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Carbon Fixation

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Organisms that grow by fixing carbon are called autotrophs, which include photoautotrophs (which use sunlight), and lithoautotrophs (which use inorganic oxidation).
Organisms that grow by fixing carbon are called autotrophs, which include photoautotrophs (which use sunlight), and lithoautotrophs (which use inorganic oxidation).
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Seven autotrophic carbon fixation pathways are known.
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Several autotrophic carbon fixation pathways are known:
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'''Calvin cycle'''
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'''1) Calvin cycle'''
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3 CO<sub>2</sub> + 6 NADPH + 6 H<sup>+</sup> + 9 ATP + 5 H<sub>2</sub>O → glyceraldehyde-3-phosphate (G3P) + 6 NADP<sup>+</sup> + 9 ADP + 8 P<sub>i</sub> (P<sub>i</sub> = inorganic phosphate) (See also [https://en.wikipedia.org/wiki/Calvin_cycle])
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[[Calvin cycle]]
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''Step 1''
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'''2) Reverse Krebs cycle'''
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The enzyme [[RuBisCO]] catalyses the carboxylation of <scene name='94/942630/Cv/1'>ribulose-1,5-bisphosphate</scene>, RuBP, a 5-carbon compound, by carbon dioxide (a total of 6 carbons) in a two-step reaction. The product of the first step is enediol-enzyme complex that can capture CO2 or O2. Thus, enediol-enzyme complex is the real carboxylase/oxygenase. The CO2 that is captured by enediol in second step produces an unstable six-carbon compound called 2-carboxy 3-keto 1,5-biphosphoribotol (CKABP) (or 3-keto-2-carboxyarabinitol 1,5-bisphosphate) that immediately splits into 2 molecules of <scene name='39/392339/Cv1/6'>3-phosphoglycerate</scene>, a 3-carbon compound.
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[[Reverse Krebs cycle]]
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*[[RuBisCO]]
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*[[Rubisco and Crop Output]]
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*[[RuBisCO (Hebrew)]]
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''Step 2''
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'''3) Reductive acetyl CoA pathway'''
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The enzyme [[Phosphoglycerate Kinase|phosphoglycerate kinase]] catalyzes the phosphorylation of 3-PGA by ATP (which was produced in the light-dependent stage). <scene name='39/392339/Cv1/5'>1,3-Bisphosphoglycerate</scene> (glycerate-1,3-bisphosphate) and ADP are the products.
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[[Reductive acetyl CoA pathway]]
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''Step 3''
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'''4) 3-Hydroxypropionate bicycle'''
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The enzyme glyceraldehyde 3-phosphate dehydrogenase catalyses the reduction of 1,3BPGA by NADPH (which is another product of the light-dependent stage). Glyceraldehyde 3-phosphate (also called G3P, GP, TP, PGAL, GAP) is produced, and the NADPH itself is oxidized and becomes NADP+. Again, two NADPH are utilized per CO2 fixed.
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[[3-Hydroxypropionate bicycle]]
</StructureSection>
</StructureSection>
== References ==
== References ==
<references/>
<references/>

Current revision

Spinach RuBisCO 8 large and 8 small chains complex with substrate ribulose-1,5- bisphosphate, 1rcx

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References

Proteopedia Page Contributors and Editors (what is this?)

Alexander Berchansky

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