Microcystins

Structural formula of microcystin LR.

As cyanotoxins, microcystins are toxins of certain cyanobacteria .

Chemical structure

Basic structure

Microcystins are cyclic heptapeptides or oligopeptides (referred to as cyanopeptides) with different amino acid sequences and thus belong to the proteins in the broader sense . To date, over 80 microcystin congeners are known. The atypical amino acid ADDA as a component is characteristic of microcystins . The mostly hydrophilic microcystins have different toxic effects.

Toxic Effects

The toxic effect is based on an inhibitory effect on the protein phosphatases PP1 and PP2A. Protein phosphatases are responsible for dephosphorylating other proteins. If this no longer happens, most of the proteins are in a phosphorylated state. This hyperphosphorylation leads to a breakdown of the cytoskeleton , the cells round off and perish. The ingestion of microcystins by cattle can lead to cattle death in polluted areas; in humans they can cause irritation of the mucous membranes and (sometimes allergic ) inflammatory reactions. After ingestion of larger quantities, diarrhea and vomiting can occur and a hepatotoxic ( liver toxic ) effect is evident . Orally ingested microcystins are absorbed in the small intestine . They finally reach the liver cells via the portal vein via special transporters ( OATPs ).

Occurrence

Microcystis aeruginosa

Microcystins are found in many species of cyanobacteria, most commonly in the genera Microcystis and Planktothrix . After the bacteria die, the toxins are released into the environment and can reach surface water and drinking water . Furthermore, microcystins can also be contained in finished products ( spirulina or AFA algae ) that are made from blue-green algae and are on the market as food supplements .

Limit values

In 1998 the World Health Organization (WHO) specified a preliminary guide value of 1 µg / l for one of the structural variants, microcystin-LR. This value is often used as an orientation for the other structural variants or the sum of all microcystins in a sample.

swell

ME van Apeldoorn: Toxins of cyanobacteria. In: Mol Nutr Food Res. Volume 51, 2007, pp. 7-60. PMID 17195276 , doi: 10.1002 / mnfr.200600185
BC Hitzfeld: Cyanobacterial toxins: removal during drinking water treatment, and human risk assessment. In: Environ Health Perspect . 108, Suppl 1, Mar 2000, pp. 113-122. PMID 10698727 , PMC 1637783 (free full text)

Individual evidence

↑ Toxic cyanobacteria in water: a guide to their public health consequences
↑ Wayne W. Carmichael, Val Beasley et al. a .: Naming of cyclic heptapeptide toxins of cyanobacteria (blue-green algae). In: Toxicon. 26, 1988, pp. 971-973, doi : 10.1016 / 0041-0101 (88) 90195-X .

[1] Toxic cyanobacteria in water: a guide to their public health consequences

[2] Wayne W. Carmichael, Val Beasley et al. a .: Naming of cyclic heptapeptide toxins of cyanobacteria (blue-green algae). In: Toxicon. 26, 1988, pp. 971-973, doi : 10.1016 / 0041-0101 (88) 90195-X .