The interesting bit is the other position. The protein globin attaches to one of these positions using a lone pair on one of the nitrogens in one of its amino acids. The iron forms 4 co-ordinate bonds with the haem, but still has space to form two more - one above and one below the plane of the ring. We could simplify the heme with the trapped iron ion as:Įach of the lone pairs on the nitrogen can form a co-ordinate bond with the iron(II) ion - holding it at the center of the complicated ring of atoms. You aren't going to need to know the exact structure of the haem at this level.
They all have the same sort of ring system, but with different groups attached to the outside of the ring. Heme is one of a group of similar compounds called porphyrins. This is a sort of hollow ring of carbon and hydrogen atoms, at the center of which are 4 nitrogen atoms with lone pairs on them. The functional part of this is an iron(II) ion surrounded by a complicated molecule called heme. An example of this occurs in haemoglobin (American: hemoglobin). \) is chosen because it is very similar to the last one - except that it involves a transition metal.Ī quadridentate ligand has four lone pairs, all of which can bond to the central metal ion.
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