Autotrophic Carbon Dioxide Fixation

Ribulosebisphosphate carboxylase [Carboxy-dismutase] (4.1.1.39) is present. Glyceraldehyde-phosphate dehydrogenase (NADP ) 

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Autotrophic microorganisms synthesize organic substances from carbon dioxide through a process known as carbon dioxide fixation. They are important in nature because carbon dioxide fixation works as a precursor for the organic substrates that form the basis of the food chain for other organisms. Autotrophic bacteria include those that obtain their energy from light (photoautotrophs) and those that obtain it from the oxidation of chemical bonds (chemoau-totrophs). 

Carbon Dioxide, Fixation by Heterotrophs and Autotrophs (Utter... 

The catalysis of the transfer of a methyl group is an important role of enzyme-bound vitamin B12 derivatives in human, animal, and bacterial metabolism. The known enzyme-controlled methyl group-transfer reactions are key steps in the cobamide-dependent methylations of homocysteine to methionine, in the metabolic formation of methane from other Ci-compounds in methanogenic bacteria, and in the fixation of carbon dioxide via the acetyl coenzyme A pathway of some bacterial autotrophs (Figure 10). ... 

Reaction 2 above shows the reductive formation of acetate from CO2. This occurs via the acetyl-CoA pathway so called beeause the acetyl group of acetyl-CoA is the first 2-carbon moiety in which both carbons originate from CO2. The acetyl-CoA pathway is now recognized as an autotrophic pathway of CO2 fixation. The pathway is outlined in Fig. 1. Carbon dioxide enters the pathway via two reductive reactions. One, catalyzed by an NADP-dependent formate hydrogenase (FDH), leads to the formation of formate that, in a series of reaetions involving tetrahydrofolate (THF)intermediates is reduced to methyl-THF, the methyl group of which is... 

Autotrophs, Fixation of Carbon Dioxide by (Utter and Wood) XII 41... 

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