 Despite functional similarities with other heme enzymes, the structure of CPO is unique, which folds into a tertiary structure dominated by eight helical segments.The catalytic acid base, required to cleave the peroxide O-O bond, is glutamic acid rather than histidine as in horseradish peroxidase.As of late 2007, 30 structures have been solved for this class of enzymes, with PDB accession codes , , , , , , , , , , , , , , , , , , , , , , , , , , , , , and .