Variation in the Structure of Haemoglobin?

[Theophrastus]

Greetings to all,

I've been reading up on some biochemistry recently, and one example in the text in regards to the importance of BPG, decreasing the haemoglobin molecule's affinity for oxygen, was in the human foetus, which in order to extract necessary oxygen from its mother, requires for its haemoglobin to have a greater oxygen affinity, and as such, the beta subunit, is replaced by a gamma subunit.

The only difference between the two, lies in the fact that the gamma subunit does not allow for the binding of BPG, and thus allows for a higher affinity for oxygen. However, as human beings mature, and as we enter this world, becoming self- sufficient in our respiratory processes, BPG becomes necessary, in order for haemoglobin to release its oxygen, in the necessary quantities to the tissues.

Clearly, at some stage in development, the gamma subunits, must be converted to beta subunits. Firstly, I ask, how does this process take place? Is it a direct conversion, between the two forms through the actions of an enzyme, or is it a modification in the production agent of haemoglobin? Secondly, at what stage in development (in terms of time) does this change generally occur? As always any help in the matter, would be most appreciated!

[Mokele]

All Hail Wikipedia!

 

The alpha, beta, and gamma subunits are all individual proteins, each coded by a separate gene. Thus one is never turned into the other, but rather the transcription of the gamma gene is lowered and eventually shut off, while the transcription of the beta gene is increased to replace it. Apparently this happens at around 6 months after birth.