Lipoate (lipoic acid) is a lipidic cofactor covalently attached to a lysine of ppl, a subunit of the glycine cleavage complex and the E2 subunits Dlat of the pyruvate dehydrogenase complex, Dlst of the oxoglutarate and oxoadipate dehydrogenase complexes and Dbct of the branched-chain alpha-ketoacid dehydrogenase complex. Lipoate biosynthesis occurs in the mitochondrion. It begins with the transfer of the octanoyl moiety from octanoyl-acyl-carrier protein (ND-ACP) onto ppl (H protein), followed by the attachment of two sulfur atoms at C6 and C8 of the octanoyl moiety prior to its transfer from ppl to the E2 subunits of the dehydrogenase complexes. (Adapted from PMID:29169048.)