49 PRODUCTION OF NEW PEPTIDES BY TOXIC CYANOBACTERIA AND ITS ECOLOGICAL ASPECTS

Microcystins, cyclic heptapeptides, are produced by cyanobacteria and show severe hepatotoxicity. It is also demonstrated that microcystins inhibit protein phosphatases 1 and 2A as strongly as "okadaic acid class" compounds and are a tumor promoter of liver. However, recent advance of researches on biological activity by microcystins suggests that other types of compounds than microcystins, which are simultaneously produced by cyanobacteria, are deeply concerned with the characteristic biological activities caused by toxic cyanobacteria. Four novel depsipeptides, aeruginopeptins (1-4) were isolated from toxic cyanobacteria, Microcystis aeruginosa TAC 95 and M228 which also produce large amounts of microcystins LR and YR, respectively. Their structures were mainly determined by 2D NMR techniques and MS/MS method. In a screening of structurally related peptides to aeruginopeptins it was found that such three peptides were produced by bloom cells collected in Lake Suwa on July 23, 1991. They were tentatively named as 917S and their structures were determined as 5-7 by MS/MS. Although biological activity of the present peptides has not been investigated in detail, a simultaneous administration of 1 with microcystin LR enhanced the toxicity compared with that of microcystin LR alone. In the present study the relationship between species of Microcystis and production of microcystins and aeruginopeptins in bloom cells, which were regularly collected in Lake Suwa in every ten days in summer season of 1991, was extensively investigated. The accumulated data strongly suggest that M. aeruginosa (Large) produces mainly both compounds and the production of aeruginopeptins was closely related to that of microcystins.