Catalyzes the transfer of endogenously produced octanoic acid from octanoyl-acyl-carrier-protein onto the lipoyl domains of lipoate-dependent enzymes. Lipoyl-ACP can also act as a substrate although octanoyl-ACP is likely to be the physiological substrate (By similarity). L-lysyl-[protein] + octanoyl-[ACP] = H(+) + holo-[ACP] + N(6)-octanoyl-L-lysyl-[protein] Protein modification; protein lipoylation via endogenous pathway; protein N(6)-(lipoyl)lysine from octanoyl-[acyl-carrier-protein]: step 1/2. In the reaction, the free carboxyl group of octanoic acid is attached via an amide linkage to the epsilon-amino group of a specific lysine residue of lipoyl domains of lipoate-dependent enzymes. Belongs to the LipB family.