Fig. 3.

Electron density around the catalytic center. Catalytic residues E235 and E340 are shown as red balls and sticks and surrounding residues are in dark gray. Contours of the 2F_o–F_c map are shown as a blue mesh (at 1.2σ); contours of the F_o–F_c map are shown in green mesh (at 3σ) and in magenta (at −3σ). Several F_o–F_c peaks are visible in the active site, but they did not overlap with the 2F_o–F_c map, nor are they continuous; hence, at this resolution they appear to be noise. A and B show the catalytic centers of molecules A and B, respectively, in the asymmetric unit.