Aminopeptidases selectively hydrolyze an aminoacid residue from the amino terminus of proteins and peptides resulting in their activation or inactivation. These enzymes are mainly metallo and belong, among other, to the M1 family of peptidases. One of its members, membrane glutamyl aminopeptidase (APA, EC 3.4.11.7) participates in many physiological processes, such as peptide metabolism related with blood pressure control, and last step of protein degradation. Furthermore, the up regulation of APA has been implicated in the pathogenesis of various human disorders like cancers, hypertension and glomerulosclerosis. APA is thus a target for the development of inhibitors with potential biomedical applications. We review the most important structural and functional characteristics of mammalian APA, focusing on the most recent data. Additionally, we integrate the roles of APA in physio- and pathophysio-logical processes of biomedical relevance with the development of specific APA inhibitors.

Bufadienolides are steroids that inhibit the Na+/K+ ATPase pump. Recent studies show that members of the bufadienolide family also inhibit the activity of aminopeptidase N (APN). APN is upregulated in different pathologies, including cancer and is a current target for drug development. Bufadienolides are cytotoxic in tumor cells, but there is no enough evidences that inhibition of APN activity contributes to their effect. In the present contribution we investigated the effect of another member of the bufadienolide family, bufotalin, on porcine APN (pAPN) activity. Bufotalin inhibited pAPN activity with K i values in the submicromolar range and an uncompetitive inhibition mechanism; it also inhibited porcine aminopeptidase A (pAPA) activity, but with a classical reversible competitive inhibition mechanism. In addition, we determined the effect of bufotalin on the viability/metabolism of APN+ A549, H292, MeWo and CT26 cancer cells. Bufotalin was cytotoxic in a dose dependent manner; the highest cytotoxicity was detected in A549 cells, the cells with the highest APN activity. Thus, tumor cell line sensitivity to the cytotoxic effect of bufotalin correlates with cell surface APN activity.