Figure 2.

Fermentation of glucose to generate butyrate. Schematic of key metabolic pathways for hydrogen production in Clostridium acetobutylicum. Arrows with larger width indicate a series of reactions. Arrows with narrow width indicate individual reactions. Enzymes: 1, glycolytic enzymes; 2, pyruvate ferredoxin oxidoreductase (E.C. 1.2.7.1); 3, hydrogenase (E.C.1.12.7.2); 4, acetyl-CoA acetyltransferase (thiolase) (E.C. 2.3.1.9); 5, β-hydroxybutyryl-CoA dehydrogenase (E.C. 1.1.1.157); 6, crotonase (E.C. 4.2.1.55); 7, butyryl-CoA dehydrogenase (E.C. 1.3.99.2); 8, phosphotransbutyrylase (E.C.2.3.1.19); 9, butyrate kinase (E.C. 2.7.2.7). Abbreviations: Ferredoxin (Fd); Coenzyme A (CoASH).