Complete the sentences about heme. Some terms will not be used. The prosthetic group of hemoglobin and myoglobin is . The organic ring component of heme is . Under normal conditions, the central atom of heme is . In , the central iron atom is displaced 0.4 Å out of the plane of the porphyrin ring system. The central atom has bonds: to nitrogen atoms in the porphyrin, one to a residue, and one to oxygen. heme porphyrin Fe2+Fe2+ oxyhemoglobin six four cysteine