Oxygene entry into cells

[Francis Durst]

In article <01bd3d4b$40eda6c0$df80808f at bchm7.bch.unp.ac.za> "che" <pillayc at biochem.unp.ac.za> writes:
>From: "che" <pillayc at biochem.unp.ac.za>
>Subject: Oxygene entry into cells
>Date: 19 Feb 1998 15:28:47 GMT

>Hello All,

>Whilst I know that oxygen is delivered to cells by haemoglobin, how does
>this oxgen enter the cells ?  Is this oxygen chanelled to the mitochondria
>by intracellular carrier molecules ?  Why does this oxygen not react with
>cellular reducing agents (like glutathione) which are present at high
>concentrations in the cytoplasm.  Oxygen (O2) is a non-polar molecule, why
>should it dissolve into the cytoplasmic mileu when it could easily dissolve
>into the lipid bilayer ?  If this is the case, would there not be a chance
>of fatty acid oxidation ?

>Any references would be greatly appreciated.

>Che Pillay

Hi Che,

I think the reaction of O2 with organic molecules is spin-hindred: O2 is 
triplet while most organics are singlet, this is basically why, although we 
are made of mostly reduced organic matter, we do not burst in flames (even at 
spring time when the  activation energy of the younger ones is at peak 
level!).  In a poetic way (the 'real' chemists will balk) you may envisaged 
it as follows:O2 is a diradical with two electrons with parallel spin, so for 
it to insert in say a C-H bond, one spin has to reverse, which takes more time 
than the rapid contact when O2 bounces into an organic molecule. So the 
reaction is kinetically unfavored, but of course occurs at a low rate (butter 
becoming rancid etc...). 
To react, O2 has to be activated, which is what all oxygenases (and 
hemoglobin) do, by binding to a transition metal, or as a flavin 
hydroperoxide. 

And O2 IS soluble at a few ppm (depending on temp) in water and cytoplasm 
which is well enough to diffuse to the reaction centers.

All the best

Francis
===============================================================
Francis Durst, IBMP
Strasbourg, France