The aryl group placement differs for pNPAc and mandelonitrile.

During ester hydrolysis (left scheme), the p-nitrophenyl moiety of the ester orients in the alcohol region of the substrate binding site. During cyanohydrin cleavage, the phenyl group of mandelonitrile orients in the acyl region of the substrate-binding site. The catalytic triad and oxyanion hole residues are in green, the residues associate with ester catalysis (Gly11, Met236) or HNL catalysis (Thr11, Lys236) are shown in red, the substrates are in black and the substrate binding site is shown schematically in magenta.