ISSN:
1432-072X
Keywords:
Hydrogenobacter thermophilus
;
Autotrophic CO2 assimilation
;
The reductive tricarboxylic acid cycle
;
Pyruvate carboxylase
;
Phosphoenolpyruvate synthetase
;
ATP citrate lyase
;
Fumarate reductase
;
Pyruvate synthase
;
α-Ketoglutarate synthase
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The incorporation of 14CO2 by the cell suspensions of an extremely thermophilic, aerobic hydrogen-oxidizing bacterium, Hydrogenobacter thermophilus was studied. After short time incubation of the cell suspensions with 14CO2, the radiactivity was initially present in aspartate, glutamate, succinate, phosphorylated compounds, citrate, malate and fumarate. All of these compounds except phosphorylated compounds were related to the members of the tricarboxylic acid cycle. The proportion of labelled aspartate onglutamate in total radioactivity on each chromatogram decreased with incubation time, while the percentage of the radioactivity incorporated in phosphorylated compounds increased with time up to 10 s. These indicated that aspartate and glutamate is derived from primary products of CO2 fixation. In cell-free extracts of Hydrogenobacter thermophilus, the two key enzymes in the Calvin cycle, ribulose-1,5-bisphosphate carboxylase and phosphoribulokinase could not be detected. The key enzymes of the reductive tricarboxylic acid cycle, fumarate reductase and ATP citrate lyase were present. Activities of phosphoenolpyruvate synthetase and pyruvate carboxylase were also detected. The referse reactions (dehydrogenase reactions) of α-ketoglutarate synthase and pyruvate synthase could be detected by using methyl viologen as an electron acceptor. These findings strongly suggested that a new type of the reductive tricarboxylic acid cycle operated as the CO2 fixation pathway in Hydrogenobacter thermophilus.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00408058
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