Comparison of the structure of key variants of microcystin to vasopressin.

Microcystins (MCs) are cyclic heptapeptide compounds [where X(2) (position 2) and Z(4) (position 4) are variable l-aminoacids] produced by cyanobacteria and responsible for severe liver damage in animals ingesting acute doses of the toxic compounds. Certain variants of microcystins are more toxic than others, the differences being commonly ascribed to the hydrophobic nature of the variant. Microcystin-LR (MCLR) [X = l-leucine (L); Z = l-arginine (R); R1 = R2 = CH(3)] is the most toxic of all the microcystins investigated to date.