An Energy-conserving Pyruvate-to-Acetate Pathway in Entamoeba histolytica

tica grown with bacteria produce H, and acetate while cells grown axenically produce neither. Aerobically, acetate is produced and 0, is consumed by amehae from either type of cells. Centrifuged extracts, 2.4 x 10” x g x min, from both types of cells contain pyruvate synthase (EC 1.2.7.1) and an acetate thiokinase which, together, form a system capable of converting pyruvate to acetate. Pyruvate synthase catalyzes the reaction: pyruvate + CoA + CO, + acetyl-CoA + b. Electron acceptors which function with this enzyme are FAD, FMN, riboflavin, ferredoxin, and methyl viologen, but not NAD or NADP. The amebal acetate thiokinase catalyzes the reaction acetyl-CoA + AIIP + P, ---) acetate + ATP + CoA. For this apparently new enzyme we suggest the trivial name acetyl-CoAsynthetase (AlIP-forming). Extracts from axenic amebae do not contain hydrogenase, but extracts from cells grown with bacteria do. It is postulated that in bacteria-grown amebae electrons generated at the pyruvate synthase step are utilized anaerobically to produce Hz via the hydrogenase and that the acetyl-CoA is converted to acetate in an energy-conserving step catalyzed by amebal acetyl-CoA-synthetase. Aerobically, cells grown under either regimen may utilize the energy-conserving pyruvateto-acetate pathway since 0, then serves as the ultimate electron acceptor.