Figure 3. Active site of PTDH in complex with the competitive inhibitor sulfite.

A. The inhibitor is colored in orange, the cofactor is shown in green ball-and-stick and active site residues are colored in yellow. Superimposed is a difference Fourier electron density map contoured at 3σ over background (in blue) and 8σ over background (in yellow), calculated with coefficients |F_obs | - |F_calc | and phases from the final refined model with the coordinates of sulfite deleted prior to one round of refinement. B. A superposition of the active sites of unliganded PTDH (in cyan) with the sulfite complex (in yellow). Note the movement of Met-53 that results in the formation of a defined substrate-binding pocket.