Protein composition of the carboxysomes of Thiobacillus neapolitanus

For purifying carboxysomes of Thiobacillus neapolitanus an isolation procedure was developed which resulted in carboxysomes free from whole cells, protoplasts and cell fragments. These purified carboxysomes are composed of 8 proteins and at the most of 13 polypeptides. The two most abundant proteins which make up more than 60% of the carboxysomes, are ribulose-1,5-bisphosphate carboxylase and a glycoprotein with a molecular weight of 54,000. The shell of the carboxysomes consists of four glycoproteins, one also with a molecular weight of 54,000. The other proteins are present in minor quantities. Ribulose-1,5-bisphosphate carboxylase is the only enzyme which could be detected in the carboxysomes and 3-phosphoglycerate was the only product formed during incubation with ribulose-1,5-diphosphate and bicarbonate. The supernatant of a broken and centrifuged carboxysome suspension contained the large subunit of ribulose-1,5-bisphosphate carboxylase. The small subunit of ribulose-1,5-bisphosphate carboxylase was found in the pellet together with the shell proteins which indicates that the small subunit of ribulose-1,5-bisphosphate carboxylase is connected to the shell.Abbreviations RuBisCO ribulose-1,5-bisphosphate carboxylase - PMSF phenylmethylsulfonyl fluoride - PAA gelectrophoresis, polyacrylamide gelelectrophoresis - SDS sodium dodecyl sulphate - CIE crossed immunoelectrophoresis - IEF isoelectric focusing     

The Association of d-Ribulose- 1,5-Bisphosphate Carboxylase/Oxygenase with Phosphoribulokinase

When Ribulose- 1,5-bisphosphate carboxylase/oxygenase was purified from spinach leaves (Spinacia oleracea) using precipitation with polyethylene glycol and MgCl₂ followed by DEAE cellulose chromatography, 75% of phosphoribulokinase and 7% of phosphoriboisomerase activities copurified with ribulose- 1,5-bisphosphate carboxylase/oxygenase. This enzyme preparation showed ribose-5-phosphate and ribulose-5-phosphate dependent carboxylase and oxygenase activities which were nearly equivalent to its corresponding ribulose- 1,5-bisphosphate dependent activity. The ribose-5-phosphate and ribulose-5-phosphate dependent reaction rates were stable and linear for much longer time periods than the ribulose- 1,5-bisphosphate dependent rates. When sucrose gradients were used to purify ribulose- 1,5-bisphosphate carboxylase/oxygenase from crude stromal extracts, phosphoribulokinase was found to cosediment with ribulose- 1,5-bisphosphate carboxylase. Under these conditions most of the phosphoriboisomerase activity remained with the slower sedimenting proteins. Ammonium sulfate precipitation resulted in separation of the ribulose- 1,5-bisphosphate carboxylase peak from phosphoribulokinase peak. Crude extracts of peas Pisum sativum and spinach contained 0.725 to 0.730 milligram of phosphoribulokinase per milligram of chlorophyll, respectively, based on an enzyme-linked immunosorbent assay.     

Interactions between ribulose-1,5-bisphosphate carboxylase and stromal metabolites. II. Corroboration of the role of this enzyme as a metabolite buffer

The capacity of ribulose-1,5-bisphosphate carboxylase to bind reversibly chloroplast metabolites which are the substrates for both thylakoid and stromal enzymes was assessed using spinach chloroplasts and chloroplast extracts and with pure wheat ribulose-1,5-bisphosphate carboxylase. Measurements of the rate of coupled electron flow to methyl viologen in ‘leaky’ chloroplasts (which retained the chloroplast envelope and stromal enzymes but which were permeable to metabolites) and also with broken chloroplasts and washed thylakoids were used to study the effects of binding ADP and inorganic phopshate to ribulose-1,5-bisphosphate carboxylase. The presence of ribulose-1,5-bisphosphate carboxylase significantly altered the values obtained for apparent K_m for inorganic phosphate and ADP of coupled electron transport. The K_m (P_i) in washed thylakoids was 60–80 μM, in ‘leaky’ chloroplasts it was increased to 180–200 μM, while in ‘leaky’ chloroplasts preincubated with KCN and ribulose 1,5-bisphosphate the value was decreased to 40–50 μM. Similarly, the K_m (ADP) of coupled electron transport in washed thylakoids was 60–70 μM, in ‘leaky’ chloroplasts it was 130–150 μM and with ‘leaky’ chloroplasts incubated in the presence of KCN and ribulose 1,5-bisphosphate a value of 45–50 μM was obtained. The ability of ribulose 1,5-bisphosphate carboxylase to reduce the levels of free glycerate 3-phosphate in the absence of ribulose 1,5-bisphosphate was examined using a chloroplast extract system by varying the concentrations of stromal protein or purified ribulose 1,5-bisphosphate carboxylase. The effect of binding glycerate 3-phosphate to ribulose-1,5-bisphosphate carboxylase on glycerate 3-phosphate reduction was to reduce both the rate an the amount of NADPH oxidation for a given amount of glycerate 3-phosphate added. The addition of ribulose 1,5-bisphosphate reinitiated NADPH oxidation but ATP or NADPH did not. Incubation of purified ribulose-1,5-bisphosphate carboxylase with carboxyarabinitolbisphosphate completely inhibited the catalytic activity of the enzyme and decreased inhibition of glycerate-3-phosphate reduction. Two binding sites with different affinities for glycerate 3-phosphate were observed with pure ribulose-1,5-bisphosphate carboxylase.     

Isolation and partial characterization of pyrenoids from the brown alga Pilayella littoralis (L.) Kjellm.

In order to isolate high yields of pyrenoids from the brown alga Pilayella littoralis it is necessary to pretreat them with 0.1% HgCl₂ in sea water for 3 h. Without this pretreatment there is a substantial loss of pyrenoid ground substance and yields are low. Pyrenoid fractions of high purity have been obtained using silica sol gradients. A partial characterization has shown the pyrenoid to be proteinaceous and lacking chlorophyll. SDS polyacrylamide gel electrophoresis has shown that the majority of protein present is accounted for by two polypeptides which resemble the large and small subunits of ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39).Abbreviations DTT dithiothreitol - HEPES N-2-hydroxyethylniperazine N¹-2-ethanesulfonic acid - PEG polyethylene glycol - PVPP polyvinylpolypyrrolidone - RuBP ribulose-1,5-bisphosphate - RuBPCase ribulose-1,5-bisphosphate carboxylase - SDS sodium dodecyl sulphate     

Comparison of Properties of the Proteolytic Degradation of Unassembled Nuclear-encoded Subunits of Ribulose-1,5-bisphosphate Carboxylase and of the Coupling Factor of Photophosphorylation CF1*

The proteolytic degradation of unassembled small subunit polypeptides of ribulose-1,5-bisphosphate carboxylase and of the δ-subunit of the coupling factor of photophosphorylation CF₁ were analyzed and compared in vitro in the presence of stroma or membrane preparations from ribosome-deficient plastids isolated from 32°C-grown rye leaves (Secale cereale L.). Extracts obtained from 70S ribosome-deficient rye leaves after radioactive labeling were used as substrate source for the unassembled polypeptides. Soluble stroma as well as membrane preparations from isolated plastids contained proteolytic activities catalyzing the degradation of both the small subunits of ribulose-1,5-bisphosphate carboxylase and CF₁-δ in vitro. Maximal in vitro degradation was observed at pH 2–3 for the unassembled small subunits, but at pH 6–7 for the purified holoprotein of ribulose-1,5-bisphosphate carboxylase, and at pH 6.0 for unassembled CF₁-δ. Degradation of unassembled small subunits of ribulose-1,5-bisphosphate carboxylase at pH 3.0 was stimulated by Cu²⁺ but not by Ca²⁺, Mg²⁺ or ATP. At pH 3.0 the degradation of unassembled small subunits of ribulose-1,5-bisphosphate carboxylase was not inhibited by various protease inhibitors but was even stimulated. At pH 7.0 its degradation was inhibited by HgCl₂ and diazoacetyl nor-leucine methyl ester + Cu-acetate. The degradation of CF₁-δ was markedly inhibited by phenylmethylsulphonyl fluoride (PMSF) and to a lesser extent by 1,10-phenanthroline. According to present results different proteolytic systems appear to be involved in the degradation of unassembled small subunits of ribulose-1,5-bisphosphate carboxylase and of unassembled CF₁-δ.     

Carbon metabolism enzymes and photosynthesis in transgenic tobacco (Nicotiana tabacum L.) having excess phytochrome

J.M. Keller et al. (1989, EMBO J. 8, 1005–1012) introduced a phytochrome gene controlled by a cauliflower mosaic virus 35S promoter into tobacco (Nicotiana tabacum L.) providing material to test whether several photosynthesis enzymes can be increased by one modification to the plant. We report here that this transgenic tobacco had greater amounts of all enzymes examined as well as greater amounts of total protein and chlorophyll per unit leaf area. Fructose bisphosphatase (E.C. 3.1.3.11), glyceraldehyde 3-phosphate dehydrogenase (E.C. 1.2.1.12), and sucrose-phosphate synthase (E.C. 2.4.1.14) were also higher when expressed per unit protein. However, ribulose-1,5-bisphosphate carboxylase (E.C. 4.1.1.39) amount per unit leaf protein was the same in transgenic and wild-type (WT) plants. Photosynthesis in the transgenic plants was lower than in WT at air levels of CO₂, but higher than in WT above 1000 bar CO₂. The photosynthesis results indicated a high resistance to CO₂ diffusion in the mesophyll of the transgenic plants. Examination of electron micrographs showed that chloroplasts in the transgenic plants were often cup-shaped, preventing close association between chloroplast and cell surface. Chloroplast cupping may have caused the increase in the mesophyll resistance to CO₂ diffusion. We conclude that it is possible to affect more than one enzyme with a single modification, but unexpected physical modifications worsened the photosynthetic performance of this plant.Abbreviations CABP 2-carboxyarabitinol 1,5-bisphosphate - FBP fructose-1,6-bisphosphate - FBPase fructose-1,6-bisphosphatase - GAP glyceraldehyde 3-phosphate - Rubisco ribulose-1,5-bisphosphate carboxylase - SPS sucrose-phosphate synthase - WT wild type This research was supported by U.S. Department of Energy contracts DE-FG02-87ER60568 to T.D.S. and DE-FG02-88ER 13968 to R.D.V. We thank Drs. Joel Cherry and Howard P. Hershey for assistance with the transgenic plants.     

Pyrenoid protein from the brown alga Pilayella littoralis

Characterization by peptide mapping and amino acid analysis of the two major pyrenoid polypeptides from the brown alga Pilayella littoralis shows that they are very similar to the subunits of ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) from this alga. The observed similarities are discussed in relation to previous pyrenoid protein characterization from members of the Chlorophyceae.Abbreviations DTT dithiothreitol - EDTA Na₂ ethylenediamine tetraacetic acid (disodium salt) - PMFS phenylmethylsul-phonylfluoride - PVPP polyvinylpyrrolidone - RuBP ribulose-1,5-bisphosphate - RuBPCase ribulose-1,5-bisphosphate carboxylase - SDS sodium dodecyl sulphate - SDS-PAGE sodium dodecyl sulphate polyacrylamide gel electrophoresis - TRIS 2-amino-2-(hydroxymethyl) propane-1,3-diol - TPCK L-1-tosylamido-2-phenylethylchoromethyl ketone     

Reversible heat-inactivation of the calvin cycle: A possible mechanism of the temperature regulation of photosynthesis

Photosynthetic CO₂ fixation rates in leaves and intact chloroplasts of spinach measured at 18°–20° C are substantially decreased by pretreatment at temperatures exceeding 20° C. Mild heating which causes 80% inhibition of CO₂ fixation does not affect phosphoglyceroacid reduction and causes increases in the ATP/ADP ratio and the light-induced transthylakoid proton gradient. The inactivation of the CO₂ fixation is completely reversible with half-times of recovery in the order of 15–20 min. Comparison of steady-state patterns of ¹⁴C labeled Calvin cycle intermediates of heat-treated and control samples reveals a large increase in the ribulose-1,5-bisphosphate/phosphoglyceroacid ratio and a large decrease in the phosphoglyceroacid/triosephosphate ratio. It is concluded that inactivation of CO₂ fixation occurring at elevated temperatures is caused by inhibition of the ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39). Measurements of light-induced light scattering changes of thylakoids and of the light-induced electrochromic absorption shift show that these signals are affected by mild heating in a way which is strictly correlated with the inactivation of the CO₂ fixation. It is proposed that the function of the ribulose-1,5-bisphosphate carboxylase in vivo requires a form of activation that involves properties of the thylakoid membrane which are affected by the heat treatment. The fact that these changes in thylakoid membrane properties and of ribulose-1,5-bisphosphate carboxylase activity are already affected at elevated temperatures which can still be considered physiological, and the reversible nature of these changes, suggest that they may play a role in temperature regulation of the overall photosynthetic process.Abbreviations 9-AA 9-aminoacridine - DMO 5,5-dimethyloxazolidine-2,4-dione - FBP fructose-1,6-bisphosphate - HEPES N-2-hydroxyethylpiperazine N-2-ethane sulfonic acid - HMP hexose monophosphates - PGA 3-phosphoglycerate - PMP pentose monophosphates - RuBP ribulose-1,5-bisphosphate - SBP seduheptulose-1,7-bisphosphate - TP triose monophosphates     

The drelationship between CO2-assimilation rate,Rubisco carbamylation and Rubisco activase content in activase-deficient transgenic tobacco suggests a simple model of activase action

Transgenic tobacco (Nicotiana tabacum L. cv. W38) plants with an antisense gene directed against the mRNA of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) activase were used to examine the relationship between CO₂-assimilation rate, Rubisco carbamylation and activase content. Plants used were those members of the r₁ progeny of a primary transformant with two independent T-DNA inserts that could be grown without CO₂ supplementation. These plants had from < 1% to 20% of the activase content of control plants. Severe suppression of activase to amounts below 5% of those present in the controls was required before reductions in CO₂-assimilation rate and Rubisco carbamylation were observed, indicating that one activase tetramer is able to service as many as 200 Rubisco hexadecamers and maintain wild-type carbamylation levels in vivo. The reduction in CO₂-assimilation rate was correlated with the reduction in Rubisco carbamylation. The anti-activase plants had similar ribulose-1,5-bisphosphate pool sizes but reduced 3-phosphoglycerate pool sizes compared to those of control plants. Stomatal conductance was not affected by reduced activase content or CO₂-assimilation rate. A mathematical model of activase action is used to explain the observed hyperbolic dependence of Rubisco carbamylation on activase content.Abbreviations CA1P 2-carboxyarabinitol-1-phosphate - P_ip_a intercellular, ambient partial pressure of CO₂ - PGA 3-phospho-glycerate - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose-1,5-bisphosphate - SSU small subunit of Rubisco     

A point mutation in the N-terminus of ribulose-1,5-bisphosphate carboxylase affects ribulose-1,5-bisphosphate binding

Mutagenesis in vitro of the gene encoding the large subunit of ribulose-1,5-bisphosphate carboxylase/ oxygenase (EC 4.1.1.39) from Anacystis nidulans was used to generate novel enzymes. Two conserved residues, threonine 4 and lysine 11 in the N-terminus were changed. The substitution of threonine 4 with serine or valine had little effect on the kinetic parameters. The substitution of lysine 11 with leucine, which is non-polar, increased the K _m for ribulose-1,5-bisphosphate from 82 to 190 M but its replacement with glutamine, which has polar properties, had no appreciable effect.Abbreviations Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose-1,5-bisphosphate - LSU large sub-unit of Rubisco - SSU small subunit of Rubisco We thank Dr. S. Gutteridge (DuPont, Wilmington, USA) for structural information and for his comments on the results described. The technical assistance of Mr. A. Cowland and Mr. I. Major was invaluable.     

Mutations in loop six of the large subunit of ribulose-1,5-bisphosphate carboxylase affect substrate specificity

Mutagenesis in vitro of the gene encoding the large subunit of ribulose-1,5-bisphosphate carboxylase/ oxygenase (EC 4.1.1.39) from Anacystis nidulans Synechococcus PCC 6301) was used to generate novel enzymes in Escherichia coli. Residues in C-terminal loop 6 of the / barrel structure of the large subunit were changed. Replacement of valine 331 with alanine caused a 90% reduction in V _max but did not alter the enzyme's relative specificity towards either of its gaseous substrates, CO₂ and O₂. However replacement of alanine 340 with glutamate decreased the enzyme's specificity for CO₂ but had no significant effect on either the K _m for ribulose-1,5-bisphosphate or CO₂ or on V _max. In contrast replacing a small cassette of residues 338-341 produced a small increase in the specificity factor.Abbreviations Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose-1,5-bisphosphate - CABP 2-carbox-yarabinitol-1,5-bisphosphate We thank Karen Moore for the statistical analysis of the specificity factors. We acknowledge helpful discussions with Jim Pitts and Richard Pickersgill. This work was aided by the invaluable technical assistance of Iain Major.     

Mass-spectrometric evidence for the double-carboxylation pathway of malate synthesis by Crassulacean acid metabolism plants in light

Phyllodia of the Crassulacean acid metabolism (CAM) plant Kalanchoë tubiflora were allowed to fix ¹³CO₂ in light and darkness during phase IV of the diurnal CAM cycle, and during prolongation of the regular light period. After ¹³CO₂ fixation in darkness, only singly labelled [¹³C]malate molecules were found. Fixation of ¹³CO₂ under illumination, however, produced singly labelled malate as well as malate molecules which carried label in two, three or four carbon atoms. When the irradiance during ¹³CO₂ fixation was increased, the proportion of singly labelled malate decreased in favour of plurally labelled malate. The irradiance, however, did not change either the ratio of labelled to unlabelled malate molecules found in the tissue after the ¹³CO₂ application, or the magnitude of malate accumulation during the treatment with label. The ability of the tissue to store malate and the labelling pattern changed throughout the duration of the prolonged light period. The results indicate that malate synthesis by CAM plants in light can proceed via a pathway containing two carboxylation steps, namely ribulose-1,5-bisphosphate-carboxylase/oxygenase (EC 4.1.1.39) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) which operate in series and share common intermediates. It can be concluded that, in light, phosphoenolpyruvate carboxylase can also synthesize malate independently of the proceeding carboxylation step by ribulose-1,5-bisphosphate carboxylase/oxygenase.Abbreviations CAM Crassulacean acid metabolism - PEP phosphoenolpyruvate - PEPCase phosphoenolpyruvate carboxylase (EC 4.1.1.31) - RuBPCase ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) - TMS trimethylsilyl     

Effect of growth conditions on carboxylating enzymes of Zea mays plants

Phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) and ribulose-1,5-bisphospate (RuBP) carboxylase (EC 4.1.1.39) activities in leaves of different maize hybrids grown under field conditions (high light intensity) and in a growth chamber (low light intensity) were determined. Light intensity and leaf age affected PEP carboxylase activity, whereas RuBP carboxylase was affected by leaf age only at low light intensity. PEP carboxylase/RuBP carboxylase activity ratio decreased according to light intensity and leaf age. Results demonstrate that Zea mays grown under field conditions is a typical C₄ species in all leaves independently from their position on the stem, whereas it may be a C₃ plant when it is grown in a growth chamber at low light intensityAbbreviations PEP phosphoenolpyruvate - RuBP ribulose-1,5-bisphosphate     

Ribulose-1,5-bisphosphate carboxylase-deficient plastome mutants of Oenothera

In spite of only slightly subnormal pigment contents, two plastome mutants of Oenothera (Vα, Iσ) were practically incapable of photosynthetic CO₂ fixation and another one exhibited considerably reduced photosynthesis (IVβ). While other photosynthetic enzymes were present as far as investigated, ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) activity was very low or missing altogether. As shown by gel electrophoresis, mutant IVβ contained some, though little, fraction I protein. In the other two mutants fraction I protein could not be detected. Also, neither the small nor the large subunit of ribulose-1,5-bisphosphate carboxylase could be found in these mutants. In immunodiffusion experiments with a monospecific antiserum against rye ribulose-1,5-bisphosphate carboxylase, only extracts from wild-type Oenothera produced visible precipitation lines. Still, the presence of very low levels of immunochemically reactive antigen was indicated for all three mutants. The highest level was observed in mutant IVβ. The behaviour of the mutant extracts suggested that the antigens of mutant and wild type leaves reacting with the antiserum were not identical. All mutants appeared to have a coupled electron transport system as shown by ATP measurements, light scattering and 515 nm absorption changes. Linear electron transport was possible in the mutants. Still, the photoresponse of cytochrome f and fluorescence measurements suggested altered electron transport properties in the mutants. These are interpreted to be secondary lesions of the photosynthetic apparatus caused by primary deficiency in ribulose-1,5-bisphosphate carboxylase activity. From the absence in two mutants (Vα, Iσ) of the small subunit of ribulose-1,5-bisphosphate carboxylase, which is known to be coded for by nuclear DNA and to be synthesized on cytoplasmic ribosomes, it appears that the genetic system of the plastids is capable of interfering with the genome-controlled synthesis of plastid components.     

The DNA-binding protease,CND41, and the degradation of ribulose-1,5-bisphosphate carboxylase/oxygenase in senescent leaves of tobacco

Plastids bear their own genome, organized into DNA–protein complexes (nucleoids). Recently, we identified a DNA-binding protease (CND41) in the chloroplast nucleoids of cultured tobacco (Nicotiana tabacum L.) cells. In this study, we examine the biochemical function of this novel DNA-binding protease, particularly in senescent leaves, because antisense tobacco with a reduced amount of CND41 showed retarded senescence. Nitrogen-depletion experiments clearly showed that CND41 antisense tobacco maintained green leaves and constant protein levels, especially ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), throughout the whole plant, whereas wild-type tobacco showed marked senescence and the reduction of protein levels in the lower leaves. In vitro analyses confirmed that CND41 showed proteolytic activity at physiological pH when denatured Rubisco was used as the substrate. These results suggest that CND41 is involved in Rubisco degradation and the translocation of nitrogen during senescence. The possible regulation of protease activity of CND41 through DNA-binding is discussed.Abbreviations CABP 2-Carboxyarabinitol-1,5-bisphosphate - CBB Coomassie Brilliant Blue - GS Glutamine synthetase - OEC33 The extrinsic 33-kDa protein in the oxygen-evolving complex - Rubisco Ribulose 1,5-bisphosphate carboxylase/oxygenase     

Water stress effects on photosynthesis in different mulberry cultivars

The effect of water stress on photosynthesis was determined in five mulberry cultivars (Morus alba L. cv. K-2, MR-2, BC2-59, S-13 and TR-10). Drought was imposed by withholding water and the plants were maintained at different water potentials ranging from 0.5 -MPa to 2.0 -MPa. Photosynthetic rates, activities of ribulose-1,5-bisphosphate carboxylase and sucrose phosphate synthase, photosystem II activity and chlorophyll content were used as key parameters to assess photosynthetic performance. There was a marked variation in the photosynthetic rates and ribulose-1,5-bisphosphate carboxylase activity among the five mulberry cultivars subjected to water stress. Photosystem II (PSII) and sucrose phosphate synthase activities were also severely reduced as measured by drought conditions. Of the five mulberry cultivars, S-13 and BC2-59 showed higher photosynthetic rates, ribulose-1,5-bisphosphate carboxylase activity, high sucrose phosphate synthase activity and photochemical efficiency of PSII compared to the other varieties.     

Carbon assimilation by different developmental stages of Laminaria saccharina

Various stages of the life cycle of the marine brown alga Laminaria saccharina (L.) Lamour. (Laminariales, Phaeophyta) including male and female gametophytes, female gametes, zygotes and young sporophytes of different age were investigated for their potentials of carbon dioxide (¹⁴CO₂) fixation. Rates of photosynthesis attain the same order of magnitude in all stages. Photosynthetic ¹⁴CO₂-fixation is accompanied by a substantial light independent carbon assimilation. This is confirmed by rate determinations of the equivalent carboxylating enzymes present in the plants, ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and phosphoenolpyruvate carboxokinase (EC 4.1.1.32) as well as by chromatographic analyses of the appropriate [¹⁴C]-assimilate patterns.Abbreviations RuBP-C ribulose-1,5-bisphosphate carboxylase - PEP-CK phosphoenolpyruvate carboxykinase - PEP phosphoenolpyruvate - PS photosynthesis - DF dark fixation     

Control analysis of photosynthetic CO2 fixation

The potential of control analysis to aid our understanding of regulation and control of photosynthetic carbon metabolism is investigated. Methods of metabolic control analysis are used to determine flux control coefficients of photosynthetic reactions from enzyme elasticities. Equations expressing control coefficients symbolically by enzyme elasticities are derived, and general properties of these expressions are analysed. Suggestions for experimental determination of flux control coefficients from enzyme elasticities are given. A simplified model of the Calvin-Benson cycle is used to illustrate interrelations between patterns of photosynthetic metabolites and that of control coefficients.Abbreviations GAPDH glyceraldehyde phosphate dehydrogenase - PGA 3-phosphoglycerate - PGK 3-phosphoglycerate kinase - Pi inorganic phosphate - PRK phosphoribulokinase - RuBP ribulose-1,5-bisphosphate(_{total, free}) - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - Ru5P ribulose-5-phosphate     

Purification and characterization of maize ribulose-1,5-bisphosphate carboxylase

The ribulose-1,5-bisphosphate carboxylase/oxygenase purified from maize (a C₄ monocot) to homogeneity has a MW of532 000 and sedimentation coeffici