Editing Lipoic acid (section)

===Biosynthesis and attachment===
Most endogenously produced RLA are not "[[Free fatty acid|free]]" because octanoic acid, the [[Precursor (chemistry)|precursor]] to RLA, is bound to the enzyme complexes prior to enzymatic insertion of the sulfur atoms. As a cofactor, RLA is [[Covalent bond|covalently]] attached by an [[amide bond]] to a terminal [[lysine]] [[Residue (chemistry)#Biochemistry|residue]] of the enzyme's lipoyl [[Protein domain|domains]].
The precursor to lipoic acid, [[octanoic acid]], is made via [[Mitochondrial fatty acid synthesis|mitochondrial fatty acid biosynthesis]] in the form of octanoyl-[[acyl carrier protein]].<ref name=lpi/> The octanoate is transferred as a [[thioester]] of [[acyl carrier protein]] from mitochondrial fatty acid biosynthesis to an [[amide]] of the lipoyl domain protein by an [[enzyme]] called an [[Lipoyl(octanoyl) transferase|octanoyltransferase]].<ref name=lpi/> Two [[Hydrogen|hydrogens]] of octanoate are replaced with sulfur groups via a [[radical SAM]] mechanism, by [[lipoyl synthase]].<ref name=lpi/> As a result, lipoic acid is synthesized attached to proteins and no free lipoic acid is produced. Lipoic acid can be removed whenever proteins are degraded and by action of the enzyme [[lipoamidase]].<ref>{{cite journal |last1= Jiang |first1= Y |last2= Cronan |first2= JE |year= 2005 |title= Expression cloning and demonstration of ''Enterococcus faecalis'' lipoamidase (pyruvate dehydrogenase inactivase) as a Ser-Ser-Lys triad amidohydrolase |journal= [[Journal of Biological Chemistry]] |volume= 280 |issue= 3 |pages= 2244–56 |pmid= 15528186 |doi= 10.1074/jbc.M408612200 |doi-access= free }}</ref> Free lipoate can be used by some organisms as an enzyme called [[lipoate protein ligase]] that attaches it covalently to the correct protein. The [[ligase]] activity of this [[enzyme]] requires [[Adenosine triphosphate|ATP]].<ref>{{cite book |last1= Cronan |first1= JE |title= Function, attachment and synthesis of lipoic acid in ''Escherichia coli'' |last2= Zhao |first2= X |last3= Jiang |first3= Y  |year= 2005 |series= Advances in Microbial Physiology |volume= 50 |pages= 103–46 |pmid= 16221579 |doi= 10.1016/S0065-2911(05)50003-1 |isbn= 9780120277506 |editor-first= RK |editor-last= Poole}}
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