The characterization of two aminopeptidase activities from the cyanobacterium Anabaena flos-aquae

Aminopeptidase activity, indicated by hydrolysis of the synthetic substrate alanine p-nitroanilide, was identified in the cyanobacterium Anabaena flos-aquae. On purification, 2 enzymes were separated by gel filtration chromatography, a 188 kDa multimer (AP-I) and a 59 kDa monomeric metalloprotein (AP-II). Their activities against a range of alanine-containing peptides were screened. Both enzymes were capable of removing a variety of N-terminal residues, including proline. Neither removed N-terminal acidic residues. The activity of AP-I appeared to be limited to di- and tri-peptides, while AP-II was capable of hydrolysing (Ala)5. It was not possible to assign the active-site chemistry of AP-I to one of the known hydrolase subgroups as none of the potential inhibitors tested had a significant inhibitory effect. This is the first reported purification of aminopeptidases from a cyanobacterium.