Heme

Consists of Iron in the center of a porphyrin Ring. Heme is a constituent of certain oxygen binding molecules such as hemoglobin or Myoglobin and in its normal state its iron is in the ferrous state (Fe++). When oxidized, the Fe++ (Hemoglobin) becomes Fe+++ (Methemoglobin). An example of this is noted in bleeding patients when their bright red blood (Fe++) is exposed to outside air and oxidized forming a dark brown color (Fe+++).