The metal center in both hemoglobin and myoglobin is an iron Fe atom, which is coordinated within a heme group. The coordination geometry of the iron atom in these metalloproteins is octahedral, and the coordination number is 6.In the heme group, four of the six coordination sites are occupied by nitrogen atoms from a porphyrin ring. The fifth coordination site is occupied by a nitrogen atom from a histidine residue in the protein. This histidine residue is part of the protein structure and helps to anchor the heme group within the protein.The sixth coordination site is where oxygen O2 binds. In the absence of oxygen, this site is vacant or sometimes occupied by a water molecule. When oxygen is present, it binds to the iron atom, forming a bond with the metal center. This binding of oxygen to the iron atom causes a slight change in the geometry of the iron atom, which in turn leads to conformational changes in the protein structure.In hemoglobin, these conformational changes facilitate cooperative binding of oxygen, meaning that the binding of one oxygen molecule to a subunit of hemoglobin increases the affinity of the other subunits for oxygen. This cooperative binding allows hemoglobin to efficiently pick up oxygen in the oxygen-rich environment of the lungs and release it in the oxygen-poor environment of the tissues.Myoglobin, on the other hand, does not exhibit cooperative binding. It has a higher affinity for oxygen than hemoglobin, allowing it to effectively store and release oxygen in muscle tissues. Myoglobin serves as an oxygen reservoir and facilitates oxygen diffusion within the muscle cells.In summary, the octahedral coordination geometry and coordination number of 6 in the metal center of hemoglobin and myoglobin play a crucial role in the binding and transport of oxygen in these metalloproteins. The specific interactions between the iron atom and oxygen, as well as the protein conformational changes, enable efficient oxygen transport and storage in the body.