Maitotoxin is an extremely potent toxin

Toxin

A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

 produced by Gambierdiscus toxicus, a dinoflagellate

Dinoflagellate

The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...

 species. Maitotoxin is so potent that it has been demonstrated that an intraperitoneal

Peritoneum

The peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...

 injection of 0.13 µg

Microgram

In the metric system, a microgram is a unit of mass equal to one millionth of a gram , or 1/1000 of a milligram. It is one of the smallest units of mass commonly used...

/kg was lethal in mice. Maitotoxin was named from the ciguateric

Ciguatera

Ciguatera is a foodborne illness caused by eating certain reef fishes whose flesh is contaminated with toxins originally produced by dinoflagellates such as Gambierdiscus toxicus which lives in tropical and subtropical waters. These dinoflagellates adhere to coral, algae and seaweed, where they are...

 fish Ctenochaetus striatus

Ctenochaetus striatus

Ctenochaetus striatus is a Tang from the Indo-Pacific. It occasionally makes its way into the aquarium trade. It grows to a size of 26 cm in length....

—called "maito" in Tahiti

Tahiti

Tahiti is the largest island in the Windward group of French Polynesia, located in the archipelago of the Society Islands in the southern Pacific Ocean. It is the economic, cultural and political centre of French Polynesia. The island was formed from volcanic activity and is high and mountainous...

—from which maitotoxin was isolated for the first time. It was later shown that maitotoxin is actually produced by Gambierdiscus toxicus.

Mechanism of toxicity

Maitotoxin activates Ca²⁺ permeable, non-selective cation channels, leading to an increase in levels of cytosolic Ca²⁺ ions. It is thought that maitotoxin leads to the formation of pores on these ion channels. Ultimately, a cell death cascade is activated, resulting in membrane blebbing and eventually cell lysis. Maitotoxin is known to activate cytosolic calcium-activated proteases calpain-1 and calpain-2, contributing to necrosis. The toxicity

Toxicity

Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...

 of maitotoxin to mice is the highest for nonprotein toxins: the LD50 is 50 ng/kg.

Molecular Structure

The molecule

Molecule

A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

 itself is a system of 32 fused rings. It is notable because it is one of the largest and most complex non-protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

, non-polysaccharide

Polysaccharide

Polysaccharides are long carbohydrate molecules, of repeated monomer units joined together by glycosidic bonds. They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure,...

 molecules produced by an organism

Organism

In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

. Maitotoxin includes 32 ether

Ether

Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...

 rings, 22 methyls, 28 hydroxyls, and 2 sulfuric acid

Sulfuric acid

Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

 esters and has an amphipathic structure. Its structure was established through analysis using nuclear magnetic resonance

Nuclear magnetic resonance

Nuclear magnetic resonance is a physical phenomenon in which magnetic nuclei in a magnetic field absorb and re-emit electromagnetic radiation...

 at Tohoku University, Harvard and the University of Tokyo

University of Tokyo

, abbreviated as , is a major research university located in Tokyo, Japan. The University has 10 faculties with a total of around 30,000 students, 2,100 of whom are foreign. Its five campuses are in Hongō, Komaba, Kashiwa, Shirokane and Nakano. It is considered to be the most prestigious university...

 in combination with mass spectrometry

Mass spectrometry

Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...

, and synthetic chemical methods. However, Gallimore and Spencer recently questioned the structure of maitotoxin at a single ring-junction (the J-K junction), based purely on biosynthetic considerations and their general model for marine polyether biogenesis.
Nicolaou and Frederick on the other hand argue that despite this biosynthetic argument, the originally proposed structure could still be correct.

The controversy has yet to be resolved.