Substrate specificity of NmAPN for ACC non-natural amino acids. Substrates bearing a linear, non-substituted side chain are colored blue, hydrophobic, branched aliphatic and cycloaliphatic – red, heteroatom-containing aliphatic and cycloaliphatic – green, aromatic and heteroaromatic – orange. Y-axis represents the rate of hydrolysis, proportional to the kcat/Km value, expressed as the percentage of the best substrate cleavage (L-hArg-ACC, 100%). Error bars represent standard deviation. ACC derived pyrrolidin-2-yl-L-Ala, 2S,3S-Apns, L-Dab, L-Tic, β-Ala, 6-Ahx, L-Phg, 4-I-L-Phe, 4(1-carboxymethoxy)-L-Phe, L-Dab(Z), 4-guanidino-L-Phe, L-Tyr(Bzl), L-Cit, L-Tle, L-Chg, L-Agp were not hydrolyzed.