MainThe pore-forming α-subunits of voltage-gated potassium channels of the KV1 and KV4 families partner with non-membrane-integral β-subunits1,2,3,4,5 whose sequences exhibit puzzling similarity with aldo-keto reductases6,7—enzymes that reduce carbonyls to alcohols via the coupled oxidation of an NADPH cofactor. The isolated β-subunits show weak reductase activity towards a range of model aldehydes in vitro18,19, relying on NADPH as the electron donor, but whether, on which native carbonyls, and...