Thermoproteus neutrophilus

The dicarboxylate/4-hydroxybutyrate cycle starts from acetyl-CoA, which is reductively carboxylated to pyruvate. Pyruvate is converted to PEP and then car-boxylated to oxaloacetate. The latter is reduced to succinyl-CoA by the reactions of an incomplete reductive citric acid cycle. Succinyl-CoA is reduced to 4-hydroxybu-tyrate, the subsequent conversion of which into two acetyl-CoA molecules proceeds in the same way as in the 3-hydroxypropionate/4-hydroxybutyrate cycle. The cycle can be divided into part 1 transforming acetyl-CoA, one C02 and one bicarbonate to succinyl-CoA via pyruvate, PEP, and oxaloacetate, and part 2 converting succinyl-CoA via 4-hydroxybutyrate into two molecules of acetyl-CoA. This cycle was shown to function in Igrticoccus hospitalis, an anaerobic autotrophic hyperther-mophilic Archaeum (Desulfurococcales) [40]. Moreover, this pathway functions in Thermoproteus neutrophilus (Thermoproteales), where the reductive citric acid cycle was earlier assumed to operate, but was later disproved (W.H. Ramos-Vera et al., unpublished results). 

AMP-dependent synthetases of eubacteria, eukaryotes, methanogens and Thermoproteus neutrophilus, where the enzyme is thought to function in the activation of acetate to acetyl-CoA (see ref. [1] and references therein). 

Strauss G, Eisenreich W, Bacher A, Fuchs G. (1992). C-NMR study of autotrophic COj fixation pathways in the sulfur-reducmg Archaebacterium Thermoproteus neutrophilus and in the phototrophic Euhacteiium Chloroflexus aurantiacus. Eur J Biochem, 205, 853-866. 

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