Acylcarnitine transferase II: where does the energy come from?

[Interprete]

Hello,

In ß-oxydation, when an activated fatty acid is shuttled from the cytosol into the mitochondria, it sheds a CoA-SH moiety and then regains another one once inside the mitochondria, through the acylcartinine transferase II. My question is: where does the energy to re-attach a new mitochondrial CoA to the fatty acid come from?

When it was activated in the cytosol by the acylCoA synthetase, it consumed one ATP. How comes it does not need an ATP again, for the same reaction once inside? Is it because acylcarnitine contains a high-energy bond that can provide the energy necessary to recreate the thioester bond to form acylCoA again?

 

Thanks...

[BabcockHall]

Although I think that the concept of a high energy bond can mislead the unwary, I think that you are on the right track.  The free energies of hydrolysis of esters vary quite a bit from one to another.  I don't have a table that provides this value for an acylcarnitine ester; however, my recollection is that it is relatively high in energy.

Edited October 21, 2017 by BabcockHall