both starting from [[arginine]].

* In one pathway, arginine is converted into [[agmatine]]. The conversion is catalyzed by the enzyme [[arginine decarboxylase]] (ADC). Agmatine is transformed into N-carbamoylputrescine by [[Agmatine deiminase|agmatine imino hydroxylase]] (AIH). Finally, N-carbamoylputrescine  is hydrolyzed to give putrescine.<ref>{{cite journal|pmid=6895223|title=Enzymic conversion of agmatine to putrescine in Lathyrus sativus seedlings. Purification and properties of a multifunctional enzyme (putrescine synthase). | volume=256 | issue=18|date=September 1981|pages=9532–41|author=Srivenugopal KS, Adiga PR|journal=J. Biol. Chem.|doi=10.1016/S0021-9258(19)68795-8 |doi-access=free}}</ref>
* In the second pathway, arginine is converted into [[ornithine]] and then ornithine is converted into putrescine by [[ornithine decarboxylase]] (ODC).

Putrescine, via [[metabolic intermediate]]s including [[N-acetylputrescine|''N''-acetylputrescine]], [[gamma-Aminobutyraldehyde|γ-aminobutyraldehyde]] (GABAL), [[N-acetyl-γ-aminobutyric acid|''N''-acetyl-γ-aminobutyric acid]] (''N''-acetyl-GABAL), and [[N-acetyl-γ-aminobutyric acid|''N''-acetyl-γ-aminobutyric acid]] (''N''-acetyl-GABA), [[biotransformation]]s mediated by [[diamine oxidase]] (DAO), [[monoamine oxidase B]] (MAO-B), [[aminobutyraldehyde dehydrogenase]] (ABALDH), and other [[enzyme]]s, can act as a minor [[precursor (biochemistry)|biological precursor]] of [[γ-aminobutyric acid]] (GABA) in the [[brain]] and elsewhere.<ref name="RashmiZananJohn2018">{{cite book | last1=Rashmi | first1=Deo | last2=Zanan | first2=Rahul | last3=John | first3=Sheeba | last4=Khandagale | first4=Kiran | last5=Nadaf | first5=Altafhusain | title=Studies in Natural Products Chemistry | chapter=γ-Aminobutyric Acid (GABA): Biosynthesis, Role, Commercial Production, and Applications | publisher=Elsevier | volume=57 | date=2018 | isbn=978-0-444-64057-4 | doi=10.1016/b978-0-444-64057-4.00013-2 | pages=413–452 | url=https://www.researchgate.net/publication/324580560 | quote=Alternate pathways of GABA synthesis from putrescine and other polyamines have also been reported [207–211]. Here, γ-aminobutyraldehyde, an intermediate from polyamine degradation reaction via combined activities of diamine oxidase (DAO, E.C. 1.4.3.6) and 4-aminobutyraldehyde dehydrogenase (ABALDH), leads to the synthesis of GABA [205,212,213]. In response to abiotic stresses, GABA is also reported to be synthesized from proline via D1-pyrroline intermediate formation [47,205,214] and also by a nonenzymatic reaction [214]. However, GABA synthesis from polyamine pathways is minor in the brain, [215] although they play a significant role in the developing brain [216] and retina [217]. But GABA can be formed from putrescine in the mammalian brain [218].}}</ref><ref name="ShelpBozzoTrobacher2012">{{cite journal | vauthors = Shelp BJ, Bozzo GG, Trobacher CP, Zarei A, Deyman KL, Brikis CJ | title = Hypothesis/review: contribution of putrescine to 4-aminobutyrate (GABA) production in response to abiotic stress | journal = Plant Sci | volume = 193-194 | issue = | pages = 130–135 | date = September 2012 | pmid = 22794926 | doi = 10.1016/j.plantsci.2012.06.001 | bibcode = 2012PlnSc.193..130S | url = }}</ref><ref name="BenedettiDostert1994">{{cite journal | vauthors = Benedetti MS, Dostert P | title = Contribution of amine oxidases to the metabolism of xenobiotics | journal = Drug Metab Rev | volume = 26 | issue = 3 | pages = 507–535 | date = 1994 | pmid = 7924902 | doi = 10.3109/03602539408998316 | url = | quote = MAO also catalyses the deamination of a natural brain constituent, monoacetyl-putrescine, producing y-acetylaminobutyraldehyde, which in turn participates in the formation of brain GABA [13].}}</ref><ref name="WatanabeMaemuraKanbara2002">{{cite book | vauthors = Watanabe M, Maemura K, Kanbara K, Tamayama T, Hayasaki H | title = A Survey of Cell Biology | chapter = GABA and GABA Receptors in the Central Nervous System and Other Organs | series = International Review of Cytology | volume = 213 | pages = 1–47 | date = 2002 | pmid = 11837891 | doi = 10.1016/s0074-7696(02)13011-7 | isbn = 978-0-12-364617-0 | url = }}</ref><ref name="Seiler2004">{{cite journal | vauthors = Seiler N | title = Catabolism of polyamines | journal = Amino Acids | volume = 26 | issue = 3 | pages = 217–233 | date = June 2004 | pmid = 15221502| doi = 10.1007/s00726-004-0070-z | url = }}</ref><ref name="ChoKimSim2021">{{cite journal | vauthors = Cho HU, Kim S, Sim J, Yang S, An H, Nam MH, Jang DP, Lee CJ | title = Redefining differential roles of MAO-A in dopamine degradation and MAO-B in tonic GABA synthesis | journal = Exp Mol Med | volume = 53 | issue = 7 | pages = 1148–1158 | date = July 2021 | pmid = 34244591 | pmc = 8333267 | doi = 10.1038/s12276-021-00646-3 | url = }}</ref> In 2021, it was discovered that MAO-B does not mediate [[dopamine]] [[catabolism]] in the rodent [[striatum]] but instead participates in striatal GABA synthesis and that synthesized GABA in turn inhibits [[dopaminergic]] [[neuron]]s in this brain area.<ref name="NamSaJu2022">{{cite journal | vauthors = Nam MH, Sa M, Ju YH, Park MG, Lee CJ | title = Revisiting the Role of Astrocytic MAOB in Parkinson's Disease | journal = Int J Mol Sci | volume = 23 | issue = 8 | date = April 2022 | page = 4453 | pmid = 35457272 | pmc = 9028367 | doi = 10.3390/ijms23084453 | doi-access = free | url = }}</ref><ref name="ChoKimSim2021" /> It has been found that MAO-B, via the putrescine pathway, importantly mediates GABA synthesis in [[astrocyte]]s in various brain areas, including in the [[hippocampus]], [[cerebellum]], striatum, [[cerebral cortex]], and [[substantia nigra pars compacta]] (SNpc).<ref name="NamSaJu2022" /><ref name="ChoKimSim2021" />