scholarly journals Quantitative studies on ferredoxin in greening bean leaves

1973 ◽  
Vol 136 (3) ◽  
pp. 697-703 ◽  
Author(s):  
B. G. Haslett ◽  
R. Cammack ◽  
F. R. Whatley
Keyword(s):  
Red Light ◽  
Chlorophyll Synthesis ◽  
Paramagnetic Resonance ◽  
Quantitative Studies ◽  
Low Concentrations ◽  
Electron Paramagnetic ◽  
Linear Manner ◽  
Cytoplasmic Ribosomes ◽  
Mechanism Operative ◽  
Bean Leaves

Two methods of measuring small amounts of the iron–sulphur protein ferredoxin are described. One involves measurements of the signal at g=1.96 produced by reduced ferredoxin in an e.p.r. (electron-paramagnetic-resonance) spectrometer; the other depends on the rate of ferredoxin-dependent electron transport in a chloroplast bioassay measured in an O2 electrode. These methods of measurement were used to examine the development of ferredoxin during the greening of etiolated bean leaves. Ferredoxin is present in low concentrations in the leaves and cotyledons of 14-day-old etiolated beans (Phaseolus vulgaris L. var. Canadian Wonder), and develops in a linear manner with time when the leaves are illuminated. This synthesis appears to be independent of chlorophyll synthesis during the early stages of greening. However, the chlorophyll/ferredoxin ratio reaches a final value of approx. 360 irrespective of the light intensity, indicating the existence of a control mechanism operative in deciding the stoicheiometry of these components in the mature chloroplast. The ferredoxin synthesis appears to be light-dependent, and red light is the most effective in its promotion. The effect of red illumination is not reversed by far-red light, indicating the absence of a phytochrome control of ferredoxin synthesis. From experiments using specific inhibitors of chloroplast protein synthesis, it is concluded that ferredoxin is synthesized on cytoplasmic ribosomes.

scholarly journals The development of plastocyanin in greening bean leaves

1974 ◽  
Vol 144 (3) ◽  
pp. 567-572 ◽  
Author(s):  
B G Haslett ◽  
R Cammack
Keyword(s):  
Spectral Composition ◽  
Assay Method ◽  
Paramagnetic Resonance ◽  
Maximum Value ◽  
Quantitative Extraction ◽  
Etiolated Seedlings ◽  
Lag Period ◽  
Electron Paramagnetic ◽  
Cytoplasmic Ribosomes ◽  
Bean Leaves

The plastocyanin content of etiolated bean leaves (Phaseolus vulgaris L.) was measured, and the development of the protein in response to light was followed. Measurements were made by quantitative extraction of plastocyanin and a sensitive assay with an O2 electrode. The electron-paramagnetic-resonance (e.p.r.) signal of oxidized plastocyanin was used as an independent check on the validity of the assay method, and on the thoroughness of extraction. After an initial lag period, the amount of plastocyanin in greening bean leaves increased to reach a maximum after 50h illumination. The chlorophyll/plastocyanin ratio reached a maximum value of 200 irrespective of the light intensity at which greening was carried out, suggesting that the synthesis of the two components is co-ordinated. Experiments involving treatment of etiolated seedlings with brief periods of light of different spectral composition indicated that phytochrome is involved in plastocyanin synthesis. The lack of inhibition of plastocyanin synthesis by specific inhibitors of chloroplast protein synthesis suggests that the protein is synthesized on cytoplasmic ribosomes. The data are discussed in relation to the development of ferredoxin in greening bean leaves.

scholarly journals Electron-paramagnetic-resonance studies on nitrogenase of Klebsiella pneumoniae. Evidence for acetylene- and ethylene-nitrogenase transient complexes

1978 ◽  
Vol 173 (1) ◽  
pp. 277-290 ◽  
Author(s):  
D J Lowe ◽  
R R Eady ◽  
R N F Thorneley
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Klebsiella Pneumoniae ◽  
Binding Site ◽  
Dissociation Constants ◽  
Paramagnetic Resonance ◽  
Fe Protein ◽  
Low Concentrations ◽  
Direct Binding ◽  
Electron Paramagnetic ◽  
Single Binding Site

Klebsiella pneumoniae nitrogenase exhibited four new electron-paramagnetic-resonance signals during turnover at 10 degrees C, pH7.4, which were assigned to intermediates present in low concentrations in the steady state. 57Fe-substituted Mo–Fe protein showed that they arose from Fe–S clusters in the Mo–Fe protein of nitrogenase. The new signals are designated: Ic, g values at 4.67, 3.37 and approx. 2.0; VI, g values at 2.125, 2.000 and 2.000; VII, g values at 5.7 and 5.4; VIII, g values at 2.092, 1.974 and 1.933. The sharp axial signal VI arises from a Fe4S4 cluster at the −1 oxidation level. This signal was only detected in the presence of ethylene and provides the first evidence of an enzyme–product complex for nitrogenase. [13C]Acetylene and [13C]ethylene provided no evidence for direct binding of this substrate and product to the Fe–S clusters giving rise to these signals. The dependence of signal intensities on acetylene concentration indicated two types of binding site, with apparent dissociation constants K less than 16 micron and K approximately 13mM. A single binding site for ethylene (K=1.5mM) was detected. A scheme is proposed for the mechanism of reduction of acetylene to ethylene and inhibition of this reaction by CO.

scholarly journals Purification and properties of formate dehydrogenase from Pseudomonas aeruginosa. Electron-paramagnetic-resonance studies on the molybdenum centre

1987 ◽  
Vol 243 (1) ◽  
pp. 235-239 ◽  
Author(s):  
P M A Gadsby ◽  
C Greenwood ◽  
A Coddington ◽  
A J Thomson ◽  
C Godfrey
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Electron Paramagnetic Resonance ◽  
Hyperfine Coupling ◽  
Formate Dehydrogenase ◽  
Sodium Dithionite ◽  
Paramagnetic Resonance ◽  
Low Concentrations ◽  
Purification And Properties ◽  
Electron Paramagnetic ◽  
Fold Excess

Formate dehydrogenase from Pseudomonas aeruginosa contains molybdenum, a [4Fe-4S] cluster and cytochrome b. This paper reports the detection of molybdenum as Mo(V) by e.p.r. spectroscopy. In order to generate Mo(V) signals, addition of amounts of excess formate varying between 10- and 50-fold over enzyme, followed by 200-fold excess of sodium dithionite, were used. Two Mo(V) species were observed. One, the major component, has g1 = 2.012, g2 = 1.985 and g3 = 1.968, appeared at low concentrations of formate and increased linearly in intensity with increasing concentrations of formate up to 25-fold excess over the enzyme. At higher formate concentration this signal disappeared. The appearance and disappearance of this Mo(V) signal seems to parallel the state of reduction of the [4Fe-4S] clusters. A second, minor, Mo(V) species with g-values g1 = 1.996, g2 = 1.981 and g3 = 1.941 appears at a constant level during the formate-dithionite titration. No evidence has been obtained for nuclear hyperfine coupling to protons. The major Mo(V) species has unusual e.p.r. signals compared with other molybdenum-containing enzymes, except for that observed in the formate dehydrogenase from Methanobacterium formicicum [Barber, Siegel, Schauer, May & Ferry (1983) J. Biol. Chem. 258, 10839-10845]. The present work suggests that the enzyme is acting as a CO2 reductase, with dithionite as an electron donor to a [4Fe-4S] cluster, which in turn donates electrons to molybdenum, producing a Mo(V) species with CO2 bound to the metal.

scholarly journals Complex-formation between reduced xanthine oxidase and purine substrates demonstrated by electron paramagnetic resonance

1969 ◽  
Vol 114 (4) ◽  
pp. 735-742 ◽  
Author(s):  
Frances M. Pick ◽  
R C Bray
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Xanthine Oxidase ◽  
Active Site ◽  
Paramagnetic Resonance ◽  
Freezing Method ◽  
Low Concentrations ◽  
Appearance Rate ◽  
High Concentrations ◽  
Electron Paramagnetic ◽  
Do So

The origin of the Rapid molybdenum electron-paramagnetic-resonance signals, which are obtained on reducing xanthine oxidase with purine or with xanthine, and whose parameters were measured by Bray & Vänngård (1969), was studied. It is concluded that these signals represent complexes of reduced enzyme with substrate molecules. Xanthine forms one complex at high concentrations and a different one at low concentrations. Purine forms a complex indistinguishable from the low-concentration xanthine complex. There are indications that some other substrates also form complexes, but uric acid, a reaction product, does not appear to do so. The possible significance of the complexes in the catalytic cycle of the enzyme is discussed and it is suggested that they represent substrate molecules bound at the reduced active site, waiting their turn to react there, when the enzyme has been reoxidized. Support for this role for the complexes was deduced from experiments in which frozen samples of enzyme–xanthine mixtures, prepared by the rapid-freezing method, were warmed until the signals began to change. Under these conditions an increase in amplitude of the Very Rapid signal took place. Data bearing on the origin of the Slow molybdenum signal are also discussed. This signal disappears only slowly in the presence of oxygen, and its appearance rate is unaffected by change in the concentration of dithionite. It is concluded that, like other signals from the enzyme, it is due to Mov but that a slow change of ligand takes place before it is seen. The Slow species, like the Rapid, seems capable of forming complexes with purines.

Evolution structurale et fonctionnelle de l'appareil photosynthétique des spores de Funaria hygrometrica et de Bryum capillare au cours de leur germination

1974 ◽  
Vol 52 (5) ◽  
pp. 927-934 ◽  
Author(s):  
D. Chevallier ◽  
F. Nurit
Keyword(s):  
Electron Microscopy ◽  
Electron Paramagnetic Resonance ◽  
Chlorophyll Synthesis ◽  
Paramagnetic Resonance ◽  
Funaria Hygrometrica ◽  
Photosynthetic System ◽  
Inorganic Medium ◽  
Electron Paramagnetic ◽  
Isolated Chloroplasts

The mature spores of Funaria hygrometrica Hedw. contain proplasts that are transformed into chloroplasts in about 24 h, during germination on an inorganic medium in the light. The formation and aggregation of thylakoids are observed by electron microscopy. Studies on chlorophyll synthesis, CO2 fixation during germination, Hill's reaction (2,6-dichlorophenol–indophenol (DP1P)) by isolated chloroplasts, and electron paramagnetic resonance (EPR) signals suggest further correlations between plastid formation and functions.The results on Funaria spores are compared with results on Bryum spores. Mature Bryum capillare Hedw. spores contain chloroplasts that change only slightly during germination. The photosynthetic system of Funaria spores is compared with that of the chloroplasts of Bryum spores.

APHRODISIAN MARBLE FROM THE GÖKTEPE QUARRIES: THE LITTLE BARBARIANS, ROMAN COPIES FROM THE ATTALID DEDICATION IN ATHENS

2012 ◽  
Vol 80 ◽  
pp. 65-87 ◽  
Author(s):  
Donato Attanasio ◽  
Matthias Bruno ◽  
Walter Prochaska ◽  
Alì Bahadir Yavuz
Keyword(s):  
Scientific Data ◽  
Second Century ◽  
Paramagnetic Resonance ◽  
Republican Period ◽  
Fine Grained ◽  
Low Concentrations ◽  
History Of ◽  
High Concentrations ◽  
Marble Quarries ◽  
Electron Paramagnetic

The marble of seven under-lifesize sculptures of barbarians, now in the archaeological museums of Naples, Venice and the Vatican, commonly considered to be Roman copies of the Pergamene Lesser Dedication in Athens, comes from the Göktepe marble quarries near Aphrodisias, as is shown by isotopic, electron paramagnetic resonance, trace analyses, and of petrographic data. Since this marble was used mostly by Aphrodisian artists, this finding confirms, on the basis of scientific data, previous hypotheses on the origin of the sculptors who manufactured the statues. Reliable discrimination from similar fine-grained Asiatic marbles, such as Docimium, is possible primarily on the basis of the composition of the Göktepe marbles, which have unusually low concentrations of manganese and high concentrations of strontium. Present knowledge of the history of the quarries and the distribution of their marbles seems to rule out the possibility that the sculptures date from the late Republican period and supports the opinion, previously proposed on stylistic grounds, that they were manufactured in Rome by Aphrodisian sculptors probably during the first half of the second century ad.

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