Occurrence of protease inhibitors in freshwater cyanobacterium Woronichinia naegeliana (Unger) Elenkin.

Cyanobacteria are known for producing a wide array of secondary metabolites, including non-ribosomally synthesized oligopeptides, whose functions remain to be determined. Woronichinia naegeliana, a common component of freshwater blooms, represents an under-explored resource of bioactive oligopeptides. Among these oligopeptides are cyanopeptolin 1081 and anabaenopeptin 899, which have been shown to have adverse effects on zooplankton. The absolute amino acid configuration of these peptides appears typical relative to other cyanopeptolins and anabaenopeptins. To understand their toxic mechanisms, enzyme assays were conducted. The inhibitory activity of cyanopeptolin 1081 and anabaenopeptin 899 was tested against proteases such as chymotrypsin, trypsin, elastase, thrombin, and carboxypeptidase A, resulting in different activities against these enzymes. Cyanopeptolin 1081 inhibited both chymotrypsin and elastase, while anabaenopeptin 899 inhibited carboxypeptidase A but failed to inhibit the other tested enzymes at a concentration of 37 μM. The inhibitory concentration values determined here highlight that these compounds are among the most potent enzyme inhibitors in freshwater-derived cyanopeptides.