The Citric Acid Cycle and Fatty Acid Biosynthesis

Abstract

This chapter talks about fatty acid biosynthesis, linked to the citric acid cycle (CAC) through the utilization of acetyl-coenzyme A (CoA) as its starting point. The oxidative decarboxylation of pyruvate is an important reaction in archaea, bacteria, and eukaryotes alike, generating acetyl-CoA necessary for CAC reactions, fatty acid biosynthesis, and many other reactions requiring acyl-CoA. Citrate synthase catalyzes the first step in the oxidative branch of the CAC in which acetyl-CoA and oxaloacetate are condensed to generate citrate and CoA. Aconitase activity has been detected in the cytosolic fraction of Helicobacter pylori cells both by nuclear magnetic resonance (NMR) and spectrophotometric assays. In Escherichia coli isocitrate dehydrogenase acts as a critical branch point between the CAC reactions and the glyoxylate bypass during growth on C2 compounds like acetate. The study of the lipid and fatty acid profiles of eight Helicobacter species has revealed some characteristic features of the Helicobacter genus. Malonyl-acylcarrier protein (ACP) is required not only for initiation of fatty acid biosynthesis, but also for each subsequent round of elongation of the fatty acid chain. To function in fatty acid biosynthesis, the apo-ACP protein must first be activated by transfer of the 4'-phospho-pantotheine from CoA, and this reaction is predicted to be catalyzed by holo-ACP synthase, encoded by acpS in H. pylori.