Figure 5.

Key metabolic pathways of glycolysis, fermentation and electron transfer to nicotinamide adenine dinucleotide phosphate (NAD(P)⁺) cofactors in Clostridium cellulolyticum. L-Malate dehydrogenase (MDH) catalyzes the NADH-dependent reduction of oxaloacetate (OAA), forming the L-malate intermediate, and malic enzyme catalyzes the NADP⁺-dependent oxidation and decarboxylation of the intermediate to produce pyruvate and NADPH. In a second transhydrogenase system, isocitrate dehydrogenase catalyzes 2-oxoglutarate (2OG) and NADPH formation, while a putative 2-oxoacid dehydrogenase could catalyze the NADH-dependent formation of 2-hydroxyglutarate (2HG). Ferredoxin (Fd) reduced by the pyruvate:ferredoxin oxidoreductase enzyme can be oxidized to produce H₂ or coupled to the NADH-dependent reduction of NADP⁺ catalyzed by the iron-sulfur flavoprotein complex NfnAB. Fermentation products are shown in green, and electron transfer cofactors are shown in blue.