Calvin cycle

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Chloroplast structure.svg
The internal structure of a chloroplast

The Calvin cycle, light-independent reactions, bio synthetic phase, dark reactions, or photosynthetic carbon reduction (PCR) cycle [1] of photosynthesis is a series of chemical reactions that convert carbon dioxide and hydrogen-carrier compounds into glucose. The Calvin cycle is present in all photosynthetic eukaryotes and also many photosynthetic bacteria. In plants, these reactions occur in the stroma, the fluid-filled region of a chloroplast outside the thylakoid membranes. These reactions take the products (ATP and NADPH) of light-dependent reactions and perform further chemical processes on them. The Calvin cycle uses the chemical energy of ATP and reducing power of NADPH from the light dependent reactions to produce sugars for the plant to use. These substrates are used in a series of reduction-oxidation (redox) reactions to produce sugars in a step-wise process; there is no direct reaction that converts several molecules of CO2 to a sugar. There are three phases to the light-independent reactions, collectively called the Calvin cycle: carboxylation, reduction reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration.

Contents

Though it is also called the "dark reaction," the Calvin cycle does not actually occur in the dark or during night time. This is because the process requires NADPH, which is short-lived and comes from light-dependent reactions. In the dark, plants instead release sucrose into the phloem from their starch reserves to provide energy for the plant. The Calvin cycle thus happens when light is available independent of the kind of photosynthesis (C3 carbon fixation, C4 carbon fixation, and crassulacean acid metabolism (CAM)); CAM plants store malic acid in their vacuoles every night and release it by day to make this process work. [2]

Coupling to other metabolic pathways

The reactions of the Calvin cycle are closely coupled to the thylakoid electron transport chain, as the energy required to reduce the carbon dioxide is provided by NADPH produced during the light dependent reactions. The process of photorespiration, also known as C2 cycle, is also coupled to the Calvin cycle, as it results from an alternative reaction of the RuBisCO enzyme, and its final byproduct is another glyceraldehyde-3-P molecule.

Calvin cycle

Overview of the Calvin cycle and carbon fixation Calvin-cycle4.svg
Overview of the Calvin cycle and carbon fixation

The Calvin cycle, Calvin–Benson–Bassham (CBB) cycle, reductive pentose phosphate cycle (RPP cycle) or C3 cycle is a series of biochemical redox reactions that take place in the stroma of chloroplast in photosynthetic organisms. The cycle was discovered in 1950 by Melvin Calvin, James Bassham, and Andrew Benson at the University of California, Berkeley [3] by using the radioactive isotope carbon-14.[ citation needed ]

Photosynthesis occurs in two stages in a cell. In the first stage, light-dependent reactions capture the energy of light and use it to make the energy-storage molecule ATP and the moderate-energy hydrogen carrier NADPH. The Calvin cycle uses these compounds to convert carbon dioxide and water into organic compounds [4] that can be used by the organism (and by animals that feed on it). This set of reactions is also called carbon fixation. The key enzyme of the cycle is called RuBisCO. In the following biochemical equations, the chemical species (phosphates and carboxylic acids) exist in equilibria among their various ionized states as governed by the pH.[ citation needed ]

The enzymes in the Calvin cycle are functionally equivalent to most enzymes used in other metabolic pathways such as gluconeogenesis and the pentose phosphate pathway, but the enzymes in the Calvin cycle are found in the chloroplast stroma instead of the cell cytosol, separating the reactions. They are activated in the light (which is why the name "dark reaction" is misleading), and also by products of the light-dependent reaction. These regulatory functions prevent the Calvin cycle from being respired to carbon dioxide. Energy (in the form of ATP) would be wasted in carrying out these reactions when they have no net productivity.[ citation needed ]

The sum of reactions in the Calvin cycle is the following:[ citation needed ]

3 CO
2 + 6 NADPH + 9 ATP + 5 H
2O → glyceraldehyde-3-phosphate (G3P) + 6 NADP+ + 9 ADP + 8 Pi  (Pi = inorganic phosphate)

Hexose (six-carbon) sugars are not products of the Calvin cycle. Although many texts list a product of photosynthesis as C
6H
12O
6, this is mainly for convenience to match the equation of aerobic respiration, where six-carbon sugars are oxidized in mitochondria. The carbohydrate products of the Calvin cycle are three-carbon sugar phosphate molecules, or "triose phosphates", namely, glyceraldehyde-3-phosphate (G3P).[ citation needed ]

Steps

In the first stage of the Calvin cycle, a CO2 molecule is incorporated into one of two three-carbon molecules (glyceraldehyde 3-phosphate or G3P), where it uses up two molecules of ATP and two molecules of NADPH, which had been produced in the light-dependent stage. The three steps involved are:[ citation needed ]

Calvin cycle step 1 (black circles represent carbon atoms) Calvin cycle step 1.svg
Calvin cycle step 1 (black circles represent carbon atoms)
Calvin cycle steps 2 and 3 combined Calvin cycle step 2 (doubled).svg
Calvin cycle steps 2 and 3 combined
  1. The enzyme RuBisCO catalyses the carboxylation of ribulose-1,5-bisphosphate, RuBP, a 5-carbon compound, by carbon dioxide (a total of 6 carbons) in a two-step reaction. [5] The product of the first step is enediol-enzyme complex that can capture CO
    2     or O
    2    . Thus, enediol-enzyme complex is the real carboxylase/oxygenase. The CO
    2     that is captured by enediol in second step produces an unstable six-carbon compound called 2-carboxy 3-keto 1,5-biphosphoribotol (CKABP [6] ) (or 3-keto-2-carboxyarabinitol 1,5-bisphosphate) that immediately splits into 2 molecules of 3-phosphoglycerate (also written as 3-phosphoglyceric acid, PGA, 3PGA, or 3-PGA), a 3-carbon compound. [7]
  2. The enzyme phosphoglycerate kinase catalyses the phosphorylation of 3-PGA by ATP (which was produced in the light-dependent stage). 1,3-Bisphosphoglycerate (glycerate-1,3-bisphosphate) and ADP are the products. (However, note that two 3-PGAs are produced for every CO
    2     that enters the cycle, so this step utilizes two ATP per CO
    2     fixed.)[ citation needed ]
  3. 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 CO
    2     fixed.[ citation needed ]
Regeneration stage of the Calvin cycle Calvin cycle step 3.svg
Regeneration stage of the Calvin cycle

The next stage in the Calvin cycle is to regenerate RuBP. Five G3P molecules produce three RuBP molecules, using up three molecules of ATP. Since each CO2 molecule produces two G3P molecules, three CO2 molecules produce six G3P molecules, of which five are used to regenerate RuBP, leaving a net gain of one G3P molecule per three CO2 molecules (as would be expected from the number of carbon atoms involved).[ citation needed ]

The regeneration stage of Calvin's cycle. Substances and their parts are outlined in colors: green - carbon accepting aldoses, pink - ketoses-donors of three-carbon groups, yellow - parts of ketoses remaining after donation of two-carbon keto-groups highlighted in orange. Enzymes are also highlighted: aldolases in purple and transketolases in red. V2 (Faza regeneratsii tsikl Kal'vina).svg
The regeneration stage of Calvin's cycle. Substances and their parts are outlined in colors: green - carbon accepting aldoses, pink - ketoses-donors of three-carbon groups, yellow - parts of ketoses remaining after donation of two-carbon keto-groups highlighted in orange. Enzymes are also highlighted: aldolases in purple and transketolases in red.
Simplified C3 cycle with structural formulas Calvin cycle.svg
Simplified C3 cycle with structural formulas

The regeneration stage can be broken down into a series of steps.

  1. Triose phosphate isomerase converts all of the G3P reversibly into dihydroxyacetone phosphate (DHAP), also a 3-carbon molecule.[ citation needed ]
  2. Aldolase and fructose-1,6-bisphosphatase convert a G3P and a DHAP into fructose 6-phosphate (6C). A phosphate ion is lost into solution.[ citation needed ]
  3. Then fixation of another CO
    2     generates two more G3P.[ citation needed ]
  4. F6P has two carbons removed by transketolase, giving erythrose-4-phosphate (E4P). The two carbons on transketolase are added to a G3P, giving the ketose xylulose-5-phosphate (Xu5P).[ citation needed ]
  5. E4P and a DHAP (formed from one of the G3P from the second CO
    2     fixation) are converted into sedoheptulose-1,7-bisphosphate (7C) by aldolase enzyme.[ citation needed ]
  6. Sedoheptulose-1,7-bisphosphatase (one of only three enzymes of the Calvin cycle that are unique to plants) cleaves sedoheptulose-1,7-bisphosphate into sedoheptulose-7-phosphate, releasing an inorganic phosphate ion into solution.[ citation needed ]
  7. Fixation of a third CO
    2     generates two more G3P. The ketose S7P has two carbons removed by transketolase, giving ribose-5-phosphate (R5P), and the two carbons remaining on transketolase are transferred to one of the G3P, giving another Xu5P. This leaves one G3P as the product of fixation of 3 CO
    2    , with generation of three pentoses that can be converted to Ru5P.[ citation needed ]
  8. R5P is converted into ribulose-5-phosphate (Ru5P, RuP) by phosphopentose isomerase. Xu5P is converted into RuP by phosphopentose epimerase.[ citation needed ]
  9. Finally, phosphoribulokinase (another plant-unique enzyme of the pathway) phosphorylates RuP into RuBP, ribulose-1,5-bisphosphate, completing the Calvin cycle. This requires the input of one ATP.[ citation needed ]

Thus, of six G3P produced, five are used to make three RuBP (5C) molecules (totaling 15 carbons), with only one G3P available for subsequent conversion to hexose. This requires nine ATP molecules and six NADPH molecules per three CO
2 molecules. The equation of the overall Calvin cycle is shown diagrammatically below.[ citation needed ]

The overall equation of the Calvin cycle (black circles represent carbon atoms) Calvin cycle overall.svg
The overall equation of the Calvin cycle (black circles represent carbon atoms)

RuBisCO also reacts competitively with O
2 instead of CO
2 in photorespiration. The rate of photorespiration is higher at high temperatures. Photorespiration turns RuBP into 3-PGA and 2-phosphoglycolate, a 2-carbon molecule that can be converted via glycolate and glyoxalate to glycine. Via the glycine cleavage system and tetrahydrofolate, two glycines are converted into serine plus CO
2. Serine can be converted back to 3-phosphoglycerate. Thus, only 3 of 4 carbons from two phosphoglycolates can be converted back to 3-PGA. It can be seen that photorespiration has very negative consequences for the plant, because, rather than fixing CO
2, this process leads to loss of CO
2. C4 carbon fixation evolved to circumvent photorespiration, but can occur only in certain plants native to very warm or tropical climates—corn, for example. Furthermore, RuBisCOs catalyzing the light-independent reactions of photosynthesis generally exhibit an improved specificity for CO2 relative to O2, in order to minimize the oxygenation reaction. This improved specificity evolved after RuBisCO incorporated a new protein subunit. [8]

Products

The immediate products of one turn of the Calvin cycle are 2 glyceraldehyde-3-phosphate (G3P) molecules, 3 ADP, and 2 NADP+. (ADP and NADP+ are not really "products". They are regenerated and later used again in the light-dependent reactions). Each G3P molecule is composed of 3 carbons. For the Calvin cycle to continue, RuBP (ribulose 1,5-bisphosphate) must be regenerated. So, 5 out of 6 carbons from the 2 G3P molecules are used for this purpose. Therefore, there is only 1 net carbon produced to play with for each turn. To create 1 surplus G3P requires 3 carbons, and therefore 3 turns of the Calvin cycle. To make one glucose molecule (which can be created from 2 G3P molecules) would require 6 turns of the Calvin cycle. Surplus G3P can also be used to form other carbohydrates such as starch, sucrose, and cellulose, depending on what the plant needs. [9]

Light-dependent regulation

These reactions do not occur in the dark or at night. There is a light-dependent regulation of the cycle enzymes, as the third step requires NADPH. [10]

There are two regulation systems at work when the cycle must be turned on or off: the thioredoxin/ferredoxin activation system, which activates some of the cycle enzymes; and the RuBisCo enzyme activation, active in the Calvin cycle, which involves its own activase. [11]

The thioredoxin/ferredoxin system activates the enzymes glyceraldehyde-3-P dehydrogenase, glyceraldehyde-3-P phosphatase, fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase, and ribulose-5-phosphatase kinase, which are key points of the process. This happens when light is available, as the ferredoxin protein is reduced in the photosystem I complex of the thylakoid electron chain when electrons are circulating through it. [12] Ferredoxin then binds to and reduces the thioredoxin protein, which activates the cycle enzymes by severing a cystine bond found in all these enzymes. This is a dynamic process as the same bond is formed again by other proteins that deactivate the enzymes. The implications of this process are that the enzymes remain mostly activated by day and are deactivated in the dark when there is no more reduced ferredoxin available.[ citation needed ]

The enzyme RuBisCo has its own, more complex activation process. It requires that a specific lysine amino acid be carbamylated to activate the enzyme. This lysine binds to RuBP and leads to a non-functional state if left uncarbamylated. A specific activase enzyme, called RuBisCo activase, helps this carbamylation process by removing one proton from the lysine and making the binding of the carbon dioxide molecule possible. Even then the RuBisCo enzyme is not yet functional, as it needs a magnesium ion bound to the lysine to function. This magnesium ion is released from the thylakoid lumen when the inner pH drops due to the active pumping of protons from the electron flow. RuBisCo activase itself is activated by increased concentrations of ATP in the stroma caused by its phosphorylation. [13]

Related Research Articles

<span class="mw-page-title-main">Photosynthesis</span> Biological process to convert light into chemical energy

Photosynthesis is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their activities. Photosynthetic organisms use intracellular organic compounds to store the chemical energy they produce in photosynthesis within organic compounds like sugars, glycogen, cellulose and starches. Photosynthesis is usually used to refer to oxygenic photosynthesis, a process that produces oxygen. To use this stored chemical energy, the organisms' cells metabolize the organic compounds through another process called cellular respiration. Photosynthesis plays a critical role in producing and maintaining the oxygen content of the Earth's atmosphere, and it supplies most of the biological energy necessary for complex life on Earth.

<span class="mw-page-title-main">RuBisCO</span> Key enzyme of photosynthesis involved in carbon fixation

Ribulose-1,5-bisphosphate carboxylase/oxygenase, commonly known by the abbreviations RuBisCo, rubisco, RuBPCase, or RuBPco, is an enzyme involved in light-independent part of photosynthesis, including the carbon fixation by which atmospheric carbon dioxide is converted by plants and other photosynthetic organisms to energy-rich molecules such as glucose. It emerged approximately four billion years ago in primordial metabolism prior to the presence of oxygen on Earth. It is probably the most abundant enzyme on Earth. In chemical terms, it catalyzes the carboxylation of ribulose-1,5-bisphosphate.

C<sub>4</sub> carbon fixation Photosynthetic process in some plants

C4 carbon fixation or the Hatch–Slack pathway is one of three known photosynthetic processes of carbon fixation in plants. It owes the names to the 1960s discovery by Marshall Davidson Hatch and Charles Roger Slack.

<span class="mw-page-title-main">Photorespiration</span> Process in plant metabolism

Photorespiration (also known as the oxidative photosynthetic carbon cycle or C2 cycle) refers to a process in plant metabolism where the enzyme RuBisCO oxygenates RuBP, wasting some of the energy produced by photosynthesis. 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. This process lowers the efficiency of photosynthesis, potentially lowering photosynthetic output by 25% in C3 plants. Photorespiration involves a complex network of enzyme reactions that exchange metabolites between chloroplasts, leaf peroxisomes and mitochondria.

<span class="mw-page-title-main">Ribulose 1,5-bisphosphate</span> Chemical compound

Ribulose 1,5-bisphosphate (RuBP) is an organic substance that is involved in photosynthesis, notably as the principal CO2 acceptor in plants. It is a colourless anion, a double phosphate ester of the ketopentose called ribulose. Salts of RuBP can be isolated, but its crucial biological function happens in solution. RuBP occurs not only in plants but in all domains of life, including Archaea, Bacteria, and Eukarya.

C<sub>3</sub> carbon fixation Series of interconnected biochemical reactions

C3 carbon fixation is the most common of three metabolic pathways for carbon fixation in photosynthesis, the other two being C4 and CAM. This process converts carbon dioxide and ribulose bisphosphate (RuBP, a 5-carbon sugar) into two molecules of 3-phosphoglycerate through the following reaction:

<span class="mw-page-title-main">Biological carbon fixation</span> Series of interconnected biochemical reactions

Biological carbon fixation or сarbon assimilation is the process by which inorganic carbon is converted to organic compounds by living organisms. The compounds are then used to store energy and as structure for other biomolecules. Carbon is primarily fixed through photosynthesis, but some organisms use a process called chemosynthesis in the absence of sunlight.

<span class="mw-page-title-main">Glyceraldehyde 3-phosphate</span> Chemical compound

Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GA3P, GADP, GAP, TP, GALP or PGAL, is a metabolite that occurs as an intermediate in several central pathways of all organisms. With the chemical formula H(O)CCH(OH)CH2OPO32-, this anion is a monophosphate ester of glyceraldehyde.

Methylotrophs are a diverse group of microorganisms that can use reduced one-carbon compounds, such as methanol or methane, as the carbon source for their growth; and multi-carbon compounds that contain no carbon-carbon bonds, such as dimethyl ether and dimethylamine. This group of microorganisms also includes those capable of assimilating reduced one-carbon compounds by way of carbon dioxide using the ribulose bisphosphate pathway. These organisms should not be confused with methanogens which on the contrary produce methane as a by-product from various one-carbon compounds such as carbon dioxide. Some methylotrophs can degrade the greenhouse gas methane, and in this case they are called methanotrophs. The abundance, purity, and low price of methanol compared to commonly used sugars make methylotrophs competent organisms for production of amino acids, vitamins, recombinant proteins, single-cell proteins, co-enzymes and cytochromes.

<span class="mw-page-title-main">3-Phosphoglyceric acid</span> Chemical compound

3-Phosphoglyceric acid (3PG, 3-PGA, or PGA) is the conjugate acid of 3-phosphoglycerate or glycerate 3-phosphate (GP or G3P). This glycerate is a biochemically significant metabolic intermediate in both glycolysis and the Calvin-Benson cycle. The anion is often termed as PGA when referring to the Calvin-Benson cycle. In the Calvin-Benson cycle, 3-phosphoglycerate is typically the product of the spontaneous scission of an unstable 6-carbon intermediate formed upon CO2 fixation. Thus, two equivalents of 3-phosphoglycerate are produced for each molecule of CO2 that is fixed. In glycolysis, 3-phosphoglycerate is an intermediate following the dephosphorylation (reduction) of 1,3-bisphosphoglycerate.

<span class="mw-page-title-main">1,3-Bisphosphoglyceric acid</span> Chemical compound

1,3-Bisphosphoglyceric acid (1,3-Bisphosphoglycerate or 1,3BPG) is a 3-carbon organic molecule present in most, if not all, living organisms. It primarily exists as a metabolic intermediate in both glycolysis during respiration and the Calvin cycle during photosynthesis. 1,3BPG is a transitional stage between glycerate 3-phosphate and glyceraldehyde 3-phosphate during the fixation/reduction of CO2. 1,3BPG is also a precursor to 2,3-bisphosphoglycerate which in turn is a reaction intermediate in the glycolytic pathway.

<span class="mw-page-title-main">Phosphoenolpyruvate carboxylase</span> Class of enzymes

Phosphoenolpyruvate carboxylase (also known as PEP carboxylase, PEPCase, or PEPC; EC 4.1.1.31, PDB ID: 3ZGE) is an enzyme in the family of carboxy-lyases found in plants and some bacteria that catalyzes the addition of bicarbonate (HCO3−) to phosphoenolpyruvate (PEP) to form the four-carbon compound oxaloacetate and inorganic phosphate:

<span class="mw-page-title-main">Fructose-bisphosphate aldolase</span>

Fructose-bisphosphate aldolase, often just aldolase, is an enzyme catalyzing a reversible reaction that splits the aldol, fructose 1,6-bisphosphate, into the triose phosphates dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (G3P). Aldolase can also produce DHAP from other (3S,4R)-ketose 1-phosphates such as fructose 1-phosphate and sedoheptulose 1,7-bisphosphate. Gluconeogenesis and the Calvin cycle, which are anabolic pathways, use the reverse reaction. Glycolysis, a catabolic pathway, uses the forward reaction. Aldolase is divided into two classes by mechanism.

<span class="mw-page-title-main">Phosphoribulokinase</span>

Phosphoribulokinase (PRK) (EC 2.7.1.19) is an essential photosynthetic enzyme that catalyzes the ATP-dependent phosphorylation of ribulose 5-phosphate (RuP) into ribulose 1,5-bisphosphate (RuBP), both intermediates in the Calvin Cycle. Its main function is to regenerate RuBP, which is the initial substrate and CO2-acceptor molecule of the Calvin Cycle. PRK belongs to the family of transferase enzymes, specifically those transferring phosphorus-containing groups (phosphotransferases) to an alcohol group acceptor. Along with ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCo), phosphoribulokinase is unique to the Calvin Cycle. Therefore, PRK activity often determines the metabolic rate in organisms for which carbon fixation is key to survival. Much initial work on PRK was done with spinach leaf extracts in the 1950s; subsequent studies of PRK in other photosynthetic prokaryotic and eukaryotic organisms have followed. The possibility that PRK might exist was first recognized by Weissbach et al. in 1954; for example, the group noted that carbon dioxide fixation in crude spinach extracts was enhanced by the addition of ATP. The first purification of PRK was conducted by Hurwitz and colleagues in 1956.

ATP + Mg2+ - D-ribulose 5-phosphate  ADP + D-ribulose 1,5-bisphosphate

Bisphosphate may refer to:

<span class="mw-page-title-main">Stroma (fluid)</span> In plants, the colorless fluid surrounding the grana within the chloroplast

Stroma, in botany, refers to the colorless fluid surrounding the grana within the chloroplast.

2-Carboxy-<small>D</small>-arabitinol 1-phosphate Chemical compound

2-Carboxy-D-arabitinol 1-phosphate is a molecule produced in plants that inhibits RuBisCO, a key enzyme in the Calvin cycle and carbon fixation. In dark conditions, this molecule binds to RuBisCO, preventing it from participating in chemical reactions. As the amount of light present increases, CA1P levels decrease, freeing RuBisCO's reactive ends, allowing more of the molecules to participate in chemical reactions. It can be broken down by the enzyme 2-carboxy-D-arabinitol-1-phosphatase into 2-carboxy-D-arabinitol.

<span class="mw-page-title-main">Fractionation of carbon isotopes in oxygenic photosynthesis</span>

Photosynthesis converts carbon dioxide to carbohydrates via several metabolic pathways that provide energy to an organism and preferentially react with certain stable isotopes of carbon. The selective enrichment of one stable isotope over another creates distinct isotopic fractionations that can be measured and correlated among oxygenic phototrophs. The degree of carbon isotope fractionation is influenced by several factors, including the metabolism, anatomy, growth rate, and environmental conditions of the organism. Understanding these variations in carbon fractionation across species is useful for biogeochemical studies, including the reconstruction of paleoecology, plant evolution, and the characterization of food chains.

<span class="mw-page-title-main">Kinetic isotope effects of RuBisCO</span>

The kinetic isotope effect (KIE) of ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) is the isotopic fractionation associated solely with the step in the Calvin-Benson cycle where a molecule of carbon dioxide is attached to the 5-carbon sugar ribulose-1,5-bisphosphate (RuBP) to produce two 3-carbon sugars called 3-phosphoglycerate. This chemical reaction is catalyzed by the enzyme RuBisCO, and this enzyme-catalyzed reaction creates the primary kinetic isotope effect of photosynthesis. It is also largely responsible for the isotopic compositions of photosynthetic organisms and the heterotrophs that eat them. Understanding the intrinsic KIE of RuBisCO is of interest to earth scientists, botanists, and ecologists because this isotopic biosignature can be used to reconstruct the evolution of photosynthesis and the rise of oxygen in the geologic record, reconstruct past evolutionary relationships and environmental conditions, and infer plant relationships and productivity in modern environments.

<span class="mw-page-title-main">2-Phosphoglycolate</span> Chemical compound

2-Phosphoglycolate (chemical formula C2H2O6P3-; also known as phosphoglycolate, 2-PG, or PG) is a natural metabolic product of the oxygenase reaction mediated by the enzyme ribulose 1,5-bisphosphate carboxylase (RuBisCo).

References

  1. ↑ Silverstein, Alvin (2008). Photosynthesis. Twenty-First Century Books. p. 21. ISBN   9780822567981.
  2. ↑ Cushman, John C. (2001). "A plastic photosynthetic adaptation to arid environments". Plant Physiology . 127 (4): 1439–1448. doi:10.1104/pp.010818. PMC   1540176 . PMID   11743087.
  3. ↑ Bassham J, Benson A, Calvin M (1950). "The path of carbon in photosynthesis" (PDF). J Biol Chem. 185 (2): 781–7. doi:10.2172/910351. PMID   14774424. Archived from the original (PDF) on 2009-02-19. Retrieved 2013-07-03.
  4. ↑ Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN   0-13-250882-6.
  5. ↑ Farazdaghi H (2009). "Modeling the Kinetics of Activation and Reaction of Rubisco from Gas Exchange". Photosynthesis in silico. Advances in Photosynthesis and Respiration. Vol. 29. pp. 275–294. doi:10.1007/978-1-4020-9237-4_12. ISBN   978-1-4020-9236-7.
  6. ↑ Lorimer, G.H.; Andrews, T.J.; Pierce, J.; Schloss, J.V. (1986). "2´-carboxy-3-keto-D-arabinitol 1,5-bisphosphate, the six-carbon intermediate of the ribulose bisphosphate carboxylase reaction". Phil. Trans. R. Soc. Lond. B. 313 (1162): 397–407. Bibcode:1986RSPTB.313..397L. doi:10.1098/rstb.1986.0046.
  7. ↑ Campbell, and Reece Biology: 8th Edition, page 198. Benjamin Cummings, December 7, 2007.
  8. ↑ Schulz, L; Guo, Z; Zarzycki, J; Steinchen, W; Schuller, JM; Heimerl, T; Prinz, S; Mueller-Cajar, O; Erb, TJ; Hochberg, GKA (14 October 2022). "Evolution of increased complexity and specificity at the dawn of form I Rubiscos". Science. 378 (6616): 155–160. Bibcode:2022Sci...378..155S. doi:10.1126/science.abq1416. PMID   36227987. S2CID   252897276.
  9. ↑ Russell, Wolfe et al.Biology: Exploring the Diversity of Life.Toronto:Nelson College Indigenous,1st ed, Vol. 1, 2010, pg 151
  10. ↑ Schreier, Tina; Hibberd, Julian (1 March 2019). "Variations in the Calvin–Benson cycle: selection pressures and optimization?". Journal of Experimental Botany. 70 (6) (published 27 March 2019): 1697–1701. doi:10.1093/jxb/erz078. PMC   6436154 . PMID   30916343 – via Oxford Academic.
  11. ↑ Konwarh, Rocktotpal; Abda, Ebrahim M.; Haregu, Simatsidk; Singh, Anand Pratap (2022-01-01), Khan, Raju; Murali, S.; Gogoi, Satyabrat (eds.), "Chapter 7 - Exemplary evidence of bio-nano crosstalk between carbon dots and plant systems", Carbon Dots in Agricultural Systems, Academic Press, pp. 155–173, ISBN   978-0-323-90260-1 , retrieved 2023-04-22
  12. ↑ Besse, I; Buchanan, B (1997). "Thioredoxin-linked animal and plant processes: the new generation". Bot. Bull. Acad. Sin. 38: 1–11.
  13. ↑ Ruuska, Sari A.; Andrews, T. John; Badger, Murray R.; Price, G. Dean; von Caemmerer, Susanne (2000-02-01). "The Role of Chloroplast Electron Transport and Metabolites in Modulating Rubisco Activity in Tobacco. Insights from Transgenic Plants with Reduced Amounts of Cytochrome b/f Complex or Glyceraldehyde 3-Phosphate Dehydrogenase". Plant Physiology. 122 (2): 491–504. doi:10.1104/pp.122.2.491. ISSN   1532-2548. PMC   58886 . PMID   10677442.

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