annoyedWell, that might be true (and I'm not altogether convinced that it is) - but it's certainly not the main reason for it. The lecture notes and textbook I have in front of me both describe cooperativity of oxygen binding in terms of conformational changes as deoxyhaemoglobin changes to haemoglobin. Deoxyhaemoglobin is square pyramidal around the Fe(II) ion, whereas oxyhaemoglobin is octahedral around Fe(III). The change in oxidation state of the iron ion reduces its ionic radius and allows it to move upwards into the porphyrin ring. That then pulls the rest of the protein into a different conformation, which affects the remaining haemoglobin monomers.
But I can't do a damned thing about the article right now. Firstly, I don't want to be accused of plagiarism when I hand in coursework that's identical to the Wikipedia article! Secondly, I don't want to provide a perfect model answer for the rest of the lazy-ass students to copy & switch a few words around in. (I can talk about it here because no one from college reads my livejournal. Anyway, I haven't given the full answer.)
