Evolution of the haem-haem interaction in vertebrate haemoglobins - a hypothesis.

A hypothesis about the evolution of the haem-haem interaction in haemoglobins has been formulated on the basis of available functional and structural data. It emerges that this cooperative muchanism is not necessarily due solely to the higher levels of protomer aggregation, because it occurs only in haemoglobins having the distal histidine. It is thus proposed that this amino acid residue might have had a significant role for the development of low-oxygen-affinity haemoglobins in vertebrates.