The two aminoacids at the botton (the distal histidine and the distal valine) touch the heme but are not bounded to it. The proximal histidine is the principal path for comunicatión between the heme and the rest of the molecule. It forms a chemical bond with the heme iron. In oxy state hemoglobin the iron is aligned in the center of hemo group. In the deoxy form the iron is displaced 0.5 amstrong off the heme center approaching to the proximal histidine, which is moved in the same direction, offseting it. Which leads a conformational change which is transmited over the entire molecule.