Other Oxygen Binding Proteins and Metals in Biochemistry
There are other oxygen binding proteins in nature other than myoglobin and haemoglobin. Both of these proteins are found in vertebrates, however there are two other oxygen carriers which are normally found in invertebrates.
Hemocyanin is found in snails (mollusks) and crabs (arthropods). The oxygen binding site contains two Cu(I) ions attached directly to a protein. Interaction with oxygen causes the metal ions to become Cu(II).
Hemerythrin is found in a limited range of sea worms. The oxygen binding site in hemerythrin consists of two Fe(II) ions in close proximity: they are bound directly to donor atoms in the protein rather than to a heme macro cycle. The oxygen is bound in an end to end fashion as a hydro peroxide ion to one of the two iron atoms. Oddly, some of the organisms that use hemerythrin as an oxygen carrier employ the totally different protein myoglobin to store oxygen.
Other metal centers in biochemistry include, magnesium in chlorophyll
cobalt in coenzyme B12, and nickel in factor 430.