Re -Citrate Synthase from Clostridium kluyveri Is Phylogenetically Related to Homocitrate Synthase and Isopropylmalate Synthase Rather Than to Si -Citrate Synthase

Abstract

The synthesis of citrate from acetyl-coenzyme A and oxaloacetate is catalyzed in most organisms by a Si-citrate synthase, which is Si-face stereospecific with respect to C-2 of oxaloacetate. However, in Clostridium kluyveri and some other strictly anaerobic bacteria, the reaction is catalyzed by a Re-citrate synthase, whose primary structure has remained elusive. We report here that Re-citrate synthase from C. kluyveri is the product of a gene predicted to encode isopropylmalate synthase. C. kluyveri is also shown to contain a gene for Si-citrate synthase, which explains why cell extracts of the organism always exhibit some Si-citrate synthase activity.

Investigation of Carbon Metabolism in “ Dehalococcoides ethenogenes ” Strain 195 by Use of Isotopomer and Transcriptomic Analyses

“…An oxygen sensitive Recitrate synthase (EC 2.3.3.3) was recently discovered in Clostridium kluyveri CKL0973, as well as in some Desulfovibrio spp. (17). When protein sequences of CKL0973 were compared to the strain 195 genome (www.jgi.doe.gov) using BLASTP (3), the resulting highest polypeptide amino acid sequence identity was very low: 28% for homocitrate synthase (DET1614) and 22% for 2-isopropylmalate synthase (LeuA, DET0830).…”

The genome ofClostridium kluyveri, a strict anaerobe with unique metabolic features

“…The energy metabolism has been subject to many investigations (5,6,13), but its understanding, especially the mechanism of H 2 formation via ferredoxin from NADH, has remained a challenge until today because this is thermodynamically an uphill reaction requiring energy to proceed. Likewise, carbon assimilation by this organism has been studied, and novel enzymes and pathways were discovered (15)(16)(17). The organism has been used in the past as a source of enzymes, e.g., phosphotransacetylase for analytical purposes and enoate reductases for stereospecific hydrogenation reactions.…”

Dethiosulfatarculus sandiegensis gen. nov., sp. nov., isolated from a methanogenic paraffin-degrading enrichment culture and emended description of the family Desulfarculaceae

“…The genome lacked citrate synthase. However, it contains a re-citrate synthase that catalyses the formation of citrate from acetyl-CoA and oxaloacetate (Gottschalk & Barker, 1966;Kim et al, 2013;Li et al, 2007). Interestingly, re-citrate synthase is oxygensensitive and thus can only be found in anaerobic organisms.…”