This is the first committed step in the biosynthesis of lipoyl cofactor. Lipoylation is essential for the function of several key enzymes involved in oxidative metabolism, as it converts apoprotein into the biologically active holoprotein. Examples of such lipoylated proteins include pyruvate dehydrogenase (E2 domain), 2-oxoglutarate dehydrogenase (E2 domain), the branched-chain 2-oxoacid dehydrogenases and the glycine cleavage system (H protein) [2,3]. Lipoyl-ACP can also act as a substrate  although octanoyl-ACP is likely to be the true substrate . The other enzyme involved in the biosynthesis of lipoyl cofactor is EC 22.214.171.124, lipoyl synthase. An alternative lipoylation pathway involves EC 126.96.36.199, lipoate---protein ligase, which can lipoylate apoproteins using exogenous lipoic acid (or its analogues).