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.     

Intermediates formed by the Co2+-activated ribulose-1,5-bisphosphate carboxylase/oxygenase from spinach studied by electron paramagnetic resonance spectroscopy

Two enzyme-metal-bound intermediates formed by the Co2+-activated ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) have been studied by electron paramagnetic resonance (EPR) spectroscopy. Their rates of approach to a stationary state are different and their relative amounts at steady state are dependent on the concentration of ribulose 1,5-bisphosphate. It is therefore proposed that enzyme-metal-coordinated ribulose 1,5-bisphosphate and an enzyme-metal-coordinated enediolate anion of it, where bound ribulose 1,5-bisphosphate appears first, constitute the two EPR-detectable intermediates, respectively.     

Rapid kinetics of an N-terminal mutant of cyanobacterial ribulose-1,5-bisphosphate carboxylase/oxygenase

The transient changes in absorption of visible light upon addition of ribulose 1,5-bisphosphate to Co2(+)-activated ribulose-1,5-bisphosphate carboxylase/oxygenase were used to show altered catalytic properties of a mutant form of the enzyme from Anacystis nidulans. The mutant form of the enzyme had a modified N-terminus and a 10-fold greater Km for ribulose 1,5-bisphosphate than the natural cyanobacterial enzyme.     

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.     

Ribulose 1,5-bisphosphate carboxylase and oxygenase from Thiocapsa roseopersicina: activation and catalysis.

Ribulose 1,5-bisphosphate carboxylase/oxygenase purified from malate-grown Thiocapsa roseopersicina required Mg²⁺ for the activation of both carboxylase and oxygenase activities. Mg²⁺ was either not required or required at very low concentrations for catalysis by both enzyme activities. EDTA and dithiothreitol had no effect on ribulose 1,5-biphosphate oxygenase. The K_0.5 values with respect to Mg²⁺ for activation of the carboxylase and oxygenase activities were 8.4 and 2 mm, respectively. Ribulose 1,5-biphosphate carboxylase and oxygenase activities revealed differential sensitivities to 6-phosphogluconate. This ligand at 1 mm inhibited the carboxylase activity 30%, whereas the oxygenase activity was inhibited by 69%.     

Increased susceptibility of ribulose-1,5-bisphosphate carboxylase/oxygenase to proteolytic degradation caused by oxidative treatments

The susceptibility of the chloroplastic enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase to proteolysis by trypsin, chymotrypsin, proteinase K, and papain is enhanced by oxidative treatments including spontaneous oxidation of cysteines. Proteinases exhibit a high specificity for the oxidized inactive form of the carboxylase, cleaving its large subunit. Treatment of the inactive enzyme with dithiothreitol results in partial recovery of both carboxylase activity and resistance to proteolysis. This behavior may explain the specific degradation of ribulose-1,5-bisphosphate carboxylase/oxygenase that occurs in vivo during leaf senescence.     

Derepression of the synthesis of D-ribulose 1,5-bisphosphate carboxylase/oxygenase from Rhodospirillum rubrum.

The synthesis of ribulose 1,5-bisphosphate carboxylase/oxygenase in Rhodospirillum rubrum was greatly influenced by the conditions of culture. When grown photolithotrophically in an atmosphere containing low levels of CO2 (1.5 to 2%), enzyme synthesis was derepressed, with the result that the enzyme comprised up to 50% of the soluble protein of the cells as determined by immunological quantitation. This response was not observed when R. rubrum was grown photolithotrophically in an atmosphere of 5% CO2 in hydrogen. Similarly, the derepression of ribulose 1,5-bisphosphate carboxylase/oxygenase was observed in photoheterotrophically (butyrate)-grown cultures only after the HCO3- supply was nearly exhausted. The increase in enzyme activity observed in derepressed cultures was not paralleled by an increase in the in vivo CO2 fixation rate. Apparently, R. rubrum derepresses the synthesis of ribulose 1,5-bisphosphate carboxylase/oxygenase when exposed to low CO2 concentrations to scavenge the limited CO2 available to such cultures.     

Photomodification of a serine at the active site of ribulose-1,5-bisphosphate carboxylase/oxygenase by vanadate

Irradiation of ribulose-1,5-bisphosphate carboxylase/oxygenase from spinach in the presence of vanadate at 4 degrees C resulted in rapid loss of carboxylase activity. The inactivation was light and vanadate dependent. When the enzyme was irradiated in the presence of the substrate ribulose 1,5-bisphosphate or an analogue such as fructose 1,6-bisphosphate, the inactivation was greatly reduced. Sodium bicarbonate and phosphate also protected against inactivation. No additional protection was observed in the presence of Mg2+ nor did Mg2+ alone protect. Carboxylase activity could be partially restored by treatment with NaBH4, and the photomodified protein could be tritiated with NaB3H4. Amino acid analysis showed that the tritium had been incorporated into serine. The data suggest that an active-site serine is photooxidized by vanadate to an aldehyde which results in activity loss. Irradiation in the presence of vanadate also resulted in cleavage in the large subunit of the enzyme which was subsequent to inactivation.     

Active-site histidines in recombinant cyanobacterial ribulose-1,5-bisphosphate carboxylase/oxygenase examined by site-directed mutagenesis

The functions of His²⁹¹, His²⁹⁵ and His³²⁴ at the active-site of recombinant A. nidulans ribulose-1,5-bisphosphate carboxylase/ oxygenase have been explored by site-directed mutagenesis. Replacement of His²⁹¹ by K or R resulted in unassembled proteins, while its replacement by E, Q or N resulted in assembled but inactive proteins. These results are in accord with a metal ion-binding role of this residue in the activated ternary complex by analogy to x-ray crystallographic analyses of tobacco and spinach enzymes.His³²⁴ (H327 in spinach), which is located within bonding distance of the 5-phosphate of bound bi-substrate analog 2-carboxyarabinitol 1,5-bisphosphate in the crystal structures, has been substituted by A, K, R, Q and N. Again with the exception of the H324K and R variants, these changes resulted in detectable assembled protein. The mutant H324A protein exhibited no detectable carboxylase activity, whereas the H324Q and H324N changes resulted in purifiable holoenzyme with 2.0 and 0.1% of the recombinant wild-type specific carboxylase activity, respectively. These results are consistent with a phosphate binding role for this residue.The replacement of His²⁹⁵, which has been suggested to aid in phosphate binding, with Ala in the A. nidulans enzyme leads to a mutant with 5.8% of the recombinant wild-type carboxylase activity. All other mutations at this position resulted in unassembled proteins. Purified H295A and H324Q enzymes had elevated K_m(RuBP) values and unchanged CO₂/O₂ specificity factors compared to recombinant wild-type.Abbreviations CABP D-2-carboxyarabinitol 1,5 bisphosphate - IPTG isopropyl-b-d-thiogalactopyranoside - L large subunit of rubisco - PAGE polyacrylamide gel electrophoresis - rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose-P₂, ribulose 1,5 bisphosphate - S small subunit of rubisco - SDS sodium dodecyl sulfate - X-gal 5-bromo-4-chloro-3-indolyl-b-d-galactoside     

Regulation of photosynthesis in nitrogen deficient wheat seedlings

Nitrogen effects on the regulation of photosynthesis in wheat (Triticum aestivum L., cv Remia) seedlings were examined. Ribulose 1,5-bisphosphate carboxylase/oxygenase was rapidly extracted and tested for initial activity and for activity after incubation in presence of CO₂ and Mg²⁺. Freeze clamped leaf segments were extracted for determinations of foliar steady state levels of ribulose 1,5-bisphosphate, triose phosphate, 3-phosphoglycerate, ATP, and ADP. Nitrogen deficient leaves showed increased ATP/ADP and triose phosphate/3-phosphoglycerate ratios suggesting increased assimilatory power. Ribulose 1,5-bisphosphate levels were decreased due to reduced pentose phosphate reductive cycle activity. Nevertheless, photosynthesis appeared to be limited by ribulose 1,5-bisphosphate carboxylase/oxygenase, independent of nitrogen nutrition. Its degree of activation was increased in nitrogen deficient plants and provided for maximum photosynthesis at decreased enzyme protein levels. It is suggested that ribulose 1,5-bisphosphate carboxylase/oxygenase activity is regulated according to the amount of assimilatory power.     

Phosphorylation in vitro of the large subunit of the ribulose-1,5-bisphosphate carboxylase and of the glyceraldehyde-3-phosphate dehydrogenase

A protein kinase activity responsible for the in vitro phosphorylation of at least six endogenous polypeptides including the large subunit of the ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) is present in the stroma (3000 X g supernatant, S30) of spinach chloroplasts. The phosphorylation of the ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit is strongly enhanced when sodium fluorure is used as a protein phosphatase inhibitor. Phosphorylation occurs on threonine and serine residues. The protein kinase involved is not Ca2+-dependent. There is also evidence for a protein phosphatase activity which suggests a coupled regulation by a phosphorylation-dephosphorylation process. The phosphorylating activity is drastically reduced when S30 is prepared from leaves harvested after a dark period. Phosphorylation of the ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit is not related to its own synthesis. The in vitro phosphorylation of the glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13) is also demonstrated.     

The role of enzyme activation state in limiting carbon assimilation under variable light conditions

The mechanisms regulating transient photosynthesis by soybean (Glycine max) leaves were examined by comparing photosynthetic rates and carbon reduction cycle enzyme activities under flashing (saturating 1 s lightflecks separated by low photon flux density (PFD) periods of different durations) and continuous PFD. At the same mean PFD, the mean photosynthetic rates were reduced under flashing as compared to continuous light. However, as the duration of the low PFD period lengthened, the CO₂ assimilation attributable to a lightfleck increased. This enhanced lightfleck CO₂ assimilation was accounted for by a greater postillumination CO₂ fixation occurring after the lightfleck. The induction state of photosynthesis, ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco), fructose 1,6-bisphosphatase (FBPase) and ribulose 5-phosphate kinase (Ru5P kinase) activities all responded similarly and were all lower under flashing as compared to constant PFD of the same integrated mean value. However, the fast phase of induction and FBPase and Ru5P kinase activities were reduced more than were the slow phase of induction and rubisco activity. This was consistent with the role of the former enzymes in the fast induction component that limited RuBP regeneration. Competition for reducing power between carbon metabolism and thioredoxin-mediated enzyme activation may have resulted in lower enzyme activation states and hence lower induction states under flashing than continuous PFD, especially at low lightfleck frequencies (low mean PFD).Abbreviations FBPase fructose 1,6-bisphosphatase (EC 3.1.3.11) - LUE lightfleck use efficiency - P-glycerate 3-phosphoglycerate - PICF post-illumination CO₂ fixation - Ru5P kinase ribulose 5-phosphate kinase (EC 2.7.1.19) - RuBP ribulose 1,5-bisphosphate - rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) - SBpase sedoheptulose 1,7-bisphosphatase (EC 3.1.3.37)     

香蕉rbcS基因启动子的克隆及序列分析

以巴西香蕉为材料,根据已经获得的香蕉1,5-二磷酸核酮糖羧化/加氧酶小亚基基因的全长cDNA序列设计1对专一引物,通过PCR扩增得到了香蕉1,5-二磷酸核酮糖羧化/加氧酶小亚基的基因组全长,序列长811 bp,含有2个内含子。根据其基因组序列设计引物,采用SEFA-PCR方法,以总DNA为模板克隆了香蕉1,5-二磷酸核酮糖羧化/加氧酶小亚基基因的启动子序列,长1 681 bp。用PLACE软件分析发现该序列具有启动子的基本元件TATA-box、CAAT-box,包含多个胁迫诱导元件,如光诱导元件、赤霉素、低温诱导元件、昼夜节律调控元件等。该序列的克隆与分析为进一步研究香蕉1,5-二磷酸核酮糖羧化/加氧酶小亚基基因的表达调控奠定了基础。     

Identification of the Large Subunit of Ribulose 1,5-Bisphosphate Carboxylase/Oxygenase as a Substrate for Transglutaminase in Medicago sativa L. (Alfalfa)

Extracts prepared from floral meristematic tissue of alfalfa (Medicago sativa L.) were investigated for expression of the enzyme transglutaminase in order to identify the major protein substrate for transglutaminase-directed modifications among plant proteins. The large polymorphic subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase in alfalfa, with molecular weights of 52,700 and 57,600, are major substrates for transglutaminase in these extracts. This was established by: (a) covalent conjugation of monodansylcadaverine to the large subunit followed by fluorescent detection in SDS-polyacrylamide gels; (b) covalent conjugation of [¹⁴C]putrescine to the large subunit with detection by autoradiography; (c) covalent conjugation of monodansylcadaverine to the large subunit and demonstration of immunocross-reactivity on nitrocellulose transblot of the modified large subunit with antibody prepared in rabbits against dansylated-ovalbumin; (d) demonstration of a direct dependence of the rate of transglutaminase-mediated, [¹⁴C]putrescine incorporation upon the concentration of ribulose, 1,5-bisphosphate carboxylase/oxygenase from alfalfa or spinach; and (e) presumptive evidence from size exclusion chromatography that transglutaminase may cofractionate with native molecules of ribulose 1,5-bisphosphate carboxylase/oxygenase in crude extracts. Analysis of the primary structure of plant large subunit has revealed numerous potential glutaminyl and lysyl sites for transglutaminase-directed modifications of ribulose 1,5-bisphosphate carboxylase/oxygenase.     

Rate-limiting factors in leaf photosynthesis. I. Carbon fluxes in the calvin cycle

Rates of photosynthesis of spinach leaves were varied by varying light intensity and CO₂ concentration. Metabolism of the leaves was then arrested by freezing them in liquid nitrogen. Chloroplasts were isolated by a nonaqueous procedure. In the chloroplast fractions, levels of intermediates of the carbon reduction cycle were determined and considered in relation to the photosynthetic flux situation of the leaves at the time before freezing. During induction of photosynthesis, ribulose 1,5-bisphosphate levels increased in parallel with CO₂ fixation. In the steady state, a similar relation between ribulose 1,5-bisphosphate levels and CO₂ uptake was observed at light intensities between 0 and 50 W·m⁻². A further increase in light intensity increased CO₂ fixation rates but not ribulose 1,5-bisphosphate levels. Increasing the CO₂ concentration resulted in increased CO₂ uptake, whereas ribulose 1,5-bisphosphate levels decreased. Even under CO₂ saturation, ribulose 1,5-bisphosphate levels were about 100 nmol/mg chlorophyll corresponding to about 3.5 mM ribulose 1,5-bisphosphate in the chloroplast stroma. This suggests that even under CO₂ saturation, ribulose-1,5-bisphosphate carboxylase limits photosynhetic CO₂ uptake. Mass action ratios calculated from measured metabolite levels demonstrated that the thermodynamic gradient required for the regeneration of ribulose 1,5-bisphosphate from hexosephosphate and triosephosphate increased considerably as photosynthetic flux increased. Similar calculations revealed that the enzymatic apparatus responsible for the reduction of 3-phosphoglycerate to dihydroxyacetone phosphate is not displaced much from equilibrium even under maximum rates of photosynthesis at saturating CO₂. The same is true for aldolase. Fructose-1,6-bisphosphatase also did not limit Calvin cycle turnover. Only at very low light intensities and during the first minutes of the induction period was the ratio of fructose 1,6-bisphosphate to fructose 6-phosphate high. This observation was more readily explained in terms of fructose 1,6-bisphosphate binding to ribulose-1,5-bisphosphate carboxylase than by a rate limitation imposed by insufficient activation of fructose-1,6-bisphosphatase.     

Glutamine synthetase in ribulose 1,5-bisphosphate carboxylase/oxygenase deficient tobacco mutants in cell suspension culture

In two tobacco mutants lacking ribulose, 1,5-bisphosphate carboxylase/oxygenase the amount of glutamine synthetase and its activity were determined and compared with the wild type green cells. It was shown that in these two mutants glutamine synthetase protein content was six times lower than in the wild type. This situation was comparable to that found in etiolated cells where ribulose 1,5-bisphosphate carboxylase/oxygenase was absent. These observations suggest that a common regulatory mechanism might control the dual light dependent biosynthesis of both enzymes. The results have also implications concerning the efficiency of the reassimilation of ammonia by chloroplastic glutamine synthetase during the photorespiratory process.     

Serine-376 contributes to the binding of substrate by ribulose-bisphosphate carboxylase/oxygenase from Anacystis nidulans.

Site-directed mutagenesis was used to change Ser376 in the active site of ribulose-1,5-bisphosphate carboxylase/oxygenase from the cyanobacterium Anacystis nidulans to Cys, Thr, or Ala. When expressed in Escherichia coli and purified, the mutant enzymes exhibited carboxylase activities that were reduced by 99% or more with respect to the activity of the wild-type enzyme. The Km values for ribulose bisphosphate at pH 8.0, 30 degrees C, were elevated from 46 microM for wild-type enzyme to 287, 978, and 81 microM for mutants in which Cys, Thr, or Ala, respectively, replaced Ser376. The Cys and Thr variants were almost devoid of oxygenase activity whereas the Ala variant had 16% as much oxygenase as wild-type enzyme, suggesting that this mutation had greatly elevated the oxygenase:carboxylase ratio.     

Biosynthesis of ribulose-1.5-bisphosphate carboxylase in greening cells of Euglena gracilis

Light induction of chloroplast development in Euglena leads to quantitative changes in the protein composition of the soluble cell part. One major part of these is the observed accumulation of ribulose-1.5-bisphosphate carboxylase/oxygenase (RuBPCase) enzyme (EC 4.1.1.39). As measured by immunoelectrophoresis, a small amount of RuBPCase (about 10^-6 pmol) is present in a dark-grown cell, whereas a greening cell (72h) contains 10–20 pmol enzyme. Both the cytoplasmic and chloroplastic translation inhibitors, cycloheximide and spectinomycin, have a strong inhibitory effect on the synthesis of the enzyme throughout the greening process of Euglena cells. Electrophoretic and immunological analyses of the soluble phase prepared from etiolated or greening cells do not show the presence of free subunits of the enzyme. For each antibiotic-treated greening cell, the syntheses of both subunits are blocked. Our data indicate that tight reciprocal control between the syntheses of the two classes of subunits occurs in Euglena. In particular, the RuBPCase small subunit synthesis in greening Euglena seems more dependent on the protein synthesis activity of the chloroplast than the syntheses of other stromal proteins from cytoplasmic origin.Abbreviations LSU large subunit of ribulose-1.5-bisphosphate carboxylase - RuBP ribulose-1.5-bisphosphate - RuBP-Case ribulose-1.5-bisphosphate carboxylase - SSU small subunit of ribulose-1.5-bisphosphate carboxylase     

Proline alleviates salt-stress-induced enhancement in ribulose-1, 5-bisphosphate oxygenase activity

Sodium chloride enhanced oxygenase activity while curtailing carboxylase activity of Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase; EC 4.1.1.39) purified to electrophoretic homogeneity. Exposure to 200 mM NaCl brought about an increase in the potential of Rubisco to oxygenate RuBP by over 50%. On the other hand, proline suppressed both oxygenase as well as carboxylase activities of Rubisco. Interestingly, proline-induced suppression in oxygenase activity was significantly higher than that of carboxylase activity. Most amazingly, salt-stress-induced enhancement in oxygenase activity was fully alleviated by proline even when present at a concentration as low as 50 mM. The findings presented in this communication clearly demonstrate for the first time that stress-induced proline accumulation might have a critical role in lowering the loss in fixed carbon by curtailing salt-stress-promoted enhancement in oxygenase activity of Rubisco.     

Immuno-gold localization of cytochrome f,light-harvesting complex,ATP synthase and ribulose 1,5-bisphosphate carboxylase/oxygenase

The proteins ribulose 1,5-bisphosphate carboxylase/oxygenase, ATP synthase, light-harvesting chlorophyll a/b protein, and cytochrome f, have been localized in mesophyll chloroplasts of barley (Hordeum vulgare L.) by electron microscopy of immunogold-labelled sections. The light-harvesting chlorophyll a/b protein and cytochrome f are shown to be present in the grana, both within the stacks and at the margins, and in the stromal membranes. Although the absolute amount of labelling for these proteins is greater in the grana than in the stromal membranes, when expressed as label/membrane length the partitioning appears approximately equal between appressed and non-appressed membranes for both the light-harvesting chlorophyll a/b protein and cytochrome f. ATP synthase is restricted to the non-appressed thylakoid membranes, and ribulose 1,5-bisphosphate carboxylase/oxygenase is uniformly distributed through the stromal contents.Abbreviations CF₁ ATP synthase - LHCPII light-harvesting chlorophyll a/b protein - Rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase