Required for respiration and the maintenance of the mitochondrial compartment. Oxidoreductase with a preference for short and medium chain substrates, including trans-2-hexenoyl-CoA (C6), trans-2-decenoyl-CoA (C10), and trans-2-hexadecenoyl-CoA (C16). May play a role in mitochondrial fatty acid synthesis. a 2,3-saturated acyl-[ACP] + NADP(+) = a (2E)-enoyl-[ACP] + H(+) + NADPH Homodimer and heterodimer with ETR1. Up-regulated by growth on oleic acid. Belongs to the zinc-containing alcohol dehydrogenase family. Quinone oxidoreductase subfamily.