Catalyzes the NADPH-dependent reduction of trans-2-enoyl thioesters in mitochondrial fatty acid synthesis (fatty acid synthesis type II). Fatty acid chain elongation in mitochondria uses acyl carrier protein (ACP) as an acyl group carrier, but the enzyme accepts both ACP and CoA thioesters as substrates in vitro. Required for respiration and the maintenance of the mitochondrial compartment. a 2,3-saturated acyl-[ACP] + NADP(+) = a (2E)-enoyl-[ACP] + H(+) + NADPH (2E,4E)-hexadienoyl-CoA + H(+) + NADPH = (4E)-hexenoyl-CoA + NADP(+) (2E)-hexenoyl-CoA + H(+) + NADPH = hexanoyl-CoA + NADP(+) Homodimer or in a complex with other proteins (PubMed:11509667). Interacts with ARS1 (PubMed:8195160). Positively regulated by the zinc-responsive transcriptional regulator ZAP1. Present with 1560 molecules/cell in log phase SD medium. Belongs to the zinc-containing alcohol dehydrogenase family. Quinone oxidoreductase subfamily. Was originally (PubMed:8195160) thought to be a nuclear protein involved in transcriptional regulation of genes required for the functional assembly of mitochondrial respiratory proteins. This was later proven not to be the case (PubMed:11509667).