Comparison of hydrogen bonding and subsites residues. Main chain hydrogen bonding interactions of the inhibitor phosphoramidon with (A) XCE and (B) ECE-1. (C) Amino acid residues of the S1’ pocket of XCE and (D) ECE-1. (E) Amino acid residues of the S2’ pocket of XCE and (F) ECE-1. Hydrophobic surfaces are shown in yellow, positively changed areas in blue and negatively charged surfaces in red.Ligand phosphoamidon is shown in ball and stick model whreas amino acids of the pocket are depicted in sticks.