The location of an enzyme’s active site is usually known prior to the determination of its three-dimensional structure. Analysis of sequence homology may indicate residues that are near an enzyme’s active site. Catalytic residues are often identified when site-directed mutagenesis experiments or chemical modification of residues lead to an alteration in enzyme activity. The enzyme’s three-dimensional (3D) structure is then used to supplement and interpret preceding experimental data. Occasionally, a new protein structure is solved before the active site has been located through conventional methods. Using the extracellular endonuclease fromSerratia marcescensas an example, we show here how the active site of an enzyme can sometimes be determined from electrostatic analysis of its 3D structure (1 ).
