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A new hypothesis for the origin of eukaryotic cells is proposed, based on the comparative biochemistry of energy metabolism. Eukaryotes are suggested to have arisen through symbiotic association of an anaerobic, strictly hydrogen-dependent, strictly autotrophic archaebacterium (the host) with a eubacterium (the symbiont) that was able to respire, but(More)
Major insights into the phylogenetic distribution, biochemistry, and evolutionary significance of organelles involved in ATP synthesis (energy metabolism) in eukaryotes that thrive in anaerobic environments for all or part of their life cycles have accrued in recent years. All known eukaryotic groups possess an organelle of mitochondrial origin, mapping the(More)
The current paradigm of eukaryotic evolution is based primarily on comparative analysis of ribosomal RNA sequences. It shows several early-emerging lineages, mostly amitochondriate, which might be living relics of a progressive assembly of the eukaryotic cell. However, the analysis of slow-evolving positions, carried out with the newly developed slow-fast(More)
The gene coding for the acetyl-CoA synthetase (ADP-forming) from the amitochondriate eukaryote Giardia lamblia has been expressed in Escherichia coli. The recombinant enzyme exhibited the same substrate specificity as the native enzyme, utilizing acetyl-CoA and adenine nucleotides as preferred substrates and less efficiently, propionyl- and succinyl-CoA. N-(More)
To determine the localization of several enzymes in Tritrichomonas foetus, the axenic KV-1 strain was grown in Diamond's medium with bovine serum, homogenized in 0 .25 M su-crose, and subjected to analytical differential and isopycnic centrifugation. The fractions were assayed for their enzymatic composition and examined electron microscopically. NADH and(More)
The sequence of an alpha-proteobacterial genome, that of Rickettsia prowazekii, is a substantial advance in microbial and evolutionary biology. The genome of this obligately aerobic intracellular parasite is small and is apparently still undergoing reduction, reflecting gene losses attributable to its intracellular parasitic lifestyle. Evolutionary analyses(More)
Giardia intestinalis (syn. lamblia) is one of the most widespread intestinal protozoan pathogens worldwide, causing hundreds of thousands of cases of diarrhoea each year. Giardia is a member of the diplomonads, often described as an ancient protist group whose primitive nature is suggested by the lack of typical eukaryotic organelles (for example,(More)
Genomic or cDNA clones for the glycolytic enzyme enolase were isolated from the amitochondriate pelobiont Mastigamoeba balamuthi, from the kinetoplastid Trypanosoma brucei, and from the euglenid Euglena gracilis. Clones for the cytosolic enzyme were found in all three organisms, whereas Euglena was found to also express mRNA for a second isoenzyme that(More)
The phylogenetic relationships of amoebae are poorly resolved. To address this difficult question, we have sequenced 1,280 expressed sequence tags from Mastigamoeba balamuthi and assembled a large data set containing 123 genes for representatives of three phenotypically highly divergent major amoeboid lineages: Pelobionta, Entamoebidae, and Mycetozoa.(More)