Three commercially available enzyme-linked immunosorbent assay (ELISA) kits and a non-commercial ELISA for the immunoassay of microcystins (cyanobacterial hepatotoxins) were tested with chemically produced conjugation products of microcystin-LR (MC-LR), a biologically derived MC-LR conjugate produced by a cytosolic extract of Artemia salina and authentic MC-LR. In all cases, the detoxified conjugation products were chromatographically distinguishable from the parent toxin in terms of retention time, but not in their UV absorption spectra, and were more immuno-reactive than MC-LR in the ELISAs. When initially dissolved in methanol, the highest cross-reactivity in the ELISAs was with the biologically derived glutathione MC-LR conjugate, followed by the chemically derived products in decreasing order of cross-reactivity: cysteine-glycine-MC-LR (cys-gly-MC-LR)>glutathione-MC-LR (GSH-MC-LR)>cysteine-MC-LR (cys-MC-LR). The authentic toxin (MC-LR) had the lowest cross-reactivity with all immunoassays. When the toxin conjugates were prepared and tested in water, the order of cross-reactivity was changed; the sequence was, in decreasing order: GSH-MC-LR>biologically derived glutathione conjugate>cys-MC-LR>cys-gly-MC-LR>MC-LR in all cases. No significant differences between cross-reactivity with microcystin products were found according to ELISA format or by the use of monoclonal versus polyclonal antibodies. The results are discussed in terms of the applicability of ELISAs for the detection and quantification of microcystins and their products in water bodies and organic matrices.

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