he entire synthesis process which produces palmitic acid occurs on a multifunctional dimeric protein Fatty Acid Synthase (FA) in the cytosol. The production of palmitic acid can be summarized as the successive addition of two carbons to an initial acetyl moiety primer. After 7 cycles palimitic acid is released. The synthesis starts with the sequential transfer of a primer substrate, acetyl-CoA, to the nucleophilic serine residue of the acyltransferase domain of FA. The acetyl moiety is then transferred to the Acyl Carrier Protein (ACP) domain of FA, then finally to the active site of the beta-ketoacyl synthase domain. A chain extender substrate, molonyl-CoA, is transferred to the nucleophilic serine residue of the acyltransferase domain and subsequently to the ACP domain. The acetyl moiety is extend by a condensation reaction, catalysed by the beta-ketoacyl synthase domain, that produces a new Carbon-Carbon bound, this reaction is coupled to a decarboxylation resulting in the production of carbon dioxide. Subsequently beta-ketoacyl condensation product is reduced to a saturated acyl moiety through the step wise action on the beta-ketoacyl reductase, beta-hydroxyacyl dehydrase and enoyl reductase domains respectively. This saturated acyl moiety is then transfer back to the active site of the beta-ketoacyl synthase domain, another molonyl-CoA is loaded and the process repeats. The addition of molonyl moieties occurs 7 times after which the final product is released by that action of thioesterase domain. The final product is 16 carbon long palmitic acid.

Fatty Acid Biosynthesis References