The van der Waals surface representation of the HPPK·HP·MgAMPCPP complex (Blaszczyk J, Shi G, Yan H, and Ji X. Structure 1999; 8:1049-58. Abstract) with blue and red colors indicate positive and negative electrostatic potentials, respectively. The AMPCPP molecule is illustrated as a stick model with atomic color scheme (carbon, white; nitrogen, blue; oxygen, red; and phosphorous, yellow).