These hemoglobin chains function to transport and deliver oxygen to tissues.
Ferric heme is incapable of binding oxygen because of a stoichiometric alteration of the molecule.
First, oxidizing agents are reduced by glutathione, which is maintained by the hexose-monophosphate shunt pathway of RBCs. This usually occurs before methemoglobinemia can be produced. Administration of methylene blue to such persons may induce hemolysis or methemoglobin formation. Oxidation of iron to the ferric state reduces the oxygen-carrying capacity of hemoglobin and produces a functional anemia. In addition, methemoglobinemia shifts the hemoglobin dissociation curve to the left.