English: Ribbon diagram of Cu,Zn superoxide dismutase subunit from the first crystal structure (PDB file 2sod). Cu,Zn SOD is a Greek key beta-barrel enzyme that protects against damage from the O-- radical. Active-site copper and zinc are labeled, and disulfide is a yellow zigzag. Hand drawn by Jane Richardson in 1981 and colored with cut-out film on the metals and colored pencils on the ribbons, to match the blue and blue-green colors given to the crystal by the copper site. Photographed and cleaned in 2002; touched up for pure white background in 2012.