title: The 2-oxoacid dehydrogenase multienzyme complex of Haloferax volcanii.
abstract: Those aerobic archaea whose genomes have been sequenced possess four adjacent genes that, by sequence comparisons with bacteria and eukarya, appear to encode the component enzymes of a 2-oxoacid dehydrogenase multienzyme complex. However, no catalytic activity of any such complex has ever been detected in the archaea. In Thermoplasma acidophilum, evidence has been presented that the heterologously expressed recombinant enzyme possesses activity with the branched chain 2-oxoacids and, to a lesser extent, with pyruvate. In the current paper, we demonstrate that in Haloferax volcanii the four genes are transcribed as an operon in vivo. However, no functional complex or individual enzyme, except for the dihydrolipoamide dehydrogenase component, could be detected in this halophile grown on a variety of carbon sources. Dihydrolipoamide dehydrogenase is present at low catalytic activities, the level of which is increased three to fourfold when Haloferax volcanii is grown on the branched-chain amino acids valine, leucine and isoleucine.
authors.affiliation: Department of Biological Sciences, Faculty of Science, Kuwait University, PO Box 5969, Safat 13060, State of Kuwait.
authors.forename: Dina M
authors.initials: DM
authors.lastname: Al-Mailem
authors.forename: David W
authors.initials: DW
authors.lastname: Hough
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Danson
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D000597:Amino Acids, Branched-Chain / Q000378:metabolism*; D019843:Archaeal Proteins / Q000235:genetics / Q000378:metabolism*; D008058:Dihydrolipoamide Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D019766:Genes, Archaeal / Q000502:physiology; D019622:Haloferax volcanii / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D009876:Operon / Q000502:physiology; D013822:Thermoplasma / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D014158:Transcription, Genetic / Q000502:physiology
chemical_list: D000597:Amino Acids, Branched-Chain; D019843:Archaeal Proteins; D000445:Aldehyde Oxidoreductases; D008058:Dihydrolipoamide Dehydrogenase