What exactly is this heme group?
A heme group consists of an iron atom (Fe) held in a heterocyclic ring, known as a porphyrin. This iron atom is the exact site of oxygen binding. An iron atom bonds with four nitrogens in the center of the ring and two additional bonds perpendicular to the plane on each side can be formed with the iron to form the fifth and sixth positions, one connected strongly to the protein, the other available for binding with oxygen.
