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RuBisCO is important biologically because it catalyzes the primary chemical reaction by which inorganic carbon enters the biosphere.While many autotrophic bacteria and archaea fix carbon via the reductive acetyl CoA pathway, the 3-hydroxypropionate cycle, or the reverse Krebs cycle, these pathways are relatively small contributors to global carbon fixation compared to that catalyzed by RuBisCO.
The reactive enodiolate species is also sensitive to oxygen (O 2), which results in the dual carboxylase / oxygenase activity of RuBisCO. [13] This reaction is considered wasteful as it produces products (3-phosphoglycerate and 2-phosphoglycolate) that must be catabolized through photorespiration. [14]
Notably pyruvate carboxylase consumes carbon dioxide (as bicarbonate ions) as part of gluconeogenesis, and carbon dioxide is consumed in various anaplerotic reactions. 6-phosphogluconate dehydrogenase catalyzes the reductive carboxylation of ribulose 5-phosphate to 6-phosphogluconate in E. coli under elevated CO 2 concentrations.
The resulting concentration of carbon dioxide near RuBisCO decreases the proportion of ribulose-1,5-bisphosphate oxygenation and thereby avoids costly photorespiratory reactions. The surrounding shell provides a barrier to carbon dioxide loss, helping to increase its concentration around RuBisCO. [4] [5] [6]
English: Carboxylation or oxygenation of ribulose-1,5-bisphosphate (1) to glycerate 3-phosphate (3) and/or 2-phosphoglycolate (4); this reactions are catalyzed by RuBisCO Deutsch: Carboxylierung oder Oxygenierung von Ribulose-1,5-bisphosphat (1) durch RuBisCO; dabei entsteht entweder Glycerat-3-phosphat (3) und/oder 2-Phosphoglycolat, was die ...
The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvin–Benson cycle, but approximately 25% of reactions by RuBisCO instead add oxygen to RuBP (oxygenation), creating a product that cannot be used within the Calvin–Benson cycle.
The light-independent reactions undergo the Calvin-Benson cycle, in which the energy from NADPH and ATP is used to convert carbon dioxide and water into organic compounds via the enzyme RuBisCO. The overall general equation for the light-independent reactions is the following: [11]
C 4 photosynthesis reduces photorespiration by concentrating CO 2 around RuBisCO. To enable RuBisCO to work in a cellular environment where there is a lot of carbon dioxide and very little oxygen, C 4 leaves generally contain two partially isolated compartments called mesophyll cells and bundle-sheath cells.