Figure 1.

The highly toxic microcystin-LR variant. The microcystin chemical structure can be generalized as cyclo-D-Ala¹-X²-D-MeAsp³-Z⁴-Adda⁵-D-Glu⁶-Mdha⁷ where X and Z denote the highly variable second and fourth positions. Microcystins may contain L-Ala, L-Arg, L-Glu, L-Hil, L-Hph, L-Hty, L-Leu, L-Met, L-Phe, L-Try, L-Tyr, or L-Val at the X position and L-Aba, L-Ala, L-Arg, L-Glu, L-Har, L-Leu, L-Met, L-Phe, L-Try, or L-Tyr at the Z position [1].