Subunit polypeptide composition of rubisco and the origin of allopolyploid Arabidopsis suecica (Brassicaceae)

The polypeptide composition of the large and small subunits of Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) from Arabidopsis thaliana, A. suecica and Cardaminopsis arenosa have been studied by IEF (isoelectric focusing) analysis. The putative recent alopolyploid origin of A. suecica is supported. The chloroplast encoded large subunits served to identify solely A. thaliana as the maternal parent whereas the nuclear encoded small subunits indicate C. arenosa as the paternal species.     

Isolation and partial amino acid sequencing of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase from three species of orchid

Small subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) have been purified from 3 species of orchid in the genus Cymbidium by gel filtration followed by preparative sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and electroelution. The samples were subjected to amino acid composition analysis and partial N-terminal amino acid sequencing. The sequencing data clearly confirm that one of the species examined is the hybrid offspring of a cross between the other two.     

Synthesis of active Olisthodiscus luteus ribulose-1,5-bisphosphate carboxylase in Escherichia coli

The ribulose-1,5-bisphosphate carboxylase (Rubisco) large- and small-subunit genes are encoded on the chloroplast genome of the eukaryotic chromophytic alga Olisthodiscus luteus. Northern blot experiments indicate that both genes are co-transcribed into a single (>6 kb) mRNA molecule. Clones from the O. luteus rbc gene region were constructed with deleted 5 non-coding regions and placed under control of the lac promoter, resulting in the expression of high levels of O. luteus Rubisco large and small subunits in Escherichia coli. Sucrose gradient centrifugation of soluble extracts fractionated a minute amount of carboxylase activity that cosedimented with native hexadecameric O. luteus Rubisco. Most of the large subunit synthesized in E. coli appeared insoluble or formed an aggregate with the small subunit possessing an altered charge: mass ratio compared to the native holoenzyme. The presence in O. luteus of a polypeptide that has an identical molecular mass and cross reacts with antiserum generated against pea large-subunit binding protein may indicate that a protein of similar function is required for Rubisco assembly in O. luteus.     

Phylogeny of gymnosperms inferred fromrbcL gene sequences

Partial nucleotide sequences of the large subunit of ribulose-1,5-bisphosphate carboxylase (rubisco) gene (1333 base pairs: about 90% of the gene) from several seed plants were determined. Phylogenetic trees based on amino acid sequences were inferred by using the neighbor joining and maximum likelihood methods. The results indicate (1) monophyly of gnetum group (Ephedra, Gnetum, Welwitschia), (2) monophyly of extant gymnosperms containing gnetum group, which contradicts the results of morphological data.     

Towards an explanation of carboxylation/oxygenation bifunctionality in Rubisco. Transition structure for the carboxylation reaction of 2,3,4-pentanetriol

We construct a theoretical model of the transition structure for the carboxylation reaction of ribulose-1,5-biphosphate catalyzed by Rubisco. This is a first-order saddle point on the energy hypersurface for the nucleophilic attack of carbon dioxide on CH₃-(CHOH)₃-CH₃ at the C2 center.Ab initio analytical gradients methods at a 4-31G basis set level are used.The carbon framework and oxygens of the stationary structure superpose with the corresponding atoms of 2-carboxyarabinitol-1,5-biphosphate, which is a transition state analog that has recently been highly refined with X-ray methods. The hydroxyl group in C3 iscis to the C2 oxygen. The C3 center is somewhat pyramidized, the dienol O2-C2-C3-O3 is not planar.The geometry of the transition state allows for simple explanations of both the enolization of Rubisco's substrate ribulose-1,5-biphosphate, O₃PO-CH2-CO-(CHOH)₂-CH₂-OPO₃ and oxygenation reaction. The former is due to the pyramidal deformation at C3 and out of plane of O2-C2-C3-O3 framework: the enoliation is intramolecular and is probably enhanced by proton tunnelling. The latter is related with the fact that a rotation around an ethylene-like bond brings the triplet state down in energy. The reactive skeleton has a stationary geometry in the triplet state not very different from the one obtained in the global transition structure. There, the triplet is only 9 kcal/mol above the singlet. The spin densities at C2 and C3 centers clearly indicate the place where oxygenation will take place.     

Amino-acid-transport mutant of Nicotiana tabacum L.

The structure of spinach ribulose 1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) has been investigated by tilted-view electron microscopy of negatively stained monolayer crystals and image processing. The structure determined consists of a cylinder of octagonal cross-section with a large central hole. Based on this and other available evidence a model for the arrangement of the large and small subunits is suggested with the eight small subunits arranged equatorially around the core of eight large subunits.Abbreviations LS large subunit - Rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase - SS small subunit     

Genetic analyses of Oryza species by molecular markers for chloroplast genomes

Summary Relationships in a wide range of Oryza species (13 species) were analyzed using the large subunits (LS) of Fraction I protein (Rubisco) and the Bam HI restriction patterns of chloroplast DNA (ctDNA) as molecular markers. Four types of LS were detected by isoelectrofocusing with and without S-carboxymethylation. The close relation between AA and CCDD genome species was suggested by analyses of LS and ctDNA. Intraspecific variation in O. latifolia was detected at the levels of both LS and ctDNA. The LS of the BB, BBCC, and CC genomes and FF (O. brachyantha) were not distinguishable, although the native Rubisco of the latter was slightly different from those of the first three. It was also shown that O. australiensis, the only EE genome species, might have evolved differently than the other Oryza species.     

Ribulose bisphosphate carboxylase in algae: synthesis,enzymology and evolution

Studies demonstrating differences in chloroplast structure and biochemistry have been used to formulate hypotheses concerning the origin of algal plastids. Genetic and biochemical experiments indicate that significant variation occurs in ribulose-1,5-bisphosphate carboxylase (Rubisco) when supertaxa of eukaryotic algae are compared. These differences include variations in the organelle location of the genes and their arrangement, mechanism of Rubisco synthesis, polypeptide immunological reactivity and sequence, as well as efficacy of substrate (ribulose bisphosphate and CO₂) binding and inhibitor (6-phosphogluconate) action. The structure-function relationships observed among chromophytic, rhodophytic, chlorophytic and prokaryotic Rubisco demonstrate that: (a) similarities among chromophytic and rhodophytic Rubisco exist in substrate/inhibitor binding and polypeptide sequence, (b) characteristic differences in enzyme kinetics and subunit polypeptide structure occur among chlorophytes, prokaryotes and chromophytes/rhodophytes, and (c) there is structural variability among chlorophytic plant small subunit polypeptides, in contrast to the conservation of this polypeptide in chromophytes and rhodophytes. Taxa-specific differences among algal Rubisco enzymes most likely reflect the evolutionary history of the plastid, the functional requirements of each polypeptide, and the consequences of encoding the large and small subunit genes in the same or different organelles.     

Effect of sulphate on photosynthesis in greenhouse–grown tomato plants

Sulphate accumulates in the rhizosphere of plants grown in hydroponic systems. To avoid such sulphate accumulation and promote the use of environmentally sound hydroponic systems, we examined the effects of four sulphate concentrations (0.1, 5,2, 10.4 and 20.8 m M ) on photosynthesis, ribulose-l,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) activities and related physiological processes in greenhouse–grown tomato plants ( Lycopersicon esculentum Mill. cv. Trust). The lowest sulphate concentration (0.1 m M ) significantly decreased photosynthetic capacity (P_c) and Rubisco activities on a leaf area basis. This result was supported by our data for dry matter per plant, which was low for plants in the 0.1 m M treatment. The photosynthesis-related variables such as leaf conductance, chlorophyll and soluble protein were lowest for the 0.1 m M treatment. Both total Rubisco activity and the activated ratio were reduced with this treatment. However, Rubisco activities expressed per g of protein or per g of chlorophyll were not significantly affected. These results suggest that sulphur deficiency depressed P_c– by reducing the amount of both Rubisco and chlorophyll and by causing an inactivation of Rubisco. The ratio of organic sulphur vs organic nitrogen (S/N) in plants of the 0.1 m M treatment was far below the normal values. This low S/N ratio might be accountable for the negative effect of low sulphate on P_c and plant growth. P_c and dry matter were not affected until sulphate concentration in the nutrient solution reached a high level of 20.8 m M .