Mechanistic Investigations of Lipoic Acid Biosynthesis in Escherichia coli: Both Sulfur Atoms in Lipoic Acid are Contributed by the Same Lipoyl Synthase Polypeptide

Lipoyl synthase catalyzes the final step in the de novo biosynthesis of the lipoyl cofactor, which is the insertion of two sulfur atoms into an octanoyl chain that is bound in an amide linkage to a conserved lysine on a lipoyl-accepting protein. We show herein that the sulfur atoms in the lipoyl cofactor are derived from lipoyl synthase itself, and that each lipoyl synthase polypeptide contributes both of the sulfur atoms to the intact cofactor.