Okadaic acid is a toxin that accumulates in bivalves and causes diarrheal shellfish poisoning

Diarrheal shellfish poisoning

Diarrhetic shellfish poisoning is one of the four recognized symptom types of shellfish poisoning, the others being paralytic shellfish poisoning, neurotoxic shellfish poisoning and amnesic shellfish poisoning....

. The molecular formula of okadaic acid, which is a derivative of a C₃₈ fatty acid

Fatty acid

In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

, is C₄₄H₆₈O₁₃.

History

Okadaic acid was named from the marine sponge Halichondria okadai, from which okadaic acid was isolated for the first time. It has also been isolated from another marine sponge, H. malanodocia, as a cytotoxin. The real producers of okadaic acid belong to the algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

 group of the 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...

s, namely the benthic dinoflagellate Prorocentrum and the planktonic forms of
Dinophysis,
as for example Dinophysis acuminata.
Administration of okadaic acid has been shown to profoundly increase the secretion of nerve growth factor

Nerve growth factor

Nerve growth factor is a small secreted protein that is important for the growth, maintenance, and survival of certain target neurons . It also functions as a signaling molecule. It is perhaps the prototypical growth factor, in that it is one of the first to be described...

, and to also promote nerve growth factor gene transcription and the stability of mRNA in primary cultures of cortical astrocytes.

Biochemistry

The cytotoxicities of okadaic acid as EC₅₀

EC50

The term half maximal effective concentration refers to the concentration of a drug, antibody or toxicant which induces a response halfway between the baseline and maximum after some specified exposure time...

 against the P388 and L1210 cell lines are 1.7 nanomolar and 17 nanomolar, respectively. Additionally, okadaic acid strongly inhibits 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...

 serine

Serine

Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...

 / threonine

Threonine

Threonine is an α-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...

 phosphatase

Phosphatase

A phosphatase is an enzyme that removes a phosphate group from its substrate by hydrolysing phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl group . This action is directly opposite to that of phosphorylases and kinases, which attach phosphate groups to their...

 1, 2A, and 2B. The inhibitory effect of okadaic acid is strongest for 2A, followed by 1, and then 2B. The dissociation constant

Dissociation constant

In chemistry, biochemistry, and pharmacology, a dissociation constant is a specific type of equilibrium constant that measures the propensity of a larger object to separate reversibly into smaller components, as when a complex falls apart into its component molecules, or when a salt splits up into...

of the inhibition on protein serine / threonine phosphatase 2A is 30 picomolar.