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

Abstract

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 α-ketoglutarate were the strongest inhibitors. The physiological roles of PEP carboxylase and malic enzyme in Z. mobilis are discussed.