Aminopeptidases are a category of proteases that cleave peptides at the amino terminus, and are widely distributed in many organisms. Certain subtypes have found use within research and are commercially available. Methionine aminopeptidase can be used in removing N-terminal methionine residues from recombinant proteins. Aeromonas proteolytica aminopeptidase has been used in measuring the effectiveness of protease inhibitors, such as bestatin.