Further studies on a new pathway of photosynthetic carbon dioxide fixation in sugar-cane and its occurrence in other plant species

1. The pathway of photosynthesis in sugar-cane, which gives most of the radio-activity fixed during short periods in ¹⁴CO₂ in C-4 of oxaloacetate, malate and aspartate, was examined under varied conditions. 2. The pattern of labelling was essentially the same with leaves of different ages and with leaves equilibrated at carbon dioxide concentrations in the range 0–3·8% (v/v) and light-intensities in the range 1400–9000ft.-candles before adding ¹⁴CO₂. 3. Radioactive products were examined after exposing leaves of 33 different plant species to ¹⁴CO₂ for 4sec. under standard conditions. 4. A labelling pattern typical of sugar-cane was found in several species of Gramineae but not in others. Of 16 species from other Families only a species of Cyperaceae contained a large proportion of the fixed radioactivity in oxaloacetate, malate and aspartate.     

Further studies on fixation with osmium tetroxide

Summary The effect of buffered media containing dextran, sucrose and different organic ions, on the volume of blood and ascitescells during fixation with osmium tetroxide has been studied. The findings are in agreement with similar studies ontissue pieces as reported earlier. The presence of osmium tetroxide causes a marked swelling of the cells as estimated by hematocrit techniques. The swelling can be balanced by an appropriate composition of the fixation vehicle, the significance of which is discussed.

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Zusammenfassung Es wurde die Wirkung von Pufferlösungen, die Dextran, Sucrose und verschiedene organische Ionen enthalten, auf das Volumen von Blut- und Asciteszellen während der Fixation mit Osmiumtetroxyd untersucht. Die Ergebnisse stimmen mit ähnlichen Befunden anGewebsstücken, über die früher berichtet wurde, überein. Die Gegenwart von Osmiumtetroxyd verursacht eine bemerkenswerte Zellschwellung, die mittels Hämatokrit-Technik bestimmt wurde. Die Schwellung kann durch eine angepaßte Zusammensetzung verschiedener Fixierungszusätze ausgeglichen werden. Über die Bedeutung dieser Zusätze wird diskutiert.

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With 2 Figures in the Text     

Light-enhanced carbon dioxide fixation in isolated chloroplasts

Preillumination of leaves of spinach, soybean and maize in theabsence of CO₂ greatly enhanced the capacity for fixing CO₂in an immediately following dark period. Lightenhanced darkCO₂-fixation was further observed in isolated chloroplasts ofspinach and soybean. When isolated chloroplasts were illuminated,CO₂-fixing capacity in the subsequent dark period increasedrapidly at first and later more slowly attaining a stationaryvalue in about 20 min. When the light was turned off at thisstage, the capacity decreased very rapidly becoming zero inabout 10 min. The magnitude of the enhanced dark fixation andits decay in the dark were not influenced by the presence orabsence of atmospheric oxygen. In both leaves and isolated chloroplasts,no significant change in oxygen (21%) occurred in distributionpatterns of radioactivity in products fixed by photosynthetic,or light-enhanced, dark, ¹⁴CO₂-fixation. In preilluminated leaves¹⁴C was incorporated into sucrose in the subsequent dark period,indicating that the photosynthetic carbon reduction cycle isoperating in light-enhanced dark fixation in higher plants. ¹Present address: Noda Institute for Scientific Research, Noda,Chiba Prefecture (Received August 10, 1970; )     

Aspects of nitrogen fixation in Chlorobium

Four strains of the green sulfur bacterium Chlorobium were studied in respect to nitrogen nutrition and nitrogen fixation. All strains grew on ammonia, N₂, or glutamine as sole nitrogen sources; certain strains also grew on other amino acids. Acetylene-reducing activity was detectable in all strains grown on N₂ or on amino acids (except for glutamine). In N₂ grown Chlorobium thiosulfatophilum strain 8327 1 mM ammonia served to switch-off nitrogenase activity, but the effect of ammonia was much less dramatic in glutamate or limiting ammonia grown cells. The glutamine synthetase inhibitor methionine sulfoximine inhibited ammonia switch-off in all but one strain. Cell extracts of glutamate grown strain 8327 reduced acetylene and required Mg²⁺ and dithionite, but not Mn²⁺, for activity. Partially purified preparations of Rhodospirillum rubrum nitrogenase reductase (iron protein) activating enzyme slightly stimulated acetylene reduction in extracts of strain 8327, but no evidence for an indigenous Chlorobium activating enzyme was obtained. The results suggest that certain Chlorobium strains are fairly versatile in their nitrogen nutrition and that at least in vivo, nitrogenase activity in green bacteria is controlled by ammonia in a fashion similar to that described in nonsulfur purple bacteria and in Chromatium.Non-common abbreviations MSX Methionine sulfoximine - MOPS 3-(N-morpholino) propane sulfonic acid This paper is dedicated to Professor Norbert Pfennig on the occasion of his 60th birthday     

Autotrophic carbon dioxide fixation inAcidianus brierleyi

The autotrophic CO₂ fixation pathway inAcidianus brierleyi, a facultatively anaerobic thermoacidophilic archaebacterium, was investigated by measuring enzymatic activities from autotrophic, mixotrophic, and heterotrophic cultures. Contrary to the published report that the reductive tricarboxylic acid cycle operates inA. brierleyi, the enzymatic activity of ATP:citrate lyase, the key enzyme of the cycle, was not detected. Instead, activities of acetyl-CoA carboxylase and propionyl-CoA carboxylase, key enzymes of the 3-hydroxypropionate cycle, were detected only whenA. brierleyi was growing autotrophically. We conclude that a modified 3-hydroxypropionate pathway operates inA. brierleyi.Abbreviations TCA tricarboxylic acid - BV Benzyl viologen     

Nitrogen dioxide fixation in bacterial chromatin studies

Eller, Charles (St. John's University, Jamaica, N.Y.), and William H. Beckert. Nitrogen dioxide fixation in bacterial chromatin studies. J. Bacteriol. 90:1710-1712. 1965.-Satisfactory chromatin staining was obtained with two Bacillus species when nitrogen dioxide was used for fixation in conjunction with either the acid Giemsa or Feulgen staining methods. An impression method was employed for the transfer of bacilli to a new environment as well as for smears. Advantages of nitrogen dioxide fixation are discussed.     

新型固碳途径—3-羟基丙酸循环的研究进展

3-羟基丙酸循环是一种存在于嗜热光合绿丝菌中新型的CO2固定途径.此循环的特征代谢中间物为3-羟基丙酸,该化合物可用于合成许多重要的化工产品,具有很高的工业价值.本文介绍了3-羟基丙酸循环固碳途径的发现、反应机理的逐步阐明过程及最新的研究进展,并对其理论意义和在绿色化工中的应用前景进行了探讨.     

Channeling of carbon monoxide during anaerobic carbon dioxide fixation

Carbon monoxide is an intermediate in carbon dioxide fixation by diverse microbes that inhabit anaerobic environments including the human colon. These organisms fix CO(2) by the Wood-Ljungdahl pathway of acetyl-CoA biosynthesis. The bifunctional CO dehydrogenase/acetyl-CoA synthase (CODH/ACS) catalyzes several key steps in this pathway. CO(2) is reduced to CO at a nickel iron-sulfur cluster called cluster C located in the CODH subunit. Then, CO is condensed with a methyl group and coenzyme A at cluster A, another nickel iron-sulfur cluster in the ACS subunit. Spectroscopic studies indicate that clusters A and C are at least 10-15 A apart. To gain a better understanding of how CO production and utilization are coordinated, we have studied an isotopic exchange reaction between labeled CO(2) and the carbonyl group of acetyl-CoA with the CODH/ACS from Clostridium thermoaceticum. When solution CO is provided at saturating levels, only CO(2)-derived CO is incorporated into the carbonyl group of acetyl-CoA. Furthermore, when high levels of hemoglobin or myoglobin are added to remove CO from solution, there is only partial inhibition of the incorporation of CO(2)-derived CO into acetyl-CoA. These results provide strong evidence for the existence of a CO channel between cluster C in the CODH subunit and cluster A in the ACS subunit. The existence of such a channel would tightly couple CO production and utilization and help explain why high levels of this toxic gas do not escape into the environment. Instead, microbes sequester this energy-rich carbon source for metabolic reactions.     

Energetic factors affecting carbon dioxide fixation in isolated chloroplasts

Light- and HCO₃⁻-saturated (10 millimolar) rates of O₂ evolution (120 to 220 micromoles O₂ per milligram chlorophyll per hour), obtained with intact spinach chloroplasts, are decreased up to 3-fold by changes in assay conditions such as omission of catalase from the medium, the use of high (≥1 millimolar) inorganic phosphate, inclusion of NO₂⁻ as an electron acceptor, or bright illumination at low partial pressures of O₂. These inhibitions may be reversed by addition of uncoupling levels of NH₄Cl or of antimycin concentrations that partially block cyclic electron transfer between cytochrome b₆ and cytochrome f. Measurements of the pH gradient across the thylakoid membrane with the fluorescent probe, 9-aminoacridine, indicate that changes in ΔpH are sufficient to account for both the inhibited and restored rates of electron transport. It follows that the rate of HCO₃⁻-saturated photosynthesis may be restricted by a proton gradient back pressure under these conditions.     

Malate synthesis by dark carbon dioxide fixation in leaves

The rates of dark CO₂ fixation and the label distribution in malate following dark ¹⁴CO₂ fixation in a C-4 plant (maize), a C-3 plant (sunflower), and two Crassulacean acid metabolism plants (Bryophyllum calycinum and Kalanchoë diagremontianum leaves and plantlets) are compared. Within the first 30 minutes of dark ¹⁴CO₂ fixation, leaves of maize, B. calycinum, and sunflower, and K. diagremontianum plantlets fix CO₂ at rates of 1.4, 3.4, 0.23, and 1.0 μmoles of CO₂/mg of chlorophyll· hour, respectively. Net CO₂ fixation stops within 3 hours in maize and sunflower, but Crassulaceans continue fixing CO₂ for the duration of the 23-hour experiment.

A bacterial procedure using Lactobacillus plantarum ATCC No. 8014 and one using malic enzyme to remove the β-carboxyl (C₄) from malate are compared. It is reported that highly purified malic enzyme and the bacterial method provide equivalent results. Less purified malic enzyme may overestimate the label in C₄ as much as 15 to 20%.

The contribution of carbon atom 1 of malate is between 18 and 21% of the total carboxyl label after 1 minute of dark CO₂ fixation. Isotopic labeling in the two carboxyls approached unity with time. The rate of increase is greatest in sunflower leaves and Kalanchoë plantlets. In addition, Kalanchoë leaves fix ¹⁴CO₂ more rapidly than Kalanchoë plantlets and the equilibration of the malate carboxyls occurs more slowly. The rates of fixation and the randomization are tissue-specific. The rate of fixation does not correlate with the rate of randomization of isotope in the malate carboxyls.