The ‘true’ l-xylulose reductase of filamentous fungi identified in Aspergillus niger

l-Xylulose reductase is part of the eukaryotic pathway for l-arabinose catabolism. A previously identified l-xylulose reductase in Hypocrea jecorina turned out to be not the ‘true’ one since it was not upregulated during growth on l-arabinose and the deletion strain showed no reduced l-xylulose reductase activity but instead lost the d-mannitol dehydrogenase activity 17]. In this communication we identified the ‘true’ l-xylulose reductase in Aspergillus niger. The gene, lxrA (JGI177736), is upregulated on l-arabinose and the deletion results in a strain lacking the NADPH-specific l-xylulose reductase activity and having reduced growth on l-arabinose. The purified enzyme had a K_m for l-xylulose of 25 mM and a ν_max of 650 U/mg.