Catalyzes the conversion of crotonyl-CoA to butyryl-CoA. It uses only NADP as electron donor. May have a role in providing butyryl-CoA as a starter unit for straight-chain fatty acid biosynthesis. butanoyl-CoA + NADP(+) = (2E)-butenoyl-CoA + H(+) + NADPH Inhibited by NADPH at concentrations above 200 uM, by MgCl (30%), by ZnCl(2) (55%), and by CoCl, MnCl and CaCl (100%). Also inhibited by iodoacetamide, N-ethylmaleamide, the thiol group inhibitor beta-chloromercuribenzoate, palmitoyl-CoA and myristoyl-CoA. Optimum pH is 6.5. Optimum temperature 40 degrees Celsius. Homodimer. Belongs to the zinc-containing alcohol dehydrogenase family. Crotonyl-CoA carboxylase/reductase subfamily.