Identification of reaction products by LC-MS analysis. LC-MS analyses were carried out using reaction products with reconstituted TK2109 protein (A), reconstituted TK2248 protein (B), reconstituted TK2109 and TK2248 proteins (C), and nonreconstituted TK2109 and TK2248 proteins (D). Blue, red, green, and black lines represent the compounds whose m/z values corresponded to exact masses of octanoyl-peptide, lipoyl-peptide, reduced lipoyl-peptide, and intermediate thiol-octanoyl-peptide, respectively. Pep and RA, peptide and relative abundance, respectively.