Where is rubisco synthesized

These authors have shown that active carbamylated Rubisco is less sensitive to this protease than the inactive form. Already moderately elevated temperatures negatively affect the activation of Rubisco by Rubisco activase causing a lower percentage of carbamylated molecules and may, as a consequence, also alter the susceptibility of Rubisco to attack by certain proteases Feller et al.

Although often no Rubisco fragments are detected in naturally senescing leaves, typical breakdown products may accumulate in leaves or leaf segments under certain conditions Hildbrand et al. On the other hand, this polypeptide cross-reacts with antibodies raised against the large subunit of Rubisco, indicating that this band is a breakdown product of Rubisco. From more recent experiments with antibodies raised against the C- and N-terminus of the large subunit of Rubisco Fig.

The larger but not the smaller fragment also reacts with antibodies against amino acids 9—28 from the N-terminus, while both fragments are not detected with antibodies raised against the first 25 amino acids from the N-terminus. These results document that both fragments lack the N-terminus.

These fragments are similar to those reported by Yoshida and Minamikawa Under hypoxia, the small subunit of Rubisco is well maintained, although a portion of most large subunit molecules is removed Hildbrand et al.

The removal of an N-terminal portion has also been detected in wheat leaf segments incubated under conditions causing a low carbohydrate level Thoenen et al. The formation of such fragments is inhibited by E an inhibitor of cysteine endopeptidases. Furthermore, it could be shown that this cleavage occurs when the large subunits are still integrated together with the small subunits in the Rubisco holoenzyme Thoenen et al. This type of fragmentation was not observed in isolated pea chloroplasts.

The finding reported by Zhang et al. It appears likely that the observed extraplastidial cleavage is caused by a vacuolar cysteine endopeptidase, while in isolated plastids other types of peptide hydrolases e. Fragmentation of the large subunit of Rubisco in bean leaves incubated under hypoxia in darkness. The stained gel with the fragments F 1 and F 2 is shown in a. Specific antibodies raised in rabbits against a synthetic version of the first 25 amino acids from the N-terminus of the large subunit from spinach Rubisco b , against a synthetic version of amino acids 9—28 from the large subunit of wheat Rubisco c , or against a synthetic version of a sequence near the C-terminus amino acids — of the large subunit of Rubisco from wheat d were used to develop the immunoblots.

The evidence for the involvement of vacuolar peptide hydrolases in Rubisco degradation raises the question of how the plastidial substrate protein Rubisco may become accessible to the vacuolar enzyme s separated by several membranes from the stroma Yoshida and Minamikawa, ; Thoenen et al.

It has been proposed that chloroplasts Minamikawa et al. Such lipophilic globules are the counterpart to the hydrophilic spherical bodies and may be involved in the degradation of pigments or membrane proteins rather than of stromal enzymes.

The ricinosomes, organelles containing high levels of sulphydryl endopeptidase precursor, must be considered as important compartments involved in the increase of sulphydryl endopeptidase activity and of the rapid net protein degradation during senescence Gietl and Schmid, The question as to what extent Rubisco is degraded intraplastidially and extraplastidially is still open and represents a challenge for future research. Rubisco is degraded in leaves of intact plants during natural senescence as well as under various stress conditions.

Rubisco nitrogen can be exported from senescing organs in the form of amino acids or peptides via the phloem, allowing the supply of growing plant parts. However, the net degradation of Rubisco is not always well correlated with the export of nitrogen from the leaves, since free amino acids may accumulate to high levels or may be incorporated in the same organ into newly synthesized proteins in other cells or other subcellular compartments. The question of how the net degradation of Rubisco is controlled remains open.

There is not necessarily a switch allowing the initiation of Rubisco degradation. The opposite situation appears possible: the degradation of Rubisco might be the default pathway in the case of a metabolic disorder and might be initiated by a series of internal and external factors influencing leaf metabolism and interactions between organs.

If so, then the question would be: which conditions must be fulfilled to maintain the Rubisco level prior to senescence? Several laboratories presented good evidence that there is not one well-defined pathway for Rubisco degradation with well-defined proteolytic events. Depending on the actual conditions, reactive oxygen species may directly cleave the polypeptide chain, or plastidial or vacuolar enzymes may act on this stromal protein with or without prior modification.

The concentrations of solutes interacting with Rubisco may affect its susceptibility to proteolytic attack and allow a fine-tuning of the net degradation rate. From the results available today, it appears likely that under photoinhibitory conditions and when carbohydrates are available in excess the degradation inside the plastids plays a major role, and that under energy deficiency low carbohydrate levels vacuolar endopeptidases may come into play earlier.

Caution is recommended when generalizing mechanisms of Rubisco catabolism. The following questions remain to be addressed in future experiments. Antibodies against a synthetic version of the first 25 amino acids from the N-terminal region of the large subunit from spinach Rubisco were kindly provided by R Houtz and M Mulligan.

The authors thank C Reynolds for improving the English of the manuscript. Google Scholar. Google Preview. Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account. Sign In. Advanced Search. Search Menu. Article Navigation. Close mobile search navigation Article Navigation.

Volume Article Contents Abstract. Rubisco: the most abundant protein on earth. Reutilization of Rubisco nitrogen in whole plants. Rubisco degradation and redistribution of Rubisco nitrogen under altered source—sink relationships. Levels of Rubisco and Rubisco fragments under environmental stress. Fate of Rubisco at the subcellular level. Rubiscolytics: fate of Rubisco after its enzymatic function in a cell is terminated.

E-mail: urs. Oxford Academic. Iwona Anders. Tadahiko Mae. Revision received:. Select Format Select format. Permissions Icon Permissions. Chloroplast , endopeptidase , nitrogen remobilization , phloem transport , proteolysis , Rubisco , stress , vacuole.

Open in new tab Download slide. Google Scholar Crossref. Search ADS. Google Scholar PubMed. Influence of nitrogen deficiency on senescence and the amounts of RNA and proteins in wheat leaves.

Coordination of protein and mRNA abundances of stromal enzymes and abundances of the Clp protease subunits during senescence of Phaseolus vulgaris L. Solute leakage from detached plant parts of winter wheat: influence of maturation stage and incubation temperature. Solute losses from various shoot parts of field-grown wheat by leakage in the rain. Heat sensitivity of Rubisco, Rubisco activase and Rubisco binding protein in higher plants. Heat stress effects on Rubisco, Rubisco binding protein and Rubisco activase in wheat leaves.

The allocation of protein nitrogen in the photosynthetic apparatus: cost, consequences and control. Changes in nitrogen contents and in proteolytic activities in different parts of field-grown wheat ears Triticum aestivum L. Changes in gas exchange and in the activities of proteolytic enzymes during senescence of wheat leaves Triticum aestivum L. Leaf proteolytic activities and senescence during grain development of field-grown corn Zea mays L.

Senescence and protein degradation in leaf segments of young winter wheat: influence of leaf age. Specialized cellular arrangements in legume leaves in relation to assimilate transport and compartmentation—comparison of the paraveinal mesophyll. Paraveinal mesophyll of soybean leaves in relation to assimilate transfer and compartmentation. Immunohistochemical localization of specific glycopeptides in the vacuole after depodding. Effect of phloem interruption on endopeptidase and aminopeptidase activities in flag leaves of field-grown wheat.

C labelling kinetics of sucrose in glumes indicates significant refixation of respiratory CO 2 in the wheat ear. Ricinosomes: an organelle for developmentally regulated cell death in senescing plant tissues.

CO 2 , light and temperature influence senescence and protein degradation in wheat leaf segments. Identification and localization of vegetative storage proteins in legume leaves. Photosynthetic nitrogen assimilation and associated carbon and respiratory metabolism.

Rubisco and nitrogen relationships in rice. Leaf photosynthesis and plant growth. Differences between maize and rice in N-use efficiency for photosynthesis and protein allocation. Persistence of photosynthetic components and photochemical efficiency in ears of water-stressed wheat Triticum aestivum.

Degradation of ribulose-bisphosphate carboxylase by vacuolar enzymes of senescing French bean leaves: immunocytochemical and ultrastructural observations.

In vivo fragmentation of the large subunit of ribulose-1,5-bisphosphate carboxylase by reactive oxygen species in an intact leaf of cucumber under chilling-light conditions. Effects of panicle removal on the photosynthetic characteristics of the flag leaf of rice plants during the ripening stage.

Relationship between the suppression of photosynthesis and starch accumulation in the pod-removed bean. Light-induced proteolysis of stromal proteins in pea Pisum sativum L. Light-dependent degradation of stromal proteins in intact chloroplasts isolated from Pisum sativum L. The nitrogen use efficiency of C 3 and C 4 plants. Leaf nitrogen effects on the activity of carboxylating enzymes in Chenopodium album L. Rubisco: structure, regulatory interactions and possibilities for a better enzyme.

Requirements for the light-stimulated degradation of stromal proteins in isolated pea Pisum sativum L. The photosynthetic role of ears in C-3 cereals: metabolism, water use efficiency and contribution to grain yield. Ear of durum wheat under water stress: water relations and photosynthetic metabolism. Senescence in wheat leaves: is a cysteine endopeptidase involved in the degradation of the large subunit of Rubisco?

What stay-green mutants tell us about nitrogen remobilization in leaf senescence. The soybean kilodalton vegetative storage protein is a lipoxygenase that is localized in paraveinal mesophyll cell vacuoles.

Enzyme activities and products of CO 2 fixation in various photosynthetic organs of wheat and oat. All rights reserved. For Permissions, please e-mail: journals. Issue Section:. Download all slides. Comments 0. Add comment Close comment form modal. I agree to the terms and conditions. You must accept the terms and conditions.

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Advance article alerts. New issue alert. Receive exclusive offers and updates from Oxford Academic. Related articles in Web of Science Google Scholar. Rubisco in chloroplasts consists of eight large L, kd subunits and eight small S, kd ones Figure Each L chain contains a catalytic site and a regulatory site.

The S chains enhance the catalytic activity of the L chains. In fact, rubisco is the most abundant enzyme and probably the most abundant protein in the biosphere. Large amounts are present because rubisco is a slow enzyme; its maximal catalytic rate is only 3 s Tracing the Fate of Carbon Dioxide.

Radioactivity from 14 CO 2 is incorporated into 3-phosphoglycerate within 5 s in irradiated cultures of algae. After 60 s, the radioactivity appears in many compounds, the intermediates within the Calvin cycle. Structure of Rubisco. The active sites more Rubisco requires a bound divalent metal ion for activity, usually magnesium ion. Like the zinc ion in the active site of carbonic anhydrase Section 9.

The formation of the carbamate is facilitated by the enzyme rubisco activase , although it will also form spontaneously at a lower rate. The metal center plays a key role in binding ribulose 1,5-bisphosphate and activating it so that it will react with CO 2 Figure This complex is readily deprotonated to form an enediolate intermediate. This reactive species, analogous to the zinc-hydroxide species in carbonic anhydrase Section 9.

Role of the Magnesium Ion in the Rubisco Mechanism. Ribulose 1,5-bisphosphate binds to a magnesium ion that is linked to rubisco through a glutamate residue, an aspartate residue, and the lysine carbamate. The coordinated ribulose 1,5-bisphosphate gives more Formation of 3-Phosphoglycerate. The overall pathway for the conversion of ribulose 1,5 bisphosphate and CO 2 into two molecules of 3-phosphoglycerate.

Although the free species are shown, these steps take place on the magnesium ion. Thus, rubisco also catalyzes a deleterious oxygenase reaction. The products of this reaction are phosphoglycolate and 3-phosphoglycerate Figure The oxygenase reaction, like the carboxylase reaction, requires that lysine be in the carbamate form. Because this carbamate forms only in the presence of CO 2 , this property would prevent rubisco from catalyzing the oxygenase reaction exclusively when CO 2 is absent.

A Wasteful Side Reaction. The reactive enediolate intermediate on rubisco also reacts with molecular oxygen to form a hydroperoxide intermediate, which then proceeds to form one molecule of 3-phosphoglycerate and one molecule of phosphoglycolate. Phosphoglycolate is not a versatile metabolite. A salvage pathway recovers part of its carbon skeleton Figure A specific phosphatase converts phosphoglycolate into glycolate , which enters peroxisomes also called microbodies ; Figure Glycolate is then oxidized to glyoxylate by glycolate oxidase, an enzyme with a flavin mononucleotide prosthetic group.

Transamination of glyoxylate then yields glycine. The ammonia, used in the synthesis of nitrogen-containing compounds, is salvaged by glutamine synthetase reaction. Photorespiratory Reactions.

Phosphoglycolate is formed as a product of the oxygenase reaction in chloroplasts. After dephosphorylation, glycolate is transported into peroxisomes where it is converted into glyoxylate and then glycine. In mitochondria, more Sue Ellen Frederick. This salvage pathway serves to recycle three of the four carbon atoms of two molecules of glycolate.

However, one carbon atom is lost as CO 2. This process is called photorespiration because O 2 is consumed and CO 2 is released. Moreover, the oxygenase activity increases more rapidly with temperature than the carboxylase activity, presenting a problem for trop-ical plants Section Evolutionary processes have presumably enhanced the preference of rubisco for carboxylation.

For instance, the rubisco of higher plants is eightfold as specific for carboxylation as that of photosynthetic bacteria. The 3-phosphoglycerate product of rubisco is next converted into three forms of hexose phosphate: glucose 1-phosphate, glucose 6-phosphate, and fructose 6-phosphate. Recall that these isomers are readily interconvertible Sections The steps in this conversion Figure Alternatively, the glyceraldehyde 3-phosphate can be transported to the cytosol for glucose synthesis.

Hexose Phosphate Formation. The third phase of the Calvin cycle is the regeneration of ribulose 1,5-bisphosphate, the acceptor of CO 2 in the first step. The problem is to construct a five-carbon sugar from six-carbon and three-carbon sugars. A transketolase and an aldolase play the major role in the rearrangement of the carbon atoms. The transketolase , which we will see again in the pentose phosphate pathway Section We will consider the mechanism of transketolase when we meet it again in the pentose phosphate pathway Section Aldolase , which we have already encountered in glycolysis Section This enzyme is highly specific for dihydroxyacetone phosphate, but it accepts a wide variety of aldehydes.

With these enzymes, the construction of the five-carbon sugar proceeds as shown in Figure Formation of Five-Carbon Sugars. First, transketolase converts a six-carbon sugar and a three-carbon sugar into a four-carbon sugar and a five-carbon sugar. Then, aldolase combines the four-carbon product and a three-carbon sugar to form a seven-carbon more