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^ Rashmi, Deo; Zanan, Rahul; John, Sheeba; Khandagale, Kiran; Nadaf, Altafhusain (2018). "γ-Aminobutyric Acid (GABA): Biosynthesis, Role, Commercial Production, and Applications". Studies in Natural Products Chemistry. Vol. 57. Elsevier. pp. 413–452. doi:10.1016/b978-0-444-64057-4.00013-2. ISBN978-0-444-64057-4. Alternate pathways of GABA synthesis from putrescine and other polyamines have also been reported . 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 . In response to abiotic stresses, GABA is also reported to be synthesized from proline via D1-pyrroline intermediate formation and also by a nonenzymatic reaction . However, GABA synthesis from polyamine pathways is minor in the brain, although they play a significant role in the developing brain and retina . But GABA can be formed from putrescine in the mammalian brain .
Shelp BJ, Bozzo GG, Trobacher CP, Zarei A, Deyman KL, Brikis CJ (September 2012). "Hypothesis/review: contribution of putrescine to 4-aminobutyrate (GABA) production in response to abiotic stress". Plant Sci. 193–194: 130–135. Bibcode:2012PlnSc.193..130S. doi:10.1016/j.plantsci.2012.06.001. PMID22794926.
Benedetti MS, Dostert P (1994). "Contribution of amine oxidases to the metabolism of xenobiotics". Drug Metab Rev. 26 (3): 507–535. doi:10.3109/03602539408998316. PMID7924902. 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 .