Due to eutrophication processes in our water bodies, cyanobacterial blooms can develop
worldwide. Most of these blooms are toxic. The most prominent cyanobacterial toxins are the group of
the microcystins, which are cyclic heptapeptides, currently with more than 100 congeners known. The
biotransformation of microcystins starts with the conjugation to the cell internal tripeptide glutathione,
catalysed by glutathione S-transferase enzymes. This conjugate is further broken down to a cysteine
conjugate, enhancing the cell internal transport and excretion of the conjugated toxin from the organisms. Still many
questions remain open, thinking on an obviously good working detoxification system on the one side and the often seen
negative effects up to the death of humans on the other sides.