A Japanese research team involving Osaka University investigated biliverdin reductase, the enzyme producing bilirubin – a substance linked with jaundice – from biliverdin (BV). Two BV molecules were found at the enzyme reaction site, in an unusual stacked arrangement. Mutation experiments confirmed which enzyme amino acid was necessary for bilirubin production. In the proposed mechanism, this amino acid transfers hydrogen to one BV molecule, using the other BV as a conduit. This aids the search for anti-jaundice drugs.