FATTY-ACIDS FROM THE CYANOBACTERIUM MICROCYSTIS-AERUGINOSA WITH POTENT INHIBITORY EFFECTS ON FISH GILL NA+ K+-ATPASE ACTIVITY/

Fatty acids from two strains of the cyanobacterium Microcystis aerugin osa, PCC 7820 (a strain that produces the hepatotoxin microcystin-LR, MC-LR) and CYA 43 (a strain that produces only small quantities of MC- LR), were extracted, partially characterised and tested for their inhi bitory effect on the K+-dependent p-nitrophenol phosphatase (pNPPase) activity of tilapia (Oreochromis mossambicus) gill basolateral membran e, Thin-layer chromatography of the lipids from dichloromethane:methan ol extracts of M. aeruginosa PCC 7820 and CYA 43, using diethylether:i sopropanol:formic acid (100:4.5:2.5) as solvent, yielded five inhibito ry products from M. aeruginosa 7820 and six from M. aeruginosa CYA 43. None of these products could be related to MC-LR. The inhibitory beha viour of the products mimics that of a slow, tight-binding inhibitor, The inhibitory activity is removed by incubation of extracts with fatt y-acid-free bovine serum albumin (FAF-BSA). However, FAF-BSA only part ially reversed the inhibition of K+-dependent pNPPase on fish gills pr e-exposed to the extracted products, We conclude that M. aeruginosa st rains PCC 7820 and CYA 43 produce fatty acids with potent inhibitory e ffects on K+-dependent pNPPase, The release of these products followin g lysis of cyanobacterial blooms may help to explain fish kills throug h a disturbance of gill functioning.