COLORIMETRIC PROTEIN PHOSPHATASE INHIBITION ASSAY OF LABORATORY STRAINS AND NATURAL BLOOMS OF CYANOBACTERIA - COMPARISONS WITH HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC ANALYSIS FOR MICROCYSTINS

Microcystins are cyclic heptapeptide hepatotoxins commonly produced by bloom-forming genera of cyanobacteria, These toxins are potent and sp ecific inhibitors of protein phosphatases 1 and 2A. We have optimised a rapid, simple and sensitive colorimetric protein phosphatase 1 inhib ition assay, utilising the activity of protein phosphatase 1 as expres sed in a recombinant strain of Escherichia coli, towards the chromogen ic substrate, p-nitrophenyl phosphate. A standard curve for the inhibi tion of protein phosphatase 1 by microcystin-LR was constructed with a n IC50 of about 38 ng ml(-1) and a limit of detection of 10-20 ng ml(- 1). Twenty-three laboratory-grown strains and 25 natural bloom samples of cyanobacteria were analysed by high-performance liquid chromatogra phy for microcystins and by the protein phosphatase 1 inhibition assay . Agreement for the microcystin contents of the samples detected by hi gh-performance liquid chromatography and the protein phosphatase 1 inh ibition assay showed good correlation (R-2 > 0.93, P < 0.0001). The su itability of the colorimetric protein phosphatase 1 inhibition assay a s a screen for cyanobacterial microcystins is discussed.