Figure 2.

(a) Simulated annealing omit map showing trifluoromethylketone 1 bound as a gem-diol in the active site of APAH (monomer B, contoured at 3.5σ). Atomic color codes are as follows: C = wheat (protein, monomer B), brown (monomer A), or green (inhibitor), N = blue, O = red, F = light cyan, Zn²⁺ = magenta sphere. Water molecules are represented as red spheres. Metal coordination and selected hydrogen bond interactions are shown as solid black or dashed black lines, respectively. (b) Stereoview of the N⁸-acetylspermidine substrate bound in the active site of the inactive mutant APAH H159A (PDB accession code 3Q9C, monomer A). Atomic color codes are identical to those in (a); C atoms in brown correspond to adjacent monomer I of the APAH dimer. We note that in monomer J only of this structure, the secondary amine of N⁸-acetylspermidine donates a hydrogen bond to E117. Additionally, a water molecule makes a bridging interaction in some monomers between Y19 and the terminal amino group of the substrate. (c) Simulated annealing omit map of thiol 2 bound in the active site of APAH (monomer A, contoured at 3.0σ). Atomic color codes are identical as in (a), with S = gold.