Thioester tissue-specific

It is unclear how the synthesis of predominantly short-chain fatty acids occurs, especially as the fatty acid synthase from the uropygial gland appears to have the same characteristics as in other tissues. During the biosynthesis of fatty acids from malonyl-CoA and methylmalonyl-CoA by the fatty add synthase, the growing chain is attached to the pantotheine group of the multienzyme polypeptide by a thioester link. One of the enzyme activities associated with a domain of the multienzyme polypeptide is the thioesterase (reaction 4.4), which has a specificity for cleaving thioesters of longer chain fatty acids esterified to the acyl carrier protein (ACP). 

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