This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Generation of Precursor Metabolites and Energy → Acetyl-CoA Biosynthesis|
Some taxa known to possess this pathway include : Euglena gracilis
Expected Taxonomic Range: Euglenozoa
The conversion of pyruvate to acetyl-CoA and CO2 is a key reaction of central metabolism, which links the substrate-level phosphorylation glycolysis pathway (which ends with the generation of pyruvate) to the TCA cycle, which accepts the input of acetyl-CoA. In addition, acetyl-CoA is a substrate for many biosynthetic processes.
Most eukaryotes perform the oxidative decarboxylation of pyruvate in mitochondria using the NAD+-dependent pyruvate dehydrogenase complex (PDH). Eukaryotes that lack mitochondria use instead the oxygen-sensitive enzyme pyruvate:ferredoxin oxidoreductase (PFO), which is localized either in the cytosol or in hydrogenosomes.
The mitochondrion of the photosynthetic protist Euglena gracilis is a facultatively anaerobic organelle that produces ATP in the presence and absence of oxygen. However, unlike typical mitochondria it does not use the PDH system but the unusual oxygen-sensitive, NADP-dependent pyruvate dehydrogenase (PNO) for the oxidative decarboxylation of pyruvate [Inui84, Inui87].
Under aerobiosis, acetyl-CoA from PNO enters a modified Krebs cycle, which drives oxidative phosphorylation using O2 as the terminal electron acceptor.
Under anaerobiosis, PNO is the key enzyme of a unique wax ester fermentation. Acetyl-CoA from PNO is used both as primer and as C2-donor for fatty acid synthesis in mitochondria, consuming the electrons that originate from glucose breakdown.The fatty acids are reduced and esterified to form waxes that are stored in the cytosol. Upon return to aerobic conditions, the waxes are utilized via β-oxidation and oxidative phosphorylation [Inui85, Rotte01]
Inui84: Inui H, Miyatake K, Nakano Y, Kitaoka S (1984). "Occurrence of oxygen-sensitive, NADP+-dependent pyruvate dehydrogenase in mitochondria of Euglena gracilis." J Biochem 96(3);931-4. PMID: 6438078
Inui85: Inui H, Miyatake K, Nakano Y, Kitaoka S (1985). "The physiological role of oxygen-sensitive pyruvate dehydrogenase in mitochondrial fatty acid synthesis in Euglena gracilis." Arch Biochem Biophys 237(2);423-9. PMID: 3919646
Rotte01: Rotte C, Stejskal F, Zhu G, Keithly JS, Martin W (2001). "Pyruvate : NADP+ oxidoreductase from the mitochondrion of Euglena gracilis and from the apicomplexan Cryptosporidium parvum: a biochemical relic linking pyruvate metabolism in mitochondriate and amitochondriate protists." Mol Biol Evol 18(5);710-20. PMID: 11319255
Nakazawa00: Nakazawa M, Inui H, Yamaji R, Yamamoto T, Takenaka S, Ueda M, Nakano Y, Miyatake K (2000). "The origin of pyruvate: NADP+ oxidoreductase in mitochondria of Euglena gracilis." FEBS Lett 479(3);155-6. PMID: 11023353
Rubio06: Rubio S, Larson TR, Gonzalez-Guzman M, Alejandro S, Graham IA, Serrano R, Rodriguez PL (2006). "An Arabidopsis mutant impaired in coenzyme A biosynthesis is sugar dependent for seedling establishment." Plant Physiol 140(3);830-43. PMID: 16415216
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