Anatoxin-A - a neurotoxic amine
Anatoxin A (ATX-A) is a semi-rigid bicyclic secondary amine molecule that presents acute neurotoxic activity. It is naturally produced by at least five genus of freshwater cyanobacteria
Molecular weight: 166.24 g/mol
IUPAC name: 1-(9-azabicyclo(4.2.1)non-2-en-2-yl)-ethanone
Anatoxin A (ATX-A) is a semi-rigid bicyclic secondary amine molecule that presents acute neurotoxic activity. The enantiomer (+)-anatoxin-a is naturally produced by at least five genus of freshwater cyanobacteria, including several strains of Anabaena (i.e. Anabaena circinalis, Anabaena flos-aquae NRC 44-1 and Anabaena flos-aquae NRC 525-17), Aphanizomenon, Microcystis, Planktothrix and Oscillatoria.
As a toxin, ATX-A is a nicotinic agonist that binds irreversibly to nicotinic acetylcholine receptors (nAChRs) in neurons and neuromuscular junctions. Its interaction with nAChRs causes the opening of the Na+/Ca2+ channels and, ultimately, causes its blockage, resulting in muscular malfunction. In acute toxicity tests, the administration of (+)-anatoxin-a has been observed to cause loss of coordination (altered gait and tremors), hyperactivity, muscular twitching and death by respiratory paralysis (LD=13.3 mg kg-1 in male Swiss Webster ND-4 mice).
Cases of human injury through cyanotoxins are well documented. The most common route of exposure is drinking water, causing - in some cases serious - illness through ingestion or aspiration of toxic cyanobacteria.
In the aquatic system, ATX-A is expected to largely remain in solution (solubility 7.2·104 mg/l), without being significantly adsorbed to particulate material or sediment (estimated KOC=76). Its bioaccumulation potential is also suggested to be low (BCF=2.6, estimated from a log KOW of 1.1). ATX degrades in water, particularly at high pH waters (ATX-A was found to be stable for 21 days at pH 4, but less than 5 % remained at pH 8-10 after 2 weeks) and in presence of sunlight irradiation. The degradation of ATX-A produces several non-toxic compounds, including the hydrogenated form, dihydroanatoxin-A, and anatoxin-A epoxide, both of which have been detected in the real environment. Volatilization from water surfaces is not favoured, based upon an estimated Henry's Law constant of 6.6·10-9 atm m3 mol-1 (SRC). In air, ATX-A remains in the vapour phase and is readily degraded by hydroxyl radicals (half-life, 1.1 h)
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- Anabaena circinalis By Bdcarl - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=19074360.
- Oscillatoria. Photo: Otago Regional Council & Landcare Research.
- Planktothrix rubescens. By Kristian Peters http://www.korseby.net/outer/flora/algae/index.html - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9432593
Dr Marinelle Farré