Junctions of catabolic and anabolic pathways in Zymomonas mobilis: phosphoenolpyruvate carboxylase and malic enzyme

Summary The synthesis of oxalacetate and malate in the ethanol-producing bacterium Zymomonas mobilis have been investigated. Cell-free extracts were examined for pyruvate carboxylase, phosphoenolpyruvate (PEP) carboxylase, PEP carboxytransphosphorylase, PEP carboxykinase, and malic enzyme, but only PEP carboxylase and nicotine adenine dinucleotide (NAD)-dependent malic enzyme activities could be detected. The PEP carboxylase, partially purified from extracts, was not affected by acetyl-coenzyme A. Intermediates of the tricarboxylic acid cycle and aspartate inhibited the enzyme competitively with PEP. Of these, citrate and -ketoglutarate were the strongest inhibitors. The physiological roles of PEP carboxylase and malic enzyme in Z. mobilis are discussed.Dedicated to Prof. Dr. A. Fiechter, ETH Zürich, on the occasion of his 65th birthday