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1.
Desulfovibrio baarsii is a sulfate reducing bacterium, which can grown on formate plus sulfate as sole energy source and formate and CO 2 as sole carbon sources. It is shown by 14C labelling studies that more than 60% of the cell carbon is derived from CO 2 and the rest from formate. The cells thus grow autotrophically. Labelling studies with [ 14C]acetate, 14CO and [ 14C]formate indicate that CO 2 fixation does not proceed via the Calvin cycle. The labelling patterns of alanine, aspartate, glutamate, and glucosamine indicate that acetate (or activated acetic acid) is an early intermediate in formate and CO 2 assimilation; the methyl group of acetate is derived from formate, and the carboxyl group from CO 2 via CO; pyruvate is formed from acetyl-CoA by reductive carboxylation. The capacity to synthesize an acetate unit from two C 1-compounds obviously distinguishes D. baarsii from those Desulfovibrio species, which require acetate as a carbon source in addition to CO 2. 相似文献
2.
In the higher plant Vicia faba, anomalous labeling patterns in the organic acids and related amino acids of the tricarboxylic acid cycle which result from photosynthetic 14CO 2 fixation (in conjunction with an enzyme localization pattern unique to plant mitochondria) suggest that the tricarboxylic acid cycle functions primarily as a pathway leading to glutamic acid biosynthesis during autotrophic growth. The distribution of isotope in citrate indicates little recycling of oxaloacetate for the resynthesis of citrate. Rather, malate appears to provide both the C 2 and C 4 fragments for the synthesis of citrate, and [ 3H]formate and 14CO 2-labeling patterns implicate serine as the ultimate C 3 precursor of malate. 相似文献
3.
Syntrophococcus sucromutans is the predominant species capable of O demethylation of methoxylated lignin monoaromatic derivatives in the rumen. The enzymatic characterization of this acetogen indicated that it uses the acetyl coenzyme A (Wood) pathway. Cell extracts possess all the enzymes of the tetrahydrofolate pathway, as well as carbon monoxide dehydrogenase, at levels similar to those of other acetogens using this pathway. However, formate dehydrogenase could not be detected in cell extracts, whether formate or a methoxyaromatic was used as electron acceptor for growth of the cells on cellobiose. Labeled bicarbonate, formate, [1- 14C] pyruvate, and chemically synthesized O-[ methyl- 14C]vanillate were used to further investigate the catabolism of one-carbon (C 1) compounds by using washed-cell preparations. The results were consistent with little or no contribution of formate dehydrogenase and pointed out some unique features. Conversion of formate to CO 2 was detected, but labeled formate predominantly labeled the methyl group of acetate. Labeled CO 2 readily exchanged with the carboxyl group of pyruvate but not with formate, and both labeled CO 2 and pyruvate predominantly labeled the carboxyl group of acetate. No CO 2 was formed from O demethylation of vanillate, and the acetate produced was position labeled in the methyl group. The fermentation pattern and specific activities of products indicated a complete synthesis of acetate from pyruvate and the methoxyl group of vanillate. 相似文献
4.
Metabolic control associated with diauxic growth of Pseudomonas oxalaticus in batch cultures on mixtures of formate and oxalate was investigated by measuring intracellular enzyme and coenzyme concentrations and Q
O
2values during transition experiments from oxalate to formate and vice versa. In transition from oxalate to formate oxalyl-CoA reductase concentration declined after the exhaustion of oxalate and ribulose-1,5-diphosphate carboxylase and 14CO 2 fixation appeared upon addition of formate. In the reciprocal transition, ribulose-1,5-diphosphate carboxylase and 14CO 2 fixation rate declined sharply after formate exhaustion, and oxalyl-CoA reductase appeared only after addition of oxalate. The intracellular NAD and NADP concentrations measured in the same experiments are reported. At substrate exhaustion the proportion of NAD in the reduced form fell from 15–20% to 2%. On addition of formate to an oxalate-starved culture there was an immediate increase in the proportion of NADH to 50%; such an increase was not observed in the reverse experiment.Abbreviations RuDP
ribulose-1,5-diphosphate
- HEPES
2-(N-2 hydroxyethylpiperazin-N-yl) ethane sulphonic acid 相似文献
5.
The formation and metabolism of glycolate in the cyanobacterium Coccochloris peniocystis was investigated and the activities of enzymes of glycolate metabolism assayed. Photosynthetic 14CO 2 incorporation was O 2 insensitive and no labelled glycolate could be detected in cells incubated at 2 and 21% O 2. Under conditions of 100% O 2 glycolate comprised less than 1% of the acid-stable products indicating ribulose 1,5 bisphosphate (RuBP) oxidation only occurs under conditions of extreme O 2 stress. Metabolism of [1- 14C] glycolate indicated that as much as 62% of 14C metabolized was released as 14CO 2 in the dark. Metabolism of labelled glycolate, particularly incorporation of 14C into glycine, was inhibited by the amino-transferase inhibitor amino-oxyacetate. Metabolism of [2- 14C] glycine was not inhibited by the serine hydroxymethyltransferase inhibitor isonicotinic acid hydrazide and little or no labelled serine was detected as a result of 14C-glycolate metabolism. These findings indicate that a significant amount of metabolized glycolate is totally oxidized to CO 2 via formate. The remainder is converted to glycine or metabolized via a glyoxylate cycle. The conversion of glycine to serine contributes little to glycolate metabolism and the absence of hydroxypyruvate reductase confirms that the glycolate pathway is incomplete in this cyanobacterium.Abbreviations AAN
aminoacetonitrile
- AOA
aminooxyacetate
- DIC
dissolved inorganic carbon
- INH
isonicotinic acid hydrazide
- PEP
phosphoenolpyruvate
- PEPcase
phosphoenolpyruvate carboxylase
- PG
phosphoglycolate
- PGA
phosphoglyceric acid
- PGPase
phosphoglycolate phosphatase
- PR
photorespiration
- Rubisco
ribulose-1,5-bisphosphate carboxylase oxygenase
- TCA
trichloroacetic acid
- RuBP
ribulose-1,5-bisphosphate 相似文献
6.
1. The labelling patterns of phosphoglycerate obtained from formate-grown or oxalate-grown Pseudomonas oxalaticus after exposure for 15sec. to [ 14C]formate or [ 14C]oxalate respectively were determined. 2. The phosphoglycerate obtained from the formate-grown cells contained 78% of the radioactivity in the carboxyl group. This is in accord with that predicted for operation of the ribulose diphosphate cycle of carbon dioxide fixation. 3. The labelling pattern of the phosphoglycerate obtained from the oxalate-grown cells approached uniformity, as predicted for the heterotrophic pathway of oxalate assimilation. The departure from complete uniformity may have been due to concurrent 14CO 2 fixation into C 4 dicarboxylic acids. 4. The labelling pattern of phosphoglycerate obtained from cells that had just started to grow on oxalate after adaptation from formate was determined after incubation of the cells for 15sec. with [ 14C]oxalate. This pattern approached uniformity. 5. The pathway of incorporation of 14CO 2 into cells that had just started to grow on oxalate after adaptation from formate, in the presence of either formate or oxalate as energy source, was studied by chromatographic and radio-autographic analysis. 6. It is concluded from the isotopic data that a mixed heterotrophic–autotrophic metabolism, with the former mode predominating, operates in the initial stages of growth on oxalate after adaptation from growth on formate. 相似文献
7.
When glycolate was metabolized in peroxisomes isolated from leaves of spinach beet ( Beta vulgaris L., var. vulgaris) formate was produced. Although the reaction mixture contained glutamate to facilitate conversion of glycolate to glycine, the rate at which H 2O 2 became “available” during the oxidation of [1- 14C]glycolate was sufficient to account for the breakdown of the intermediate [1- 14C]glyoxylate to formate (C 1 unit) and 14CO 2. Under aerobic conditions formate production closely paralleled 14CO 2 release from [1- 14C]glycolate which was optimal between pH 8.0 and pH 9.0 and was increased 3-fold when the temperature was raised from 25 to 35 C, or when the rate of H 2O 2 production was increased artificially by addition of an active preparation of fungal glucose oxidase. 相似文献
8.
In isolated hepatocytes the entry into urea of metabolic 14CO 2; derived from [ 14C] formate is modified by the addition of dichloroacetate and hydroxypyruvate. An explanation is that this results from changes in the cytoplasmic/mitochondrial pH gradient. 14CO 2, derived from [1- 14C]alanine enters into urea more readily than 14CO 2 arising from [1- 14C]glutamate. It is proposed that the difference, which is more than 4-fold, is indicative of a preferred pathway for metabolic CO 2 in liver mitochondria from pyruvate dehydrogenase to carbamoylphosphate synthetase than form oxoglutarate dehydrogenase. Acetazolamide inhibition of carbonic anhydrase is without effect on this observed incorporation into urea. 相似文献
9.
Summary The rate at which H 2O 2 becomes available during glycollate oxidation for further oxidation reactions, especially that of glyoxylate to formate and CO 2, in peroxisomes from spinach-beet ( Beta vulgaris L., var. vulgaris) leaves has been determined by measuring O 2 uptake in the presence and absence of added catalase. The rates observed under air and pure O 2 were sufficient to account for the 14CO 2 released from [l- 14C]glycollate under these conditions; the two reactions showed similar characteristics. In the course of the reaction, a fall in catalase activity was observed concomitant with an increase in 14CO 2 release. There is no evidence that catalase was disproportionately lost from the peroxisomes during isolation, and it is argued that the CO 2 release observed contributes to the photorespiratory CO 2 loss in intact leaves.Abbreviations DCPIP
2,6-dichlorophenolindophenol
- FMN
Flavin mononucleotide 相似文献
10.
Extracts of Pseudomonas C grown on methanol as sole carbon and energy source contain a methanol dehydrogenase activity which can be coupled to phenazine methosulfate. This enzyme catalyzes two reactions namely the conversion of methanol to formaldehyde (phenazine methosulfate coupled) and the oxidation of formaldehyde to formate (2,6-dichloroindophenol-coupled). Activities of glutathione-dependent formaldehyde dehydrogenase (NAD +) and formate dehydrogenase (NAD +) were also detected in the extracts.The addition of d-ribulose 5-phosphate to the reaction mixtures caused a marked increase in the formaldehyde-dependent reduction of NAD + or NADP +. In addition, the oxidation of [ 14C]formaldehyde to CO 2, by extracts of Pseudomonas C, increased when d-ribulose 5-phosphate was present in the assay mixtures.The amount of radioactivity found in CO 2, was 6.8-times higher when extracts of methanol-grown Pseudomona C were incubated for a short period of time with [1- 14C]glucose 6-phosphate than with [U- 14C]glucose 6-phosphate.These data, and the presence of high specific activities of hexulose phosphate synthase, phosphoglucoisomerase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase indicate that in methanol-grown Pseudomonas C, formaldehyde carbon is oxidized to CO 2 both via a cyclic pathway which includes the enzymes mentioned and via formate as an oxidation intermediate, with the former predominant. 相似文献
11.
Benzoyl peroxide in toluene was used to bleach chlorophylls in alcohol extracts from plants fed with 14CO 2 for improved direct measurement by liquid seintillation counting. The 0.5% benzoyl peroxide was better than the saturated solution due to less color quenching. Increased counts occurred with all five common scintillation systems when the leaf extracts were bleached with the 0.5% benzoyl peroxide. However, the relatively colorless root extracts of 14C-labeled photosynthates in alcohol did not require the addition of benzoyl peroxide for decolorization. The addition of 0.5 ml of benzoyl peroxide solution (0.5%) to 0.5 ml of a solution of 10 14C-labeled compounds did not induce the degradation of these compounds. In contrast, sodium hypochlorite at an equal concentration caused considerable losses of radioactivity, with an overall average of 30% reduction of the 10 14C-labeled compounds examined. 相似文献
12.
Accumulation of formate to millimolar levels was observed during the growth of Methanobacterium formicicum species on H 2–CO 2. Hydrogen was also produced during formate metabolism by M. formicicum. The amount of formate accumulated in the medium or the amount H 2 released in gas phase was influenced by the bicarbonate concentration. The formate hydrogenlyase system was constitutive but regulated by formate. When methanogenesis was inhibited by addition of 2-bromoethane sulfonate, M. formicicum synthesized formate from H 2 plus HCO
inf3
sup-
or produced H 2 from formate to a steady-state level at which point the Gibbs free energy (G) available for formate synthesis or H 2 production was approximately -2 to -3 kJ/reaction. Formate conversion to methane was inhibited in the presence of high H 2 pressure. The relative rates of conversion of formate and H 2 were apparently controlled by the G available for formate synthesis, hydrogen production, methane production from formate and methane production from H 2. Results from 14C-tracer tests indicated that a rapid isotopic exchange between HCOO - and HCO
inf3
sup-
occurred during the growth of M. formicicum on H 2–CO 2. Data from metabolism of 14C-labelled formate to methane suggested that formate was initially split to H 2 and HCO
inf3
sup-
and then subsequently converted to methane. When molybdate was replaced with tungstate in the growth media, the growth of M. formicicum strain MF on H 2–CO 2 was inhibited although production of methane was not Formate synthesis from H 2 was also inhibited. 相似文献
13.
The carbon and electron flow pathways and the bacterial populations responsible for transformation of H 2-CO 2, formate, methanol, methylamine, acetate, glycine, ethanol, and lactate were examined in sediments collected from Knaack Lake, Wis. The sediments were 60% organic matter (pH 6.2) and did not display detectable sulfate-reducing activity, but they contained the following average concentration (in micromoles per liter of sediment) of metabolites and end products: sulfide, 10; methane, 1,540; CO 2, 3,950; formate, 25; acetate, 157; ethanol, 174; and lactate, 138. Methane was produced predominately from acetate, and only 4% of the total CH 4 was derived from CO 2. Methanogenesis was limited by low environmental temperature and sulfide levels and more importantly by low pH. Increasing in vitro pH to neutral values enhanced total methane production rates and the percentage of CO 2 transformed to methane but did not alter the amount of 14CO 2 produced from [2- 14C]acetate (~24%). Analysis of both carbon transformation parameters with 14C-labeled tracers and bacterial trophic group enumerations indicated that methanogenesis from acetate and both heterolactic- and acetic acid-producing fermentations were important to the anaerobic digestion process. 相似文献
14.
The rates, products, and controls of the metabolism of fermentation intermediates in the sediments of a eutrophic lake were examined. 14C-fatty acids were directly injected into sediment subcores for turnover rate measurements. The highest rates of acetate turnover were in surface sediments (0- to 2-cm depth). Methane was the dominant product of acetate metabolism at all depths. Simultaneous measurements of acetate, propionate, and lactate turnover in surface sediments gave turnover rates of 159, 20, and 3 μM/h, respectively. [2- 14C]propionate and [ U- 14C]lactate were metabolized to [ 14C]acetate, 14CO 2, and 14CH 4. [ 14C]formate was completely converted to 14CO 2 in less than 1 min. Inhibition of methanogenesis with chloroform resulted in an immediate accumulation of volatile fatty acids and hydrogen. Hydrogen inhibited the metabolism of C 3-C 5 volatile fatty acids. The rates of fatty acid production were estimated from the rates of fatty acid accumulation in the presence of chloroform or hydrogen. The mean molar rates of production were acetate, 82%; propionate, 13%; butyrates, 2%; and valerates, 3%. A working model for carbon and electron flow is presented which illustrates that fermentation and methanogenesis are the predominate steps in carbon flow and that there is a close interaction between fermentative bacteria, acetogenic hydrogen-producing bacteria, and methanogens. 相似文献
15.
Growth of Chlorobium vibrioforme f. thiosulfatophilum NCIB 8327 could be monitored by measurement of turbidity (E 600); absorbance at 745 and 665 nm; increase in methanol-extractable pigment (E 660); fixation of 14CO 2; and titration of thiosulphate and sulphide in the medium. Growth could be inhibited by formate, methionine, tryptophan, tyrosine, threonine, serine and glycine, but not by 14 other amino acids, shikimic acid, some alcohols, sugars or acetate. Inhibition could some-times be relieved by the presence of other amino acids. This was probably partly due to restoration of normal internal amino acid requirements by “feeding”, and partly because uptake of amino acids appeared to show some competition for two or more low specificity uptake systems. Numerous 14C-labelled amino acids, formate and glucose were shown to be photoassimilated by Chlorobium, and the labelling patterns obtained provided information on its pathways of intermediary biosynthesis. Growth inhibition by threonine could be related to the probable presence of a normal branched pathway for the synthesis of the aspartate family of amino acids, with an aspartokinase enzyme subject to strong inhibition by threonine and lysine, separately and in combination. 相似文献
16.
The flow of glyoxylate derived from glycolate into various metabolic routes in the peroxisomes during photorespiration was assessed. Isolated spinach leaf peroxisomes were fed [ 14C] glycolate in the absence or presence of exogenous glutamate, and the formation of radioactive glyoxylate, CO 2, glycine, oxalate, and formate was monitored at time intervals. In the absence of glutamate, 80% of the glycolate was consumed within 2 hours and concomitantly glyoxylate accumulated; CO 2, oxalate, and formate each accounted for less than 5% of the consumed glycolate. In the presence of equal concentration of glutamate, glycolate was metabolized at a similar rate, and glycine together with some glyoxylate accumulated; CO 2, oxalate, and formate each accounted for an even lesser percentage of the consumed glycolate. CO 2 and oxalate were not produced in significant amounts even in the absence of glutamate, unless glycolate had been consumed completely and glyoxylate had accumulated for a prolonged period. These in vitro findings are discussed in relation to the extent of CO 2 and oxalate generated in leaf peroxisomes during photorespiration. 相似文献
17.
Z‐scheme‐inspired tandem photoelectrochemical (PEC) cells have received attention as a sustainable platform for solar‐driven CO 2 reduction. Here, continuously 3D‐structured, electrically conductive titanium nitride nanoshells (3D TiN) for biocatalytic CO 2‐to‐formate conversion in a bias‐free tandem PEC system are reported. The 3D TiN exhibits a periodically porous network with high porosity (92.1%) and conductivity (6.72 × 10 4 S m ?1), which allows for high enzyme loading and direct electron transfer (DET) to the immobilized enzyme. It is found that the W‐containing formate dehydrogenase from Clostridium ljungdahlii (ClFDH) on the 3D TiN nanoshell is electrically activated through DET for CO 2 reduction. At a low overpotential of 40 mV, the 3D TiN‐ClFDH stably converts CO 2 to formate at a rate of 0.34 µmol h ?1 cm ?2 and a faradaic efficiency (FE) of 93.5%. Compared to a flat TiN‐ClFDH, the 3D TiN‐ClFDH shows a 58 times higher formate production rate (1.74 µmol h ?1 cm ?2) at 240 mV of overpotential. Lastly, a bias‐free biocatalytic tandem PEC cell that converted CO 2 to formate at an average rate of 0.78 µmol h ?1 and an FE of 77.3% only using solar energy and water is successfully assembled. 相似文献
18.
High concentrations of both bicarbonate and formate inhibit photosynthetic O 2 evolution at pH 8.0. At this pH, only 2.4% of the total dissolved carbon dioxide exists as CO 2. At pH 7.3, where 11% of the total dissolved carbon dioxide exists as CO 2, HCO 3− no longer inhibits. While formate still inhibits O 2 evolution at pH 7.3, its effect can be partially overcome if CO 2 is also present. The rate of binding of added 14C-labeled inorganic carbon is nearly 10-fold more rapid when the internal pH of thylakoid membranes is at 6.0 than when it is at 7.8. These observations suggest that CO 2, not HCO 3−, is initially bound to the photosystem II reaction center and that the location of the binding site is on the inside thylakoid surface. However, additional data presented here suggest that, after binding, CO 2 is hydrated to HCO 3− + H + in a pH-dependent reaction. Two possible explanations of the “bicarbonate effect” are presented. 相似文献
19.
Large quantities of CO 2 are released within many photosynthesizing tissues in the light by the process of photorespiration. This CO 2 arises largely from the carboxylcarbon atom of glycolate, which is synthesized in chloroplasts during photosynthesis. Glyoxylate is then produced by the glycolate oxidase reaction. The glyoxylate may be directly decarboxylated to CO 2, but some investigators believe the glyoxylate must first be converted to glycine before CO 2 is released during photorespiration. Spinach chloroplasts with their envelope membranes removed in dilute buffer solution have now been shown to carry out the oxidative decarboxylation of [1- 14C]glyoxylate, in the presence of light and manganous ions in an atmosphere containing oxygen, to yield 1 mole each of 14CO 2 and formate. Rates of enzymatic decarboxylation exceeding 50 μmoles of 14CO 2 mg chlorophyll −1 hr −1 were obtained at pH 7.6; hydrogen peroxide is probably the oxidant in the reaction. Heated chloroplasts are inactive under the standard conditions and there is an almost absolute requirement for each of the components listed above. Conditions for some other nonenzymatic decarboxylations of glyoxylate have also been described. [1- 14C]Glycine is decarboxylated by the enzymatic system at only 1% of the rate of [1- 14C]glyoxylate. Maize chloroplast preparations are much less active than spinach chloroplasts. The high rates of CO 2 produced by the spinach system directly from glyoxylate, as well as the need for light and oxygen, suggest that this reaction functions in photorespiration, and that CO 2 arises during photorespiration without glycine as a mandatory intermediate. 相似文献
20.
Experiments were designed to determine the significance of dark CO 2 fixation in excised maize roots, carrot slices and excised tomato roots grown in tissue culture. Bicarbonate- 14C was used to determine the pathway and amounts of CO 2 fixation, while leucine- 14C was used to estimate protein synthesis in tissues aerated with various levels of CO 2. Organic acids were labeled from bicarbonate-14C, with malate being the major labeled acid. Only glutamate and aspartate were labeled in the amino acid fraction and these 2 amino acids comprised over 90% of the 14C label in the ethanol-water insoluble residue. Studies with leucine-14C as an indicator of protein synthesis in carrot slices and tomato roots showed that those tissues aerated with air incorporated 33% more leucine-14C into protein than those aerated with CO2-free air. Growth of excised tomato roots aerated with air was 50% more than growth of tissue aerated with CO2-free air. These studies are consistent with the suggestion that dark fixation of CO2 is involved in the growth of plant tissues. 相似文献
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