The schematic representation of the HPPK·HP·MgAMPCPP complex (Blaszczyk, Shi, Yan, and Ji. Structure 1999; 8:1049-58. Abstract) is shown in (a). Panels (b) and (c) show the final electron density for enzyme-bound HP and MgAMPCPP contoured at 1.0 and 2.5 sigma, respectively.