Template:Short description Template:Infobox enzyme
Ribulose-1,5-bisphosphate carboxylase/oxygenase, commonly known by the abbreviations RuBisCo, rubisco,<ref name="Sharkey_2018">Template:Cite journal</ref> RuBPCase,<ref>Template:Cite journal</ref> or RuBPco,<ref>Template:Cite journal</ref> is an enzyme (Template:EnzExplorer) involved in the light-independent (or "dark") 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.<ref>Back to the future of photosynthesis: Resurrecting billon-year-old enzymes reveals how photosynthesis adapted to the rise of oxygen., News from the Max Planck Society, October 13, 2022</ref> It is probably the most abundant enzyme on Earth. In chemical terms, it catalyzes the carboxylation of ribulose-1,5-bisphosphate (also known as RuBP).<ref>Template:Cite book</ref><ref name = "Dhingra_2004">Template:Cite journal</ref><ref name="Feller_2008">Template:Cite journal</ref>
Alternative carbon fixation pathwaysEdit
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. Phosphoenolpyruvate carboxylase, unlike RuBisCO, only temporarily fixes carbon. Reflecting its importance, RuBisCO is the most abundant protein in leaves, accounting for 50% of soluble leaf protein in [[C3 carbon fixation|Template:C3 plants]] (20–30% of total leaf nitrogen) and 30% of soluble leaf protein in [[C4 carbon fixation|Template:C4 plants]] (5–9% of total leaf nitrogen).<ref name="Feller_2008"/> Given its important role in the biosphere, the genetic engineering of RuBisCO in crops is of continuing interest (see below).
StructureEdit
In plants, algae, cyanobacteria, and phototrophic and chemoautotrophic Pseudomonadota (formerly proteobacteria), the enzyme usually consists of two types of protein subunit, called the large chain (L, about 55,000 Da) and the small chain (S, about 13,000 Da). The large-chain gene (rbcL) is encoded by the chloroplast DNA in plants.<ref name="pmid29594130">Template:Cite journal</ref> There are typically several related small-chain genes in the nucleus of plant cells, and the small chains are imported to the stromal compartment of chloroplasts from the cytosol by crossing the outer chloroplast membrane.<ref name = "Dhingra_2004" /><ref name="pmid11401297">Arabidopsis thaliana has four RuBisCO small chain genes.
Template:Cite journal</ref> The enzymatically active substrate (ribulose 1,5-bisphosphate) binding sites are located in the large chains that form dimers in which amino acids from each large chain contribute to the binding sites. A total of eight large chains (= four dimers) and eight small chains assemble into a larger complex of about 540,000 Da.<ref>Template:Cite book
</ref> In some Pseudomonadota and dinoflagellates, enzymes consisting of only large subunits have been found.Template:Efn
Magnesium ions (Template:Chem2) are needed for enzymatic activity. Correct positioning of Template:Chem2 in the active site of the enzyme involves addition of an "activating" carbon dioxide molecule ([[Carbon dioxide|Template:CO2]]) to a lysine in the active site (forming a carbamate).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }} Figure 16-48 shows a structural model of the active site, including the involvement of magnesium.</ref> Template:Chem2 operates by driving deprotonation of the Lys210 residue, causing the Lys residue to rotate by 120 degrees to the trans conformer, decreasing the distance between the nitrogen of Lys and the carbon of Template:CO2. The close proximity allows for the formation of a covalent bond, resulting in the carbamate.<ref name="Stec_2012">Template:Cite journal</ref> Template:Chem2 is first enabled to bind to the active site by the rotation of His335 to an alternate conformation. Template:Chem2 is then coordinated by the His residues of the active site (His300, His302, His335), and is partially neutralized by the coordination of three water molecules and their conversion to −OH.<ref name="Stec_2012" /> This coordination results in an unstable complex, but produces a favorable environment for the binding of Template:Chem2. Formation of the carbamate is favored by an alkaline pH. The pH and the concentration of magnesium ions in the fluid compartment (in plants, the stroma of the chloroplast) increases in the light. The role of changing pH and magnesium ion levels in the regulation of RuBisCO enzyme activity is discussed below. Once the carbamate is formed, His335 finalizes the activation by returning to its initial position through thermal fluctuation.<ref name="Stec_2012" />
| Template:Infobox protein family | Template:Infobox protein family | Template:Infobox protein family |
Enzymatic activityEdit
RuBisCO is one of many enzymes in the Calvin cycle. When Rubisco facilitates the attack of Template:CO2 at the C2 carbon of RuBP and subsequent bond cleavage between the C3 and C2 carbon, 2 molecules of glycerate-3-phosphate are formed. The conversion involves these steps: enolisation, carboxylation, hydration, C-C bond cleavage, and protonation.<ref name="Andersson_2008">Template:Cite journal</ref><ref name = "Erb_2018">Template:Cite journal</ref><ref>Template:Cite journal</ref>
SubstratesEdit
Substrates for RuBisCO are ribulose-1,5-bisphosphate and carbon dioxide (distinct from the "activating" carbon dioxide). RuBisCO also catalyses a reaction of ribulose-1,5-bisphosphate and molecular oxygen (O2) instead of carbon dioxide (Template:CO2).<ref name = "Goodsell_2000">Template:Cite journal</ref> Discriminating between the substrates Template:CO2 and O2 is attributed to the differing interactions of the substrate's quadrupole moments and a high electrostatic field gradient.<ref name="Stec_2012" /> This gradient is established by the dimer form of the minimally active RuBisCO, which with its two components provides a combination of oppositely charged domains required for the enzyme's interaction with O2 and Template:CO2. These conditions help explain the low turnover rate found in RuBisCO: In order to increase the strength of the electric field necessary for sufficient interaction with the substrates’ quadrupole moments, the C- and N- terminal segments of the enzyme must be closed off, allowing the active site to be isolated from the solvent and lowering the dielectric constant.<ref>Template:Cite journal</ref> This isolation has a significant entropic cost, and results in the poor turnover rate.
Binding RuBPEdit
Carbamylation of the ε-amino group of Lys210 is stabilized by coordination with the Template:Chem2.<ref>Template:Cite journal</ref> This reaction involves binding of the carboxylate termini of Asp203 and Glu204 to the Template:Chem2 ion. The substrate RuBP binds Template:Chem2 displacing two of the three aquo ligands.<ref name="Andersson_2008"/><ref name="genbase">Template:Cite journal</ref><ref name ="Andersson _1989">Template:Cite journal</ref>
EnolisationEdit
Enolisation of RuBP is the conversion of the keto tautomer of RuBP to an enediol(ate). Enolisation is initiated by deprotonation at C3. The enzyme base in this step has been debated,<ref name="genbase"/><ref name="Hartman_1994">Template:Cite journal</ref> but the steric constraints observed in crystal structures have made Lys210 the most likely candidate.<ref name="Andersson_2008"/> Specifically, the carbamate oxygen on Lys210 that is not coordinated with the Mg ion deprotonates the C3 carbon of RuBP to form a 2,3-enediolate.<ref name="genbase"/><ref name ="Andersson _1989"/>
CarboxylationEdit
Carboxylation of the 2,3-enediolate results in the intermediate 3-keto-2-carboxyarabinitol-1,5-bisphosphate and Lys334 is positioned to facilitate the addition of the Template:CO2 substrate as it replaces the third Template:Chem2-coordinated water molecule and add directly to the enediol. No Michaelis complex is formed in this process.<ref name="Andersson_2008"/><ref name="Hartman_1994"/> Hydration of this ketone results in an additional hydroxy group on C3, forming a gem-diol intermediate.<ref name="genbase"/><ref name="and1997">Template:Cite journal</ref> Carboxylation and hydration have been proposed as either a single concerted step<ref name="genbase"/> or as two sequential steps.<ref name="and1997"/> Concerted mechanism is supported by the proximity of the water molecule to C3 of RuBP in multiple crystal structures. Within the spinach structure, other residues are well placed to aid in the hydration step as they are within hydrogen bonding distance of the water molecule.<ref name="Andersson_2008"/>
C-C bond cleavageEdit
The gem-diol intermediate cleaves at the C2-C3 bond to form one molecule of glycerate-3-phosphate and a negatively charged carboxylate.<ref name="Andersson_2008"/> Stereo specific protonation of C2 of this carbanion results in another molecule of glycerate-3-phosphate. This step is thought to be facilitated by Lys175 or potentially the carbamylated Lys210.<ref name="Andersson_2008"/>
ProductsEdit
When carbon dioxide is the substrate, the product of the carboxylase reaction is an unstable six-carbon phosphorylated intermediate known as 3-keto-2-carboxyarabinitol-1,5-bisphosphate, which decays rapidly into two molecules of glycerate-3-phosphate. This product, also known as 3-phosphoglycerate, can be used to produce larger molecules such as glucose.
When molecular oxygen is the substrate, the products of the oxygenase reaction are phosphoglycolate and 3-phosphoglycerate. Phosphoglycolate is recycled through a sequence of reactions called photorespiration, which involves enzymes and cytochromes located in the mitochondria and peroxisomes (this is a case of metabolite repair). In this process, two molecules of phosphoglycolate are converted to one molecule of carbon dioxide and one molecule of 3-phosphoglycerate, which can reenter the Calvin cycle. Some of the phosphoglycolate entering this pathway can be retained by plants to produce other molecules such as glycine. At ambient levels of carbon dioxide and oxygen, the ratio of the reactions is about 4 to 1, which results in a net carbon dioxide fixation of only 3.5. Thus, the inability of the enzyme to prevent the reaction with oxygen greatly reduces the photosynthetic capacity of many plants. Some plants, many algae, and photosynthetic bacteria have overcome this limitation by devising means to increase the concentration of carbon dioxide around the enzyme, including [[C4 carbon fixation|Template:C4 carbon fixation]], crassulacean acid metabolism, and the use of pyrenoid.
Rubisco side activities can lead to useless or inhibitory by-products. Important inhibitory by-products include xylulose 1,5-bisphosphate and glycero-2,3-pentodiulose 1,5-bisphosphate, both caused by "misfires" halfway in the enolisation-carboxylation reaction. In higher plants, this process causes RuBisCO self-inhibition, which can be triggered by saturating Template:CO2 and RuBP concentrations and solved by Rubisco activase (see below).<ref>Template:Cite journal</ref>
Rate of enzymatic activityEdit
Some enzymes can carry out thousands of chemical reactions each second. However, RuBisCO is slow, fixing only 3–10 carbon dioxide molecules each second per molecule of enzyme.<ref>Template:Cite journal</ref> The reaction catalyzed by RuBisCO is, thus, the primary rate-limiting factor of the Calvin cycle during the day. Nevertheless, under most conditions, and when light is not otherwise limiting photosynthesis, the speed of RuBisCO responds positively to increasing carbon dioxide concentration.
RuBisCO is usually only active during the day, as ribulose 1,5-bisphosphate is not regenerated in the dark. This is due to the regulation of several other enzymes in the Calvin cycle. In addition, the activity of RuBisCO is coordinated with that of the other enzymes of the Calvin cycle in several other ways:
By ionsEdit
Upon illumination of the chloroplasts, the pH of the stroma rises from 7.0 to 8.0 because of the proton (hydrogen ion, Template:Chem2) gradient created across the thylakoid membrane. The movement of protons into thylakoids is driven by light and is fundamental to ATP synthesis in chloroplasts (Further reading: Photosynthetic reaction centre; Light-dependent reactions). To balance ion potential across the membrane, magnesium ions (Template:Chem2) move out of the thylakoids in response, increasing the concentration of magnesium in the stroma of the chloroplasts. RuBisCO has a high optimal pH (can be >9.0, depending on the magnesium ion concentration) and, thus, becomes "activated" by the introduction of carbon dioxide and magnesium to the active sites as described above.
By RuBisCO activaseEdit
In plants and some algae, another enzyme, RuBisCO activase (Rca, Template:GO, Template:UniProt), is required to allow the rapid formation of the critical carbamate in the active site of RuBisCO.<ref name="pmid16245090">Template:Cite journal</ref><ref name="pmid15236471">Template:Cite journal</ref> This is required because ribulose 1,5-bisphosphate (RuBP) binds more strongly to the active sites of RuBisCO when excess carbamate is present, preventing processes from moving forward. In the light, RuBisCO activase promotes the release of the inhibitory (or — in some views — storage) RuBP from the catalytic sites of RuBisCO. Activase is also required in some plants (e.g., tobacco and many beans) because, in darkness, RuBisCO is inhibited (or protected from hydrolysis) by a competitive inhibitor synthesized by these plants, a substrate analog 2-carboxy-D-arabitinol 1-phosphate (CA1P).<ref name="pmid7818481">Template:Cite journal</ref> CA1P binds tightly to the active site of carbamylated RuBisCO and inhibits catalytic activity to an even greater extent. CA1P has also been shown to keep RuBisCO in a conformation that is protected from proteolysis.<ref>Template:Cite journal</ref> In the light, RuBisCO activase also promotes the release of CA1P from the catalytic sites. After the CA1P is released from RuBisCO, it is rapidly converted to a non-inhibitory form by a light-activated CA1P-phosphatase. Even without these strong inhibitors, once every several hundred reactions, the normal reactions with carbon dioxide or oxygen are not completed; other inhibitory substrate analogs are still formed in the active site. Once again, RuBisCO activase can promote the release of these analogs from the catalytic sites and maintain the enzyme in a catalytically active form. However, at high temperatures, RuBisCO activase aggregates and can no longer activate RuBisCO. This contributes to the decreased carboxylating capacity observed during heat stress.<ref name="pmid11706186">Template:Cite journal</ref><ref name="pmid11069297">Template:Cite journal</ref>
By activaseEdit
The removal of the inhibitory RuBP, CA1P, and the other inhibitory substrate analogs by activase requires the consumption of ATP. This reaction is inhibited by the presence of ADP, and, thus, activase activity depends on the ratio of these compounds in the chloroplast stroma. Furthermore, in most plants, the sensitivity of activase to the ratio of ATP/ADP is modified by the stromal reduction/oxidation (redox) state through another small regulatory protein, thioredoxin. In this manner, the activity of activase and the activation state of RuBisCO can be modulated in response to light intensity and, thus, the rate of formation of the ribulose 1,5-bisphosphate substrate.<ref>Template:Cite journal</ref>
By phosphateEdit
In cyanobacteria, inorganic phosphate (Pi) also participates in the co-ordinated regulation of photosynthesis: Pi binds to the RuBisCO active site and to another site on the large chain where it can influence transitions between activated and less active conformations of the enzyme. In this way, activation of bacterial RuBisCO might be particularly sensitive to Pi levels, which might cause it to act in a similar way to how RuBisCO activase functions in higher plants.<ref>Template:Cite journal</ref>
By carbon dioxideEdit
Since carbon dioxide and oxygen compete at the active site of RuBisCO, carbon fixation by RuBisCO can be enhanced by increasing the carbon dioxide level in the compartment containing RuBisCO (chloroplast stroma). Several times during the evolution of plants, mechanisms have evolved for increasing the level of carbon dioxide in the stroma (see [[C4 carbon fixation|Template:C4 carbon fixation]]). The use of oxygen as a substrate appears to be a puzzling process, since it seems to throw away captured energy. However, it may be a mechanism for preventing carbohydrate overload during periods of high light flux. This weakness in the enzyme is the cause of photorespiration, such that healthy leaves in bright light may have zero net carbon fixation when the ratio of O2 to Template:CO2 available to RuBisCO shifts too far towards oxygen. This phenomenon is primarily temperature-dependent: high temperatures can decrease the concentration of Template:CO2 dissolved in the moisture of leaf tissues. This phenomenon is also related to water stress: since plant leaves are evaporatively cooled, limited water causes high leaf temperatures. [[C4 plants|Template:C4 plants]] use the enzyme PEP carboxylase initially, which has a higher affinity for Template:CO2. The process first makes a 4-carbon intermediate compound, hence the name Template:C4 plants, which is shuttled into a site of [[C3 plants|Template:C3 photosynthesis]] then decarboxylated, releasing Template:CO2 to boost the concentration of Template:CO2.
Crassulacean acid metabolism (CAM) plants keep their stomata closed during the day, which conserves water but prevents the light-independent reactions (a.k.a. the Calvin Cycle) from taking place, since these reactions require Template:CO2 to pass by gas exchange through these openings. Evaporation through the upper side of a leaf is prevented by a layer of wax.
Genetic engineeringEdit
Since RuBisCO is often rate-limiting for photosynthesis in plants, it may be possible to improve photosynthetic efficiency by modifying RuBisCO genes in plants to increase catalytic activity and/or decrease oxygenation rates.<ref>Template:Cite journal</ref><ref name="John_Timmer_2017">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="John_Timmer_2019">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="South_2019">Template:Cite journal</ref> This could improve [[Carbon sequestration|sequestration of Template:CO2]] and be a strategy to increase crop yields.<ref name="Furbank_2015">Template:Cite journal</ref> Approaches under investigation include transferring RuBisCO genes from one organism into another organism, engineering Rubisco activase from thermophilic cyanobacteria into temperature sensitive plants, increasing the level of expression of RuBisCO subunits, expressing RuBisCO small chains from the chloroplast DNA, and altering RuBisCO genes to increase specificity for carbon dioxide or otherwise increase the rate of carbon fixation.<ref name = "Parry_2003">Template:Cite journal</ref><ref>Template:Cite journal</ref>
Mutagenesis in plantsEdit
In general, site-directed mutagenesis of RuBisCO has been mostly unsuccessful,<ref name="Furbank_2015" /> though mutated forms of the protein have been achieved in tobacco plants with subunit C4 species,<ref>Template:Cite journal</ref> and a RuBisCO with more C4-like kinetic characteristics have been attained in rice via nuclear transformation.<ref>Template:Cite journal</ref> Robust and reliable engineering for yield of RuBisCO and other enzymes in the C3 cycle was shown to be possible,<ref>Template:Cite book</ref> and it was first achieved in 2019 through a synthetic biology approach.<ref name="South_2019" />
One avenue is to introduce RuBisCO variants with naturally high specificity values such as the ones from the red alga Galdieria partita into plants. This may improve the photosynthetic efficiency of crop plants, although possible negative impacts have yet to be studied.<ref>Template:Cite journal</ref> Advances in this area include the replacement of the tobacco enzyme with that of the purple photosynthetic bacterium Rhodospirillum rubrum.<ref>Template:Cite journal</ref> In 2014, two transplastomic tobacco lines with functional RuBisCO from the cyanobacterium Synechococcus elongatus PCC7942 (Se7942) were created by replacing the RuBisCO with the large and small subunit genes of the Se7942 enzyme, in combination with either the corresponding Se7942 assembly chaperone, RbcX, or an internal carboxysomal protein, CcmM35. Both mutants had increased Template:CO2 fixation rates when measured as carbon molecules per RuBisCO. However, the mutant plants grew more slowly than wild-type.<ref>Template:Cite journal</ref>
A recent theory explores the trade-off between the relative specificity (i.e., ability to favour Template:CO2 fixation over O2 incorporation, which leads to the energy-wasteful process of photorespiration) and the rate at which product is formed. The authors conclude that RuBisCO may actually have evolved to reach a point of 'near-perfection' in many plants (with widely varying substrate availabilities and environmental conditions), reaching a compromise between specificity and reaction rate.<ref name=Tcherkez06>Template:Cite journal</ref> It has been also suggested that the oxygenase reaction of RuBisCO prevents Template:CO2 depletion near its active sites and provides the maintenance of the chloroplast redox state.<ref>Template:Cite journal</ref>
Since photosynthesis is the single most effective natural regulator of carbon dioxide in the Earth's atmosphere,<ref>Template:Cite journal</ref> a biochemical model of RuBisCO reaction is used as the core module of climate change models. Thus, a correct model of this reaction is essential to the basic understanding of the relations and interactions of environmental models.
Expression in bacterial hostsEdit
There currently are very few effective methods for expressing functional plant Rubisco in bacterial hosts for genetic manipulation studies. This is largely due to Rubisco's requirement of complex cellular machinery for its biogenesis and metabolic maintenance including the nuclear-encoded RbcS subunits, which are typically imported into chloroplasts as unfolded proteins.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Furthermore, sufficient expression and interaction with Rubisco activase are major challenges as well.<ref name = "Parry_2003" /> One successful method for expression of Rubisco in E. coli involves the co-expression of multiple chloroplast chaperones, though this has only been shown for Arabidopsis thaliana Rubisco.<ref>Template:Cite journal</ref>
Depletion in proteomic studiesEdit
Due to its high abundance in plants (generally 40% of the total protein content), RuBisCO often impedes analysis of important signaling proteins such as transcription factors, kinases, and regulatory proteins found in lower abundance (10-100 molecules per cell) within plants.<ref name="Heazlewood_2012">Template:Cite book</ref> For example, using mass spectrometry on plant protein mixtures would result in multiple intense RuBisCO subunit peaks that interfere and hide those of other proteins.
Recently, one efficient method for precipitating out RuBisCO involves the usage of protamine sulfate solution.<ref>Template:Cite book</ref> Other existing methods for depleting RuBisCO and studying lower abundance proteins include fractionation techniques with calcium and phytate,<ref>Template:Cite journal</ref> gel electrophoresis with polyethylene glycol,<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> affinity chromatography,<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> and aggregation using DTT,<ref>Template:Cite journal</ref> though these methods are more time-consuming and less efficient when compared to protamine sulfate precipitation.<ref name="Heazlewood_2012" />
Evolution of RuBisCOEdit
Phylogenetic studiesEdit
The chloroplast gene rbcL, which codes for the large subunit of RuBisCO has been widely used as an appropriate locus for analysis of phylogenetics in plant taxonomy.<ref>Template:Cite journal</ref>
OriginEdit
Template:Missing information Non-carbon-fixing proteins similar to RuBisCO, termed RuBisCO-like proteins (RLPs), are also found in the wild in organisms as common as Bacillus subtilis. This bacterium has a rbcL-like protein with a 2,3-diketo-5-methylthiopentyl-1-phosphate enolase function, part of the methionine salvage pathway.<ref>Template:Cite journal</ref> Later identifications found functionally divergent examples dispersed all over bacteria and archaea, as well as transitionary enzymes performing both RLP-type enolase and RuBisCO functions. It is now believed that the current RuBisCO evolved from a dimeric RLP ancestor, acquiring its carboxylase function first before further oligomerizing and then recruiting the small subunit to form the familiar modern enzyme.<ref name = "Erb_2018" /> The small subunit probably first evolved in anaerobic and thermophilic organisms, where it enabled RuBisCO to catalyze its reaction at higher temperatures.<ref>Template:Cite journal</ref> In addition to its effect on stabilizing catalysis, it enabled the evolution of higher specificities for Template:CO2 over O2 by modulating the effect that substitutions within RuBisCO have on enzymatic function. Substitutions that do not have an effect without the small subunit suddenly become beneficial when it is bound. Furthermore, the small subunit enabled the accumulation of substitutions that are only tolerated in its presence. Accumulation of such substitutions leads to a strict dependence on the small subunit, which is observed in extant Rubiscos that bind a small subunit.
C4Edit
With the mass convergent evolution of the C4-fixation pathway in a diversity of plant lineages, ancestral C3-type RuBisCO evolved to have faster turnover of Template:CO2 in exchange for lower specificity as a result of the greater localization of Template:CO2 from the mesophyll cells into the bundle sheath cells.<ref>Template:Cite journal</ref> This was achieved through enhancement of conformational flexibility of the “open-closed” transition in the Calvin cycle. Laboratory-based phylogenetic studies have shown that this evolution was constrained by the trade-off between stability and activity brought about by the series of necessary mutations for C4 RuBisCO.<ref name="Studer_2014">Template:Cite journal</ref> Moreover, in order to sustain the destabilizing mutations, the evolution to C4 RuBisCO was preceded by a period in which mutations granted the enzyme increased stability, establishing a buffer to sustain and maintain the mutations required for C4 RuBisCO. To assist with this buffering process, the newly-evolved enzyme was found to have further developed a series of stabilizing mutations. While RuBisCO has always been accumulating new mutations, most of these mutations that have survived have not had significant effects on protein stability. The destabilizing C4 mutations on RuBisCO has been sustained by environmental pressures such as low Template:CO2 concentrations, requiring a sacrifice of stability for new adaptive functions.<ref name="Studer_2014" />
History of the termEdit
The term "RuBisCO" was coined humorously in 1979, by David Eisenberg at a seminar honouring the retirement of the early, prominent RuBisCO researcher, Sam Wildman, and also alluded to the snack food trade name "Nabisco" in reference to Wildman's attempts to create an edible protein supplement from tobacco leaves.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
The capitalization of the name has been long debated. It can be capitalized for each letter of the full name (Ribulose-1,5 bisphosphate carboxylase/oxygenase), but it has also been argued that is should all be in lower case (rubisco), similar to other terms like scuba or laser.<ref name="Sharkey_2018" />
See alsoEdit
Template:Col-begin Template:Col-1-of-2
- C4 carbon fixation
- Crassulacean acid metabolism/CAM photosynthesis
- Carboxysome
ReferencesEdit
Template:Notelist Template:Reflist
Further readingEdit
External linksEdit
- {{#invoke:citation/CS1|citation
|CitationClass=web }}