D-Glucuronic acid is a biomass component that occurs in plant cell wall polysaccharides and is catabolized by saprotrophic microorganisms including fungi. A pathway for D-glucuronic acid catabolism in fungal microorganisms is only partly known. In the filamentous fungus , the enzymes that are known to be part of the pathway are the NADPH requiring D-glucuronic acid reductase forming L-gulonate and the NADH requiring 2-keto-L-gulonate reductase that forms L-idonate. With the aid of RNA sequencing we identified two more enzymes of the pathway. The first is a NADPH requiring 2-keto-L-gulonate reductase that forms L-idonate, GluD. The second is a NAD requiring L-idonate 5-dehydrogenase forming 5-keto-gluconate, GluE. The genes coding for these two enzymes are clustered and share the same bidirectional promoter. The GluD is an enzyme with a strict requirement for NADP/NADPH as cofactors. The k for 2-keto-L-gulonate and L-idonate is 21.4 and 1.1 s, and the K 25.3 and 12.6 mM, respectively, when using the purified protein. In contrast, the GluE has a strict requirement for NAD/NADH. The k for L-idonate and 5-keto-D-gluconate is 5.5 and 7.2 s, and the K 30.9 and 8.4 mM, respectively. These values also refer to the purified protein. The deletion resulted in accumulation of 2-keto-L-gulonate in the liquid cultivation while the deletion resulted in reduced growth and cessation of the D-glucuronic acid catabolism.