A so far unknown structural variant, called microginin FR1, of cyanobacterial peptides of the microginin type was isolated from a water bloom of a German lake. The bloom consisted almost exlusively of Microcystis sp. cells. The structure of microginin FR1 was identified by amino acid analysis, determination of the relative molecular mass by electrospray mass spectrometry, and by NMR to be a linear pentapeptide with a relative molecular mass of 727 which contains a β-amino-α-hydroxy-decanoic acid (Ahda), alanine, N-methyl-leucine, and two tyrosine units (Ahda-Ala-N-Me- Leu-Tyr-Tyr). Microginin FR1 had angiotensin-converting enzyme inhibitory activity with half-maximal inhibition at 6 x 10-5 M microginin FR1.
Neumann, U., Forchert, A., Flury, T., & Weckesser, J. (1997). Microginin FR1, a linear peptide from a water bloom of Microcystis species. FEMS Microbiology Letters, 153(2), 475–478. https://doi.org/10.1016/S0378-1097(97)00291-7