The porphine molecule forms an important part of the hemoglobin structure.Upon coordination to a metal the Hydrogen ions that are bonded to two of the four nitrogen atoms in porphine are displaced.Complexes derived from poprphine are called porphyrins and the iron pophyrin combination is called the heme group.The iron in the heme group has an oxidation number of +2 ; it iscoordinated to the four nitrogen atoms in the porphine group and also to a nitrogen donor atom in a ligand that is attached to the protein.