The van der Waals surface representation of the HPPK·HP·MgADP complex (Xiao B, Shi G, Gao J, Blaszczyk J, Liu Q, Ji X, and Yan H. J. Biol. Chem. 2001; 276:40274-40281. Abstract) with blue and red colors indicate positive and negative electrostatic potentials, respectively. The ADP molecule is illustrated as a stick model with atomic color scheme (carbon, white; nitrogen, blue; oxygen, red; and phosphorous, yellow).