NADPH-dependent 5-keto-D-gluconate reductase is a part of the fungal pathway for D-glucuronate catabolism.

NADPH-dependent 5-keto-D-gluconate reductase was identified as a missing element in the pathway for D-glucuronate catabolism in fungi. The disruption of the gene， gluF， by CRISPR/Cas9 in the filamentous fungus Aspergillus niger resulted in a strain unable to catabolise D-glucuronate. The purified GluF protein was characterized and k and K values of 23.7 ± 1.8 s and 3.2 ± 0.1 mm for 5-keto-D-gluconate， respectively， were determined. The enzyme is reversible and is active with NADP and D-gluconate. We suggest a pathway for D-glucuronate catabolism with the intermediates L-gulonate， 2-keto-L-gulonate， L-idonate， 5-keto-D-gluconate， D-gluconate and D-gluconate-6-phosphate which is a part of the pentose phosphate pathway. A fungal enzyme activity for the conversion of L-gulonate to 2-keto-L-gulonate remains to be identified.