Haemoglobin

Oxygen is bound to the ferric ion (Fe2+) in the heme group in hemoglobin.
There are four heme groups in one hemoglobin (in each of the four domains of this protein). In other words, one hemoglobin molecule can bind up to 4 oxygen gas molecules.

You may have heard of a term "cooperativity",
which is actually one of the factors that affects the affinity.
Another factor can be pH.

It is correct that O2 has a higher affinity. If not, how can the nature employ it to carry O2 in our body? However, the affinity cannot be too high. Otherwise, it is not released to tissues which require oxygen ! The nature is miraculous, isn't it?

It is also correct that the affinity of CO is a lot higher than that of O2. This explains why CO can be fatal.

You may need to understand the protein quaternary structure or conformation of the protein "hemoglobin" and the prosthetic group and the neighbouring amino acid residues in order to understand how ligands (H2O, O2, and CO) bind and how strong they bind.

I suppose you can find more information on the internet.
Follow-up question is welcome. My email address is [email protected].

I guess:
Is it because of equilibrium?

4O2 + 4Hb <---> Hb4O8
increase O2 concentration during inhalation leads to equilibrium shift to right,
O2 are "forced" to form coordinate bonds with Hb

2012-04-29 12:34:14 補充：
while for N2
since it does not form complex with Hb
increase N2 concentration during inhalation have no effects??

Thank you so much for wasting time on my questions

I am told that although oxygen is weak toward reacting with Hb, the increase in partial pressure of it during inhalation increase the chance for it to bind with Hb. But i wonder why don't Hb carry nitrogen then -v-

Surely brings back memories.... I'll try to dig out my notes.

2012-04-30 01:59:32 補充：
That's not wasting time.
You've asked a meaningful question that many others wouldn't ever think about. Well done!

And I still haven't dug out the notes.
IIRC, it's sth abt the conjugation around Fe atom, which has sth deal with energy levels....