[ScuzzyTerminator]

The irreducibly complex part of the hemoglobin molecule would be the heme group (which I do not think is particularly complex, anyway). It is the functional part that binds to oxygen and is found in several globin forms, e.g. myoglobin.

This article is not very detailed, but if the protoglobins have a heme-like group of similar complexity, then this does not address ID.

[jennyp]

The irreducibly complex part of the hemoglobin molecule would be the heme group (which I do not think is particularly complex, anyway). It is the functional part that binds to oxygen and is found in several globin forms, e.g. myoglobin.

Is this what you're referring to?

Hemoglobin Cousins

Looking through the PDB, you will find many different hemoglobin molecules. You can find Max Perutz's groundbreaking structure of horse hemoglobin in entry 2dhb, shown in the picture here. There are structures of human hemoglobins, both adult and fetal. You can also find unusual hemoglobins like leghemoglobin, which is found in legumes. It is thought to protect the oxygen-sensitive bacteria that fix nitrogen in leguminous plant roots. In the past few years some hemoglobin cousins called the "truncated hemoglobins" have been identified, such as the hemoglobin in PDB entry 1idr, which have several portions of the classic structure edited out. The only feature that is absolutely conserved in this subfamily of proteins is the histidine amino acid that binds to the heme iron.