Cartoon representation of hen eggwhite lysozyme, the first enzyme structure solved: http://en.wikipedia.org/wiki/Lysozyme The catalytic residues are represented as spheres. The model was created using Protein Data Bank entry 2LYZ: http://www.rcsb.org/pdb/explore.do?structureId=2lyz The model was created with VMD: http://www.ks.uiuc.edu/Research/vmd/