Medical Biochemistry

Structure of the Heme Prosthetic Group    Heme is the O2 – binding molecule common to Mb and Hb protophorphyrin IX is the backbone of heme when iron is complexed with protophorphyrin IX it is called Heme. So heme is the prosthetic group in Hemoglobin, Myoglobin and Cytochrome b, c, and c1. The Fe – porphyrin prosthetic group is, with the exception of two propionate groups, hydrophobic and planar. Heme become an integral part of the globin proteins during poly peptide synthesis. It is the heme molecule that give globin proteins their characteristic red brown colour. Once the Fe2+ (Ferrious) is incorporated, the protein is called hemoglobin. Such structural coordination creates an environment essential for Globin to bind and release O2. If the iron atom were to become oxidized to Fe3+(Ferric), the Globin would get changed to metmyoglobin or (Met hemoglobin) where heme can no longer interact with O2 and O2 transport is compromised. Fig 5.21: Structure of the heme prosthetic