Ribulose 1,5-bisphosphate carboxylase/oxygenase from Pseudomonas oxalacticus

Molecular and cellular regulation of autotrophic carbon dioxide fixation in microorganisms

Images

Ribulose 1,5-bisphosphate carboxylase-oxygenase. I. Structural, immunochemical and catalytic properties

Some structural, immunochemical and catalytic properties are examined for ribulose 1,5-bisphosphate carboxylase-oxygenase from various cellular organisms including bacteria, cyanobacteria, algae and higher plants. The native enzyme molecular masses and the subunit polypeptide compositions vary according to enzyme sources. The molecular masses of the large and small subunits from different cellular organisms, on the other hand, show a relatively high homology due to their well-conserved primary amino acid sequence, especially that of the large subunit. In higher plants, the native enzyme and the large subunit are recognized by the antibodies raised against either the native or large subunit, whereas the small subunit apparently cross-reacts only with the antibodies directed against itself. A wide diversity exists, however, in the serological response of the native enzyme and its subunits with antibodies directed against the native enzyme or its subunits from different cellular organisms. According to numerous kinetic studies, the carboxylase and oxygenase reactions of the enzyme with ribulose 1,5-bisphosphate and carbon dioxide or oxygen require activation by carbon dioxide and magnesium prior to catalysis with ribulose 1,5-bisphosphate and carbon dioxide or oxygen. The activation and catalysis are also under the regulation of other metal ions and a number of chloroplastic metabolites. Recent double-labeling experiments using radioactive ribulose 1,5-bisphosphate and 14CO2 have elucidated the carboxylase/oxygenase ratios of the enzymes from different organisms. Another approach, i.e., genetic experiments, has also been used to examine the modification of the carboxylase/oxygenase ratio.

The inhibition of ribulose 1,5-bisphosphate carboxylase oxygenase by several 2-carboxyhexitol 1- and 6-phosphates

The condensation of D-fructose 6-phosphate or 1-phosphate with cyanide has been used to synthesize 2-carboxyhexitol 6-phosphates and 1-phosphates. The products have been characterized in terms of their action on ribulose bisphosphate carboxylase/oxygenase. The reaction of D-fructose 6-phosphate with cyanide is four times as fast (at 22°C) at pH 7.5 than at pH 11.5 and the primary products of condensation are more easily isolated by anion exchange chromatography. Two minor chromatographic peaks (I and II) for diastereomeric 2-carboxyhexitol 6-phosphates are isolated in addition to two major peaks, III and IV, which are lactones. The lactones are those of 2-C-carboxy-D-glucitol 6-phosphate (CG6P) in peak III and 2-C-carboxy-D-mannitol 6-phosphate (CM6P) in peak IV, as established after dephosphorylation by the relative rates of oxidation by periodate and by gas chromatographic retention times of the acetates. Analogous methodology has been used to synthesize the diastereomeric 2-carboxy-hexitol 1-phosphates (CG1P and CM1P) and their lactones from D-fructose 1-phosphate. The four carboxylates inhibit ribulose bisphosphate carboxylase/oxygenase from spinach or Pseudomonas oxalaticus in the following decreasing order of potency: CG6P, CM6P, CG1P, CM1P. The inhibition pattern suggests that the binding of the 5-phosphate moiety of the intermediate in the reaction catalyzed by ribulose bisphosphate carboxylase/oxygenase may be stronger by an order of magnitude than the binding of the 1-phosphate group.

Isolation of a stable enzyme.14CO2.Mg2+.carboxyarabinitol bisphosphate complex with ribulosebisphosphate carboxylase from Chromatium vinosum

Higher plant-type ribulosebisphoshate carboxylase from Chromatium vinosum formed a stable, nonexchangeable complex with activator 14CO2 in the presence of Mg2+ and 2-carboxyarabinitol bisphosphate, an analog of the proposed transition-state intermediate. The response of the procaryotic enzyme to this analog was indistinguishable from that of the higher-plant carboxylase, which should permit comparative analysis of the activator site amino acid sequence in the two proteins.

Thermothrix thiopara: Growth and Metabolism of a Newly Isolated Thermophile Capable of Oxidizing Sulfur and Sulfur Compounds

Thermothrix thiopara is isolated from hot sulfur springs. It occurs in situ at a temperature of 72�C, a pH of 7.0, and an HS - concentration of 17.4 μmol/liter (0.8 ppm). The organism was capable of autotrophic growth. Sulfite, sulfur, and polythionates were formed and subsequently degraded to sulfate during growth with thiosulfate as the sole energy source. Thiosulfate was oxidized by the polythionate pathway, and the stoichiometry of growth on thiosulfate was determined. The organism was also capable of heterotrophic growth in amino acids and simple sugars. A source of reduced sulfur (methionine, glutathione) was required for heterotrophic growth. Growth occurred aerobically or anaerobically with nitrate as a terminal oxidant. Both nitrous oxide and dinitrogen were produced. At 73�C the maximum autotrophic growth rate in batch culture using thiosulfate was 0.56 generation per h. Under the same conditions in continuous culture, washout occurred at a dilution rate of 0.3 to 0.4 per h, corresponding to a cellular growth rate of 0.43 to 0.58 generation per h. This was nearly three times the growth rate for Thiobacillus denitrificans. T. thiopara is gram negative. It was also found to be both lysozyme and penicillin susceptible. As a result, this organism cannot be considered an archaebacterium.

Presence of two subunit types in ribulose 1,5-bisphosphate carboxylase from Thiobacillus intermedius

Ribulose bisphosphate carboxylase (EC 4.1.1.39) has been purified to homogeneity from glutamate-CO2-thiosulfate-grown Thiobacillus intermedius by pelleting the protein from the 93,000 X g supernatant fluid followed by ammonium sulfate fractionation and sedimentation into a discontinuous sucrose density gradient. The molecular weight of the native protein approximated that of the higher plant enzyme (550,000) based on its relative electrophoretic mobility in polyacrylamide disc gels compared with that of standards of known molecular weight, including crystalline tobacco ribulose bisphosphate carboxylase. Sodium dodecyl sulfate electrophoresis in 12% polyacrylamide disc gels and Sephadex G-100 chromatography in the presence of sodium dodecyl sulfate indicated that the purified Thiobacillus protein, like the tobacco enzyme, consisted of two types of nonidentical subunits. The molecular weights of the large and small subunits were estimated to be about 55,000 and 13,000, respectively, by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The carboxylase activity of the protein purified from spinach leaves and T. intermedius responded similarly to the effectors reduced nicotinamide adenine dinucleotide phosphate and 6-phosphogluconate. Contrary to a previous report (K. Purohit, B. A. McFadden, and A. L. Cohen, J. Bacteriol. 127:505-515, 1976), these results indicate that ribulose bisphosphate carboxylase purified from Thiobacillus intermedius closely resembles the higher plant enzyme with respect to quaternary structure, molecular weight, and regulatory properties.

Chemoautotrophic growth of hydrogen-uptake-positive strains of Rhizobium japonicum

Recently reported research from this laboratory has demonstrated the autotrophic growth of certain hydrogen-uptake-positive strains of Rhizobium japonicum and defined minimal conditions for such growth. Ribulose 1,5-bisphosphate carboxylase has been detected in autotrophically growing cells, but at low specific activity. Moreover, growth rates were low, and growth ceased at low cell densities. We report here improved autotrophic growth rates of R. japonicum SR through the use of a modified mineral salts/vitamins medium and a programmed increase in oxygen tension as autotrophic growth proceeds. Under these conditions, ribulose, 1,5-biphosphate carboxylase activity increased greater than 10-fold and crude-extract-uptake-hydrogenase activities were from 20 to 47 times those heretofore reported for free-living R. japonicum. It is likely that previous assays for these enzymes were done on preparations of cells in which their synthesis had been partially repressed. The contribution of CO2 fixation to organic carbon accumulation in autotrophic cells was assessed as sufficient to support observed growth. Enzymological determination of the product of carbon fixation has established a stoichiometric ratio of 1.9 mol of 3-phosphoglycerate per mol of CO2 fixed and unequivocally assigns the role of carbon fixation catalysis to ribulose 1,5-bisphosphate carboxylase. Ammonium served best as a nitrogen source, nitrate was less effective, and gaseous nitrogen would not support autotrophic growth. Ecological, evolutionary, and practical considerations of autotrophy in the rhizobia are briefly discussed in the light of our findings.