Question

How does CO change haemoglobin?

Answer 1

Same way O2 does. They're very similar molecules. Unfortunately, CO binds to the Fe in hemoglobin way more effectively than O2, so even a little CO in your air will displace all the O2 from your blood and suffocate you. Don't breathe CO.

Answer 2

Does it displace the O2 from only one haem group, four of them simultaneously?

Answer 3

Wikipedia seems to state that haemoglobin gains a higher affinity for oxygen in its remaining haem groups, thus cannot release the other O2. Is this incorrect?

Answer 4

I don't know the answer to either question. Try PubMed. They might have some scholarly articles on the exact mechanism of CO binding/debinding, and comparing it to O2. I do know the process is complicated, with not just the Fe/ligand electronic issues, but some crazy conformational fluctuations of the surrounding protein that matter very much. It's an area of active research.