Carboxylation Pathway Research Articles

Propionate metabolism in a methanogenic enrichment culture. Direct reductive carboxylation and acetogenesis pathways

Serial dilutions of methanogenic sludges in propionate medium gave a methanogenic non-acetoclastic enrichment degrading 1 mol of propionate to 1.6 mol of acetate and 0.17 mol of methane, with a transient accumulation of butyrate. NMR recordings showed the conversion of [2- 13C]- and [3- 13C]-propionate to [3- 13C]- and [4- 13C]-butyrate, respectively, thus demonstrating a reductive carboxylation of propionate to butyrate. The labelling found in the accumulated acetate and fermentation balances also suggested that reductive carboxylation was the major pathway involved in propionate conversion to acetate.

Propionate metabolism in a methanogenic enrichment culture. Direct reductive carboxylation and acetogenesis pathways

Serial dilutions of methanogenic sludges in propionate medium gave a methanogenic non-acetoclastic enrichment degrading 1 mol of propionate to 1.6 mol of acetate and 0.17 mol of methane, with a transient accumulation of butyrate. NMR recordings showed the conversion of [2-13C]- and [3-13C]-propionate to [3-13C]- and [4-13C]-butyrate, respectively, thus demonstrating a reductive carboxylation of propionate to butyrate. The labelling found in the accumulated acetate and fermentation balances also suggested that reductive carboxylation was the major pathway involved in propionate conversion to acetate.

Covariance of Oxygen and Hydrogen Isotopic Compositions in Plant Water: Species Effects

Leaf water becomes enriched in the heavy isotopes of oxygen and hydrogen during evapotranspiration. The magnitude of the enrichment has been shown to be influenced by temperature and humidity, but the effects of species—specific factors on leaf water enrichment of D and 18O have not been studied for different plants growing together. Accordingly, to learn whether leaf water enrichment patterns and processes for D and 18O are different for individual species growing under the same environmental conditions we tested the proposal that leaf waters in plants with crassulacean acid metabolism (CAM) show higher slopes (m in the leaf water equation °D = m °18O + b) than in C3 plants. We determined the relationships between the stable hydrogen (°D) and oxygen (°18O) isotope ratios of leaf waters collected during the diurnal cycle of evapotranspiration for Yucca schidigera, Ephedra aspera, Agave deserti, Prunus ilicifolia, Yucca whipplei, Heteromeles arbutifolia, Dyckia fosteriana, Simmondsia chinensis, and Encelia farinosa growing at two sites in southern California. Slopes (m in the above leaf water equation) ranged from 1.50 to 3.21, compared to °8 for meteoric water, but differences in slope could not be attributed to carboxylation pathway (CAM vs. C3) nor climate (coastal California vs. Sonoran Desert). Higher slopes were correlated with greater overall ranges of leaf water enrichment of D and 18O. Water in plants with higher slopes also differed most from unaltered meteoric water. Leaf water isotope ratios in plants with lower slopes were better correlated with temperature and humidity. The findings indicate that m in the aforementioned equation is related to the overall residence time for water in the leaf and proportions of water subjected to repeated evapotranspiration enrichments of heavy isotopes.

Anatomy of Succulence and CAM in 15 Species of Senecio

The ability of some species of the genus Senecio to perform Crassulacean acid metabolism (CAM) in plants growing both under controlled conditions and outdoors and the anatomy of their photosynthesizing organs, leaves, and/or stems were investigated. The studied species differed in leaf morphology and in degrees of leaf and stem succulence. Malate accumulation differed with environmental conditions. The carbon isotope ratio δ13C indicated that, in most of the species, the C3 carboxylation pathway was operating, although malate fluctuations indicated that CAM cycling occurred. In some species, carbon isotope ratios ranged between C3 and C4 values, indicating switching of photosynthetic pathways. Only two leafless species that were apparently obligate CAM species had a δ13C typical of plants assimilating CO2 through the phosphoenolpyruvate carboxylase pathway.

Temperature effects on malic-acid efflux from the vacuoles and on the carboxylation pathways in crassulacean-acid-metabolism plants

The studies described in the paper were conducted with tissue slices of Crassulacean acid metabolism (CAM) plants floating in isotonic buffer. In a first series of experiments, temperature effects on the efflux of [(14)C]malate and(14)CO2 were studied. An increase of temperature increased the efflux from the tissue in a non-linear manner. The efflux was markedly influenced also by the temperatures applied during the pretreatment. The rates of label export in response to the temperature and the relative contributions of(14)CO2 and [(14)C]malate to the label export were different in the two studied CAM plants (Kalanchoë daigremontiana, Sempervivum montanum). In further experiments, temperature response of the labelling patterns produced by(14)CO2 fixation and light and darkness were studied. In tissue which had accumulated malate (acidified state) an increase of temperature decreased the rates of dark CO2 fixation whilst the rates of CO2 fixation in light remained largely unaffected. An increase of temperature shifted the labelling patterns from a C4-type (malate being the mainly labelled compound) into a C3-type (label in carbohydrates). No such shift in the labelling patterns could be observed in the tissue which had depleted the previously stored malate (deacidified state). The results indicate that in the acidified tissue the increase of temperature increases the efflux of malate from the vacuole by changing the properties of the tonoplast. It is assumed that the increased export of malic acid lowers the in-vivo activity of phosphoenol pyruvate carboxylase by feedback inhibition.

The role of malate in ammonia assimilation in cotyledons of radish (Raphanus sativus L.)

The relationships between the metabolism of malate, nitrogen assimilation and biosynthesis of amino acids in response to different nitrogen sources (nitrate and ammonium) have been examined in cotyledons of radish (Raphanus sativus L.). Measurements of the activities of some key enzymes and pulse-chase experiments with [(14)C]malate indicate the operation of an anaplerotic pathway for malate, which is involved in the synthesis of glutamine during increased ammonia assimilation. It is most likely that the tricarboxylicacid cycle is supplied with carbon through entry of malate, formed via the phosphoenolpyruvate (PEP)-carboxylation pathway, when 2-oxoglutarate leaves the cycle to serve as precursor for an increased synthesis of glutamine via glutamate. This might occur predominantly in the cytosol via the activity of the glutamine synthetase/glutamate synthase (GS/GOGAT) cycle, the NADH-dependent GOGAT being the rate-limiting activity.

Metabolismus von 14C -Glycin, 14C-Serin und 14C-Homoserin in Synechococcus

Summary Synechococcus (Anacystis nidulans, strain L 1402-1) was grown under normal air conditions (0.03 vol% CO2) and with enriehed CO2 (3.0 vol%) at +35°relative low light (0.6 x 103µ W/cm2).14c incorporation after adding 14C-bicarbonate, 14C-aspartate, 14C-glydne, 14C-homoserine and 14c. serine into several products were studied doing photosynthesis and in the dark. In high CO2 grown cells a very high initial labelling of aspartate and glycine/serine could be observed. Radioactivity of 14C-aspartate was found mainly in glutamate, alanine and threonine. A spartate, isoleucine and succimite were 14C-labelled after exposure to 14C-homoserine during photosynthesis and in the dark. 14C-incorporation into several organic acids (e.g. glyceric acid, malate) and glutamate after feeding 14C-glycine and 14C-serine could be detected during light and dark periods. Results were discussed in respect to the metabolism of amino acids and photosynthetic carboxylation pathways in connection with an interrupted tricarboxylic acid cyde.

Dark Carbon Dioxide Fixation under Aerobic and Anaerobic Conditions in Maize Leaves after Preillumination in the Absence of Oxygen

When dark (14)CO(2) fixation in maize leaves was carried out under anaerobic conditions after preillumination in the absence of O(2), the (14)C incorporation in aspartic acid was transient; its maximum level was very low compared with that of malic acid. The addition of 5% O(2) during the dark fixation period increased the total uptake of (14)CO(2) and the (14)C incorporation into aspartic acid.A study of the intramolecular distribution of radioactivity showed that 71 to 76% of the (14)C was located in the C(4) (beta-carboxyl) of malate and aspartate and the remainder in the C(1). This intramolecular labeling pattern did not change during the 5- to 60-second dark (14)CO(2) fixation period and was scarcely altered by the presence of O(2). Three degradation techniques led to similar data.The significance of these results is discussed taking into account the known possible carboxylation pathways. It is concluded that ribulose 1,5-bisphosphate can be a primary acceptor of CO(2) when maize leaves are preilluminated in the absence of O(2).

Occurrence of C 3 and C 4 Photosynthetic Pathways in North American Grasses

A literature survey was made for the occurrence of C, and C, photosynthetic pathways in the United States Gramineae. Distinctive characteristics of the two photosynthetic pathways are discussed. Leaf anatomy, CO, compensation point, net enhancement of photosynthesis in oxygen-deficient atmosphere, QC discrimination, and initial product labeling were criteria selected to evaluate data for 6 subfamilies including 25 tribes, 138 genera, and 632 species. The Arundinoideae, Bambusoideae, Oryzoideae, and Pooideae (Festucoideae) are composed of species with C, pathways. All tribes within the Eragrostoideae have C, pathways with the exception of Unioleae. Within the Panicoideae, the Andropogoneae and all of the Paniceae, excepting the genera Sacciolepus, Isachne, Oplismenus, Amphicatpum, and Panicum, have C, pathways. The subgenus Dichanthelium within Panicum is C, while the Bupanicum subgenus contains plants with both C, and C, photosynthetic pathways. Plant productivity is dependent on several environmental and biological factors. The most important single factor is photosynthesis. A pathway for carbon dioxide (CO;?) fixation was described by Calvin and Bassham (1962) in which CO2 was incorporated into a 6-carbon compound and rapidly converted to a 3-carbon compound, 3-phosphoglyceric acid (3PGA). Previous to discoveries of Kortschalk et al. (1965) and Hatch and Slack (1966), the Calvin cycle (C,, reductive pentose pathway) was considered the major photosynthetic mechanism for carbon (C) fixation. However, Hatch and Slack (1966) described CO;! fixation in which labeled CO;! was first incorporated in 4-carbon compounds (malic, aspartic , or oxaloacetic acid) prior to transfer to sugars by way of 3-phosphoglycerate. The proposed mechanism involved the operation of two interconnected metabolic cycles. Downton (1970) described carbon fixation into Cd-dicarboxylic acids in mesophyll cells and subsequent incorporation into the Calvin cycle located in the bundle sheath cells. Plants (Cd plants) possessing the 4-carbon pathway (also called Cd, dicarboxylic acid, Kranz type, low CO;! compensation, tropical, Hatch and Slack, or p carboxylation pathway) were of tropical ongm and more efficient. They produced two- to threefold more dry matter than plants possessing the 3-carbon pathway (C, plants), especially in relatively sunny, warm, dry climates (Black 197 1). Distinctive characteristics associated with the Ca pathway prompted intensive research in photosynthetic processes of flowering plants. The most important photosynthetic pathways

Photosynthèse phytoplanctonique: Réponse à un stimulus simple, imitant les variations rapides de la lumière engendrées par les vagues

Experiments were conducted in order to assess the response of marine phytoplankton production to a simplified stimulus modelling rapid light fluctuations induced by sea surface waves. Studies were carried out in the St Lawrence Estuary, during three clear and absolutely calm days. The photosynthesis of artificially incubated samples was generally depressed in fluctuating light, when compared with that in constant light of the same average intensity. There is, however, a daily trend of increased energy utilization in varying light, at saturating intensities, while some unpredictable instances of higher photosynthesis were observed in fluctuating light, especially at low intensities. Results are interpreted in terms of changes in carboxylation pathways, and might be a function of the average fluctuating light intensity and of the sun adaptation by the phytoplankton. It follows that the use of fixed light ‘imitated in situ’ incubators should be viewed with some caution.

CO2-Fixierung isolierter und sick teilender Mesophyllzellen von Pharbitis purpurea

The kinetics of 14 C-incorporation into several products were studied with freshly isolated mesophyll cells from Pharbitis purpurea , with cells in the period of elongation growth and with cells during cell division. The Calvin cycle is the main carboxylation pathway of freshly isolated cells and cells during elongation growth. Furthermore, several amino acids were strongly labelled (glycin, serine, alanine, aspartate, glutamate). 14 C-incorporation into malate and aspartate was interpretated as a carboxylation of phosphoenolpyruvate. The pattern of 14 C-labelled products of mesophyll cells during the stage of cell division differs strongly from the others. In this case malate, citrate/glycerate, aspartate and glutamate were the only compounds labelled. Our findings show that during dedifferentiation of isolated mesophyll cells the carbon metabolism is changing.

Pigmentzusammensetzung und photosynthetische CO2-Fixierung von Cyanidium caldarium und Porphyridium aerugineum

Summary The influence of a change in growth conditions on pigment composition and action spectrum of photosynthesis were studied with Porphyridium aerugineum (strain 1380-2) and Cyanidium caldarium . Under low white light (0.5 • 10 3 erg/cm 2 • sec) the relation between chlorophyll a to phycocyanin was 1: 5,3 in the red alga Porphyridium and 1: 9.2 in Cyanidium. Growing the algae under high light intensity (50.8 • 10 3 erg/cm 2 • sec) reduced the phycocyanin content and changed the relations to 1: 1.6 in Porphyridium and to 1: 6.5 in Cyanidium. In red light of high intensity (20.0 • 10 3 erg/cm 2 sec) practically no changes in the pigment relations were observed. Photosynthetic CO 2 uptake measured with an infrared gas analyzer was relatively low in high white light grown algae. The action spectrum of apparent photosynthesis showed a minimum at 483 nm in all differently grown algae cultures. The highest rate of photosynthesis could be found between 621 and 651 nm. Patterns of 14 C-labelled photosynthetic products were very similar to those of the Calvin cycle which is the main carboxylation pathway in these algae. In Porphyridium cells grown in low white light the effect of blue (432 nm) and red (621 nm) on 14 C-labelled photosynthetic products were investigated. 14 CO 2 incorporation into sugar monophosphates increased under red light. In blue light the percentage distribution of 14 C-labelling into amino acids (aspartate, glutamate, alanine) was higher than under red light. In both algae the behaviour of variations in pigment composition was very similar. Therefore we believe Cyanidium could be a red alga.

Relative Contribution of Ribulose 1,5‐Diphosphate Carboxylase and Phosphoenolpyruvate Carboxylase to CO2 Fixation Activity in Roots of Dark‐grown or Light‐grown Lens culinaris Seedlings

AbstractThe pathway of carbon assimilation in greening roots was compared to the pathway in leaves of Lens culinaris seedlings by means of labelling distribution analysis among the products of 14CO2 fixation in vivo, and in vitro with ribulose 1,5‐diphosphate as the substrate. In green leaves, CO2 fixation via ribulose 1,5‐diphosphate carboxylase predominated largely while, in green roots, this carboxylase activity and the phosphoenolpyruvate carboxylase contributed almost equally to the whole in vivo CO2 fixation. A participation of the activities of both carboxylases according to the double carboxylation pathway in the synthesis of dicarboxylic acids (malate and aspartate) was demonstrated in vitro after 48 h of greening in roots but seemed to be absent in in vivo experiments.

The Pathway of Carbon Dioxide Fixation in Crassulacean Plants

Combined gas chromatography-mass spectrometry of malic acid derivatives has been used to show unequivocally that malic acid, synthesized during active acid accumulation in the dark by Kalanchoë daigremontiana Hammet et Perrier in the presence of (13)CO(2) is produced by a pathway involving a single carboxylation. The significance of the finding that crassulacean malate synthesized in the dark and in the presence of (14)CO(2) often contains 66% of the total carboxyl label in carbon atom 4, which has previously been taken to indicate the operation of a double carboxylation pathway or has been dismissed as an artefact, is discussed.

Wirkung intermittierender Belichtung auf die 14C-markierten Produkte während der Photosynthese-Induktion von Chlorella vulgaris)

Summary CO2 exchange, 14CO2 fixation and radioactive photosynthetic products of Chlorella vulgaris (strain 211-11 f.) were studied during the induction period at + 25° C using intermittent illumination (10 sec light/20 sec dark). The algae were grown under normal air conditions (0,03 vol.-% CO2) at a temperature of +27° C and a light/dark change of 16:8 h. The transients in CO2 uptake in Chlorella measured with an infrared gas analyzer are characterized at +25° C by exhibition of a maximum and a minimum before reaching steady state of photosynthesis. However under condition of intermittent illumination the «primary CO2 uptake« lasted a relatively long time. The autoradiographic studies of the appearance of labelled products during the induction period showed that under intermittent illumination radioactivity was incorporated into malate and aspartate until 1 minute. 3-phosphoglycerate was labelled only after 1 minute and the intermediates of the Calvin cycle after 3 minutes. On the other hand, at normal illumination conditions 3-phosphoglycerate and the sugar phosphates appeared not only earlier, but were also more strongly labelled. The results show that in Chlorella besides the Calvin cycle a carboxylation of phosphoenolpyruvate exists also at higher temperatures. These two carboxylation pathways are involved in the formation of the transients of photosynthetic CO2 uptake in Chlorella. The results are discussed with reference to the preillumination experiments and the C4 pathway in Chlorella.

Comparative studies on the photosynthesis of higher plants

Abstract 1) CO2 compensation points of the plants tested correlate well with the leaf anatomy. Low CO2 compensation plants had well-developed VBS containing large and specialized chloroplasts but no plant with a high CO2 compensation point possessed chloroplasts in the VBS. 2) CO2 Compensation Points Closely Correlated With The Major Carboxylation Pathway In Photosynthesis. Low Compensation Plants Fixed CO2 Via The C-4 Pathway (C-4 Plants) While High Compensation Plants Carried Out CO2 Fixation By The Calvin Cycle (C-3 Plants). 3) Close correlations could be established for the CO2 compensation point, the major carboxylation pathway, and glycolate oxidase activity. Glycolate oxidase activity was much higher in C-3 plants than in C-4 plants. On the other hand, dark respiration in C-4 plants was higher than that in C-3 plants. 4) TCA cycle activity in detached leaves was not inhibited to any large extent by illumination. In C-3 plants, the release of 14CO2 from alanine-1-14C increased with an increase in th...

Einflu� der Temperatur auf die Lichtatmung der Blaualge Anacystis nidulans

CO2 exchange, 14CO2 fixation and 14C-products of Anacystis nidulans (strain L 1402-1) were studied during the induction period at temperatures of +15°C and+35°C. At+15°C the stationary rates of CO2 uptake and respiration were reached directly. At+35°C a maximum of CO2 uptake could be observed at the beginning of the illumination period followed by a lower steady rate of photosynthesis. In the following dark period a CO2 gush appeared at+35°C. The magnitude of the CO2 outburst is relatively independent of the photosyntbetic period. The autoradiographic studies showed that the Calvin cycle is the main carboxylation pathway in Anucystis. At a temperature of +35°C serine was labelled after 20 sec of photosynthesis. At+15°C, on the other hand, a low radio-activity appeared in serine after 5 min of photosynthesis. The results show that photorespiration of Anacystis is stimulated by high temperatures.

A VIRESCENS MUTANT OF PHASEOLUS VULGARIS: PHOTOSYNTHESIS AND METABOLIC CHANGES DURING LEAF DEVELOPMENT

SummaryFixation of 14CO2, photophosphorylation, and protein, lipid and RNA composition have been compared for primary and trifoliate leaves of various ages of control and mutant plants.Except when old, leaves of control plants fix more CO2 than do those of the mutant, but the carboxylation pathways seem similar in the two plants. The level of Fraction I protein and that of ribulose diphosphate carboxylase activity are also similar, but lower in leaves of the mutant. Photophosphorylation per chloroplast mediated by photosystems I and II, tends to be slightly higher in the mutant, despite lower levels of chlorophyll in mutant plastids. Small differences in amount and composition of leaf lipids, but large differences in RNA content were found. Mutant leaves show a higher initial content of cytoplasmic ribosomal RNA than do controls; as leaves age this position is reversed. Chloroplast ribosomal RNA is initially similar, but continued synthesis is greater and more prolonged in the mutant.The significance of these data is discussed in relation to the nature of the mutation.

Carbon dioxide compensation—its relation to photosynthetic carboxylation reactions, systematics of the Gramineae, and leaf anatomy

The carbon dioxide compensation concentration of members of the Gramineae and a few other plants was determined with an infrared CO2 analyzer. These results were then considered in relation to the new photosynthetic carboxylation pathway proposed by Hatch et al., rates of photosynthesis, grass systematics, leaf anatomy, and distribution of starch in the leaf. Plants possessing the new carboxylation pathway had low compensation values whereas those having the Calvin carboxylation reaction had high values. Low compensation plants also had a well-developed parenchyma bundle sheath containing a high concentration of chloroplasts which accumulated large amounts of starch. Little or no starch was present in the mesophyll cells. Cyperus was exceptional in that it also formed appreciable starch in the mesophyll. Those low compensation members of the Gramineae tested belonged either to the chloridoid–eragrostoid or the panicoid lines of evolution. A literature survey indicated that low compensation grasses have photosynthetic rates that are about double those of plants with photorespiration correlated with a temperature optimum for photosynthesis of about 35 °C. Those plants with photorespiration have optima within the range 10–25 °C. Some simple assay procedures proposed on the basis of the above correlations allow rapid determination of the physiological and biochemical status of plants with respect to photosynthesis.

Importance of the isovalerate carboxylation pathway of leucine biosynthesis in the rumen.

Certain anaerobic ruminal bacteria synthesize the leucine carbon skeleton by use of a pathway different from that described in other microorganisms. These organisms carboxylate the intact carbon skeleton of isovalerate, synthesizing leucine-2-C(14) from isovalerate-1-C(14). Strains of Bacteroides ruminicola and Peptostreptococcus elsdenii were like Ruminococcus flavefaciens in that they incorporated appreciable amounts of C(14) from isovalerate-1-C(14) into cellular protein and in that the only labeled amino acid found was leucine. The specific activity of beta-isopropylmalate dehydrogenase in extracts from R. flavefaciens and from the mixed bacterial population from the rumen was very low as compared with the specific activity of this enzyme in extracts from Escherichia coli. This suggests that the pathway of leucine biosynthesis that operates in many aerobic and facultative microorganisms is not the major pathway in rumen bacteria. This was supported by the finding that after fermentation of whole rumen contents with acetate-2-C(14), leucine from the bacterial cells had a specific activity lower than one would expect if acetate was incorporated directly into carbons 1 and 2 of leucine.