The calcium, copper and zinc content of some annelid extracellular haemoglobins.
The extracellular haemoglobins of Lumbricus and Tylorrhynchus contain 50 and 61 tightly bound calcium atoms per molecule, respectively. In addition, they contain one to four tightly bound copper and zinc atoms. Although the role of the latter is unknown, that of calcium is probably structural, assisting in the maintenance of the native hexagonal bilayer structure.