Heme is a prosthetic group best known for roles in oxygen transport, oxidative catalysis, and
respiratory electron transport. Recent years have seen the roles of heme extended to
sensors of gases such as O 2 and NO and cell redox state, and as mediators of cellular
responses to changes in intracellular levels of these gases. The importance of heme is
further evident from identification of proteins that bind heme reversibly, using it as a signal,
eg to regulate gene expression in circadian rhythm pathways and control heme synthesis …