Enoyl-ACP reductase of the type II fatty acid syntase (FAS-II) system, which is involved in the biosynthesis of mycolic acids, a major component of mycobacterial cell walls. Catalyzes the NADH-dependent reduction of the double bond of 2-trans-enoyl-[acyl-carrier protein], an essential step in the fatty acid elongation cycle of the FAS-II pathway. Shows preference for long-chain fatty acyl thioester substrates, and can also use 2-trans-enoyl-CoAs as alternative substrates. The mycobacterial FAS-II system utilizes the products of the FAS-I system as primers to extend fatty acyl chain lengths up to C56, forming the meromycolate chain that serves as the precursor for final mycolic acids. Is the primary target of the first-line antitubercular drug isoniazid (INH) and of the second-line drug ethionamide (ETH) (PubMed:12406221). Overexpressed inhA confers INH and ETH resistance to M.bovis (PubMed:12406221). The mechanism of isoniazid action against InhA is covalent attachment of the activated form of the drug to the nicotinamide ring of NAD and binding of the INH-NAD adduct to the active site of InhA (By similarity). Similarly, the ETH-NAD adduct binds InhA (By similarity). a 2,3-saturated acyl-[ACP] + NAD(+) = a (2E)-enoyl-[ACP] + H(+) + NADH a 2,3-saturated acyl-CoA + NAD(+) = a (2E)-enoyl-CoA + H(+) + NADH Lipid metabolism; mycolic acid biosynthesis. Homodimer. Homotetramer. Belongs to the short-chain dehydrogenases/reductases (SDR) family. FabI subfamily.