This change places a hydrophobic residue on the surface on the protein. The conformational change that occurs following deoxygenation of hemoglobin generates a hydrophobic pocket on the b1-chain. So when HbS is deoxygenated, it polymerizes and forms very long fibers. These changes take place in people who have the sickle cell trait when they are exposed to low oxygen, such as at high altitude. At high oxygen the red blood is normal.
Porphyrias are diseases resulting from the abnormal accumulation of heme precursors.
In congenital erythropoietic porphyria, an excess of uroporphyrinogen I is present. In some individuals, hair growth is stimulated on the face. Medieval occurrences of this disorder may have given rise to legends of vampires and werewolves. In acute intermittent porphyria, porphobilinogen accumulates and leads to severe intermittent abdominal pain and mental dysfunction. It is thought that King George III of England had this disease during the American Revolution.