Operation of glyoxylate cycle in halophilic archaea: presence of malate synthase and isocitrate lyase in Haloferax volcanii

Abstract

The occurrence of the glyoxylate cycle has not previously been demonstrated in any of the Archaea. In halophilic archaea, only isocitrate lyase activity has been detected. The halophilic archaeon Haloferax volcanii was tested for the presence of the other key enzyme of this pathway, malate synthase. High activities of this enzyme were detected when the carbon source was acetate. Both glyoxylate cycle key enzymes, isocitrate lyase and malate synthase, from Hf. volcanii were purified and characterized.z 1998 Federation of European Biochemical Societies.

The methylaspartate cycle in haloarchaea and its possible role in carbon metabolism

“…This means that isocitrate lyase and isocitrate dehydrogenase directly compete for isocitrate. The kinetic parameters of isocitrate dehydrogenase are normally better than those of isocitrate lyase: for example, the Haloferax volcanii enzymes have the K m value to isocitrate of 0.13 and 1.16 mM, respectively (Camacho et al, 1995;Serrano et al, 1998). Therefore, the functioning of isocitrate lyase in the presence of isocitrate dehydrogenase requires a large pool of isocitrate, overproduction of isocitrate lyase, or complicated regulation mechanisms controlling isocitrate dehydrogenase activity like, for example, phosphorylation in enterobacteria (El-Mansi et al, 1994;Cozzone and El-Mansi, 2005).…”

Biochemical Analysis of Halophilic Dehydrogenases Altered by Site-Directed Mutagenesis

“…However, it has been shown that some halophilic archaea are able to use not only amino acids but different metabolites as well, as, for example, Haloferax mediterranei, which grows in a minimal medium containing glucose as the only source of carbon using a modified Entner-Doudoroff pathway (Rodriguez-Valera et al, 1983), or Haloferax volcanii, which is also able to grow in minimal medium with acetate as the sole carbon source (Kauri et al, 1990). Isocitrate lyase and malate synthase activities were detected in this organism when it was grown on a medium with acetate as the main carbon source (Serrano et al, 1998).…”

Relationship between Glyoxylate Cycle and Nitrification Efficiency based on Heterotrophic Nitrification Bacterium Acinetobacter sp.Y1

“…Protein concentration was determined as described by Bradford [6,25], using boving serum albumin as standard.…”

“…The gloxylate cycle, which was first proposed by Kornberg and Krebs [1,2] in bacteria growing on acetate [3], is an anaplerotic metabolic pathway which plays an important role in the biogenesis of carbohydrates from C2 compounds [4,5].There are alternative pathways to the glyoxylate cycle in some bacteria [6][7][8].This pathway is widespread in living organisms (Bacteria, Eukarya and Archaea), and the two key enzymes (isocitrate lyase and malate synthase) have been detected in various eubacteria, fungi, plants and even some animals [4,6].…”

“…Dixon and Kornberg were the first to demonstrate the occurrence of the two key enzymes [9,10]. Isocitrate lyase, catalyzing the cleavage of D-isocitrate to glyoxylate and succinate; and malate synthase, catalyzing the formation of L-malate from glyoxylate and acetyl-CoA [6].The gloxylate cycle contributes the formation of a C4 compound from two acetyl-CoA (C2) molecules in each cycle [6].…”