Heme oxygenase and iron: from bacteria to humans

Iron and iron-containing prosthetic groups are involved in many fundamental processes that constitute life. One of the biologically most important iron-containing groups is heme, in which an iron atom is co-ordinated to a protoporphyrin ring. Heme proteins have a wide range of functions, participating in a vast repertoire of biochemical reactions. Due to its abundance, heme also serves as an important source of iron. Enzymatic degradation of heme usually involves its oxidative cleavage by heme oxygenase. Not surprisingly, heme oxygenase activity is present in organisms across different domains and kingdoms. This review summarises the current knowledge in the dynamic relationship between heme oxygenase and iron in metabolism and in the clinical context.