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Nadide Torun

Fatty Acid Synthesis

picture 1 (left upper corner) is the FAS or fatty acid synthase. It's the multifunctional proteïn that has all the necessary enzymes in one complex consisting of 2 monomers. (And for example; CE is the condensing enzyme). Picture 2 (at the right) is the steps you do when you are at the reduction part (green part on picture 1) And picture 3 (left bottom corner) is another scheme that shows the condensation, reduction and translocation and so on. This last picture confuses me a little.

I have a problem in my reasoning on the fatty acid synthesis in the human body.In the synthesis process you have this homodimer.

So the synthesis starts with the transfer of a acetyl group from acetyl-CoA to the sulfhydrylgroup of the condensing enzyme (CE) with help of the acetyltransferase enzyme (AT) and this on 1 of the 2 monomers.

At the same time a malonyl group from malonyl-CoA is transfered to the sulfhydryl terminus of phosphopantotheine from the ACP, and this on the other monomer and with help of the malonyltransferase (MT) enzyme.

AND HERE THE PROBLEM STARTS

The acetyl residue will be condensing with the malonylACP and at the same time there will be a decarboxylation (CO2 goes off) and CE goes off from acetyl. At the end acetoacetyl-ACP is formed. So if I got it right; the acetyl residue is being 'cut off' from the CE from the first monomere and binds to the malonylACP on the other monomere. Right?

And after that the acetoacetyl-ACP will be swept back to the other monomer (to the reduction part), is this also right?

Then the reduction-dehydration-reduction steps are happening and at the end of the road you will get butyryl-ACP which will cut off from the ACP and migrate on the same monomer to the cysteine residue at the condensing enzyme (CE) (= translocation).

And after that you can start a new condensation-reduction-translocation cycle and go on until you end up at palmitoyl-ACP.

So the actual question is; is my reasoning right about how the product is going from one monomer to the other several times?In my book it's a pretty messy explanation and so I want to be sure I'm right.

I hope somebody can help me out =)

Greetings

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