[ADMAdda5]‐microcystins in Planktothrix agardhii strain PH‐123 (cyanobacteria)— importance for monitoring of microcystins in the environment

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Abstract
Two major and two minor microcystins (MCYST) were isolated from a hepatotoxic Danish strain of Planktothrix agardhii (Gomont) Anagnostidis et Komárek by reversed‐phase high‐performance liquid chromatography. The microcystins were characterized by UV spectroscopy, amino acid analysis, fast atom bombardment mass spectrometry (FABMS), and high‐resolution FABMS. The major microcystins were further analysed by collisionally induced tandem electrospray ionization MS. The microcystins were found to be demethylated variants of MCYST‐HtyR (homotyrosine‐arginine) and MCYST‐LR (leucine‐arginine). The two major microcystins contained an acetyl‐demethyl variant (ADMAdda) of 3‐amino‐9‐acetoxy‐2,6,8‐trimethyl‐10‐phenyldeca‐4,6‐dienoic acid (Adda). This is the first report of [ADMAdda5]‐microcystins in Planktothrix. The two [ADMAdda5]‐microcystins inhibited protein phosphatase activity but showed low cross‐reactivity with antibodies of an enzyme‐linked immunosorbent assay (ELISA), emphasizing the potential underestimation of the toxicity of natural blooms dominated by Planktothrix when microcystin content is quantified using only an ELISA. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 351–357, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10042