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R Cammack

Publications and source records attributed to R Cammack.

At least 109 records · Page 6Linked to original sources
PubMed1982

Iron-sulphur cluster composition and redox properties of two ferredoxins from Desulfovibrio desulfuricans Norway strain.

Two ferredoxins from Desulfovibrio desulfuricans, Norway Strain, were investigated by EPR spectroscopy. Ferredoxin I appears to be a conventional [4Fe-4S]2+;1+ ferredoxin, with a midpoint reduction potential of -374 mV at pH 8. Ferredoxin II when reduced, at first showed a more complex spectrum, indicating an interaction between two [4Fe-4S] clusters, and probably, has two clusters per protein subunit. Upon reductive titration ferredoxin II changed to give a spectrum in which no intercluster interaction was seen. The midpoint potentials of the native and modified ferredoxin at pH 8 were estimated to be -500 and -440 mV, respectively.

Desulfovibrio↗
PubMed1981

Metalloproteins in the evolution of photosynthesis.

Certain metalloproteins are common to all photosynthetic electron transfer chains. These include soluble proteins such as ferredoxins and cytochromes of the c2 type, and membrane-bound components such as cytochrome b, c1 and the Rieske iron-sulphur protein. The sequence of electron transfer Quinone leads to (cyt b, Fe-S, cyt c1) leads to cyt c2 indicates a common precursor to these systems and to the mitochondrial respiratory chain. In cyanobacteria the cytochrome c2 can be interchanged with the copper protein plastocyanin, and furthermore in chloroplasts of higher plants the latter is used exclusively. The ferredoxins in anaerobic photosynthetic bacteria are mostly of the [4Fe-4S] type, probably derived from those of the fermentative bacteria. These could readily be formed in the earliest cells from iron, sulphide and a very simple peptide. In the oxygen-evolving cyanobacteria and the aerobic halobacteria the [2Fe-2S] ferredoxins predominate. The electron transfer chains of the cyanobacteria have been incorporated almost unchanged into the chloroplasts of plants. The electron transfer chains of purple photosynthetic bacteria were probably the precursors of the mitochondrial respiratory chain, as shown by similarities of cytochromes c2 and succinate dehydrogenase. However a different origin of the eukaryotic cytoplasm is indicated by the presence of the copper/zinc superoxide dismutase.

Amino Acid Sequence↗
PubMed1980

Intracellular localization, isolation and characterization of two distinct varieties of superoxide dismutase from Neurospora crassa.

1. Neurospora crassa was found to contain two distinct superoxide dismutases. 2. Most of the activity is associated with the cytosolic fraction and was shown to be the Cu/Zn-containing form of the protein. 3. Mitochondria isolated from Neurospora crassa showed two distinct superoxide dismutases: a cyanide-sensitive Cu/Zn-containing protein and a cyanide-insensitive form which probably contains manganese. 4. Localization experiments, using selective marker enzymes and digitonin fractionation, indicated that the cyanide-sensitive form is localized in the intermembrane space, whereas the cyanide-insensitive form is confined to the mitochondrial matrix space. 5. The cytosolic Cu/Zn-containing superoxide dismutase was isolated in high yields and extensively characterized by using e.p.r. spectroscopy, isoelectric focusing and analytical ultracentrifugation. 6. E.p.r. spectroscopy was used to monitor changes in the copper environment of the native protein after the addition of a number of potential inhibitors and after high-pH treatment. 7. Both of the cyanide-sensitive Cu/Zn-containing enzymes (cytosolic and mitochondrial) appeared to have identical properties which in turn were different from the cyanide-insensitive enzyme. 8. It is probable that the cyanide-insensitive enzyme was not previously detected, owing to its low amount (less than 10% of the total activity), greater lability than the cyanide-sensitive enzyme and the necessity of obtaining a mitochondrial-enriched fraction before its isolation.

Chromatography, DEAE-Cellulose↗
PubMed1980

Antiferromagnetic exchange interaction in the two-iron-two-sulphur ferredoxin from the blue-green alga Spirulina maxima studied with a highly sensitive magnetic balance.

1. A highly sensitive magnetic balance of the Faraday type is described. 2. The magnetic susceptibility of the oxidized and reduced forms of the two-iron-two-sulphur ferredoxin from the blue-green alga Spirulina maxima has been measured over a wide temperature range. 3. The results can be interpreted within a simple model involving antiferromagnetically coupled iron atoms at the active site. The coupling, expressed as --J, is estimated to be 182 +/- 20/cm and 98 +5/-10 /cm for the oxidized and reduced forms, respectively.

Binding Sites↗
PubMed1979

Temperature dependence of the electronic spin-lattice relaxation time in a 2-iron-2-sulfur protein.

The ferredoxins are characterized by a strong temperature dependence of the electronic spin-lattice relaxation time T1. The measurement of this dependence above the liquid nitrogen temperature has been presented in earlier work [1] for the 2-iron-2-sulfur ferredoxin of the blue green alga Spirulina maxima. The different relaxation mechanisms which could be efficient in this range were briefly discussed. In the present paper, we extend the measurement of the temperature dependence of T1 to the low temperature range 1.25 to 30 K. From 1.25 K to 13 K, T1 is obtained by the saturating pulse method, whereas the continuous saturation method is used from 8 K to 30 K. The experimental conditions concerning these methods are discussed. The analysis of the temperature dependence curve over the whole range 1.25 K to 133 K shows clearly that different regions must be distinguished. For each region the possible relaxation processes and the corresponding vibrational modes are discussed.

Cyanobacteria↗
PubMed1979

EPR spectroscopy of the iron-sulphur cluster and sirohaem in the dissimilatory sulphite reductase (desulphoviridin) from Desulphovibrio gigas.

Desulphoviridin in the oxidized state showed EPR signals around g = 6, consistent with the sirohaem being in the high-spin ferric state. This was unreactive with sulphite, sulphide or cyanide; but readily reduced by methyl viologen. When the enzyme was treated with Na2S2O4 the sirohaem was slowly reduced and a spectrum of a reduced iron-sulphur cluster at g = 2.07, 1.93, 1.91 appeared over the course of an hour. An intermediate in this reaction was indicated by a free radical signal which appeared within seconds and then gradually disappeared. On treatment with nitrite and reduced methyl viologen, the enzyme gave a spectrum of a nitroxide derivative similar to that seen with plant nitrite reductase. The midpoint reduction potential of the haem was estimated to be -310 mV or less. The iron-sulphur cluster has a very low potential, being only reduced in the presence of free Na2S2O4 around -560 mV. Desulphoviridin can be classed with sirohaem-containing iron-sulphur proteins.

Binding Sites↗
PubMed1979

EPR spectra of photosystem I and other iron protein components in intact cells of cyanobacteria.

Electron paramagnetic resonance (EPR) spectra were recorded of whole filaments of the cyanobacteria Nostoc muscorum and Anabaena cylindrica. Signals due to manganese were removed by freezing and thawing the cells in EDTA. EPR spectra were assigned on the basis of their g values, linewidths, temperature dependence and response to dithionite and light treatments. The principal components identified were: (i) rhombic Fe3+ (signal at g = 4.3), probably a soluble storage form of iron; (ii) iron-sulfur centers A and B of Photosystem I; (iii) the photochemical electron acceptor 'X' of Photosystem I; this component was also observed for the first time in isolated heterocysts; (iv) soluble ferredoxin which was present at a concentration of 1 molecule per 140 +/- 20 chlorophyll molecules; (v) a membrane-bound iron-sulfur protein (g = 1.92). A signal g = 6 in the oxidized state was probably due to an unidentified heme compound. During deprivation of iron the rhombic Fe3+, centers A, B and X of Photosystem I, and soluble ferredoxin were all observed to decrease.

Cyanobacteria↗
PubMed1979

The iron-sulphur centres of soluble hydrogenase from Alcaligenes eutrophus.

The soluble hydrogenase (hydrogen:NAD+ oxidoreductase (EC 1.12.1.2) from Alcaligenes eutrophus has been purified to homogeneity by an improved procedure, which includes preparative electrophoresis as final step. The specific activity of 57 mumol H2 oxidized/min per mg protein was achieved and the yield of pure enzyme from 200 g cells (wet weight) was about 16 mg/purification. After removal of non-functional iron, analysis of iron and acid-labile sulphur yielded average values of 11.5 and 12.9 atoms/molecule of enzyme, respectively. p-Chloromercuribenzoate was a strong inhibitor of hydrogenase and apparently competed with NAD not with H2. Chelating agents, CO and O2 failed to inhibit enzyme activity. The oxidized hydrogenase showed an EPR spectrum with a small signal at g = 2.02. On reduction the appearance of a high temperature (50--77 K) signal at g = 2.04, 1.95 and a more complex low temperature (less than 30 K) spectrum at g = 2.04, 2.0, 1.95, 1.93, 1.86 was observed. The pronounced temperature dependence and characteristic lineshape of the signals obtained with hydrogenase in 80--85% dimethylsulphoxide demonstrated that iron-sulphur centres of both the [2Fe-2S] and [4Fe-4S] types are present in the enzyme. Quantitation of the EPR signals indicated the existence of two identical centres each of the [4Fe-4S] and of the [2Fe-2S] type. The midpoint redox potentials of the [4Fe-4S] and the [2Fe-2S] centres were determined to be -445 mV and -325 mV, respectively. Spin coupling between two centres, indicated by the split feature of the low temperature spectrum of the native hydrogenase around g = 1.95, 1.93, has been established by power saturation studies. On reduction of the [Fe-4S] centres, the electron spin relaxation rate of the [2Fe-2S] centres was considerably increased. Treatment of hydrogenase with CO caused no change in EPR spectra.

Alcaligenes↗
PubMed1979

Oxidation-reduction reactions of copper-thiolate centres in Cu-thionein.

Cu-thionein from yeast was investigated by EPR spectroscopy to probe the oxidation state of copper, and the effects on it of oxidizing and reducing agents. At pH 0.2 the copper was released, but no EPR signal from Cu(II) was observed, unless air was present. Optical experiments did not detect any disulphide groups which might have been formed during anaerobic release of copper. The mercurial, p-hydroxymercuribenzoate caused the release of EPR-detectable copper only under aerobic conditions, and EDTA caused release of Cu(II) on heating. No reduction of the copper-thiolate units in Cu-thionein by ascorbate was detected. Potentiometric titrations with hexachloroiridate(IV) or hexacyanoferrate(III) produced several different Cu(II) EPR signals at various stages of oxidation. The former oxidizing agent required a lower oxidation-reduction potential (+350 mV) to oxidize the copper, than the latter (+410 mV) and neither titration was fully reversible. The EPR signal from Cu(II) oxidized by hexachloroiridate(IV) resembled that produced by p-hydroxy-mercuribenzoate in air, suggesting that the copper was released from its thiolate ligands. It is concluded that the EPR non-detectable copper in the native protein is Cu(I). Oxidation-reduction of the copper-thiolate clusters of Cu-thionein is proposed to be decisive for controlling storage and transport of cellular copper.

Biological Transport↗
PubMed1978

Electron spin relaxation of iron-sulphur proteins studied by microwave power saturation.

The electron-spin relaxation of iron-sulphur centres in a range of simple proteins (ferredoxin, high-potential iron-sulphur protein and rubredoxin) was investigated by means of the temperature dependence and microwave power saturation of the EPR signal. The proteins containing [2Fe-2S] centres all showed temperature optima higher than those for [4Fe-4S] centres, but the difference between the slowest-relaxing [4Fe-4S] protein (Chromatium high-potential iron-sulphur protein) and the fastest-relaxing [2Fe-2S] protein (Halobacterium halobium ferredoxin) was small. A greater distinction was seen in the power saturation behaviour at low temperature (10--20 K). The behaviour of the signal intensity as a function of microwave power was analyzed in terms of the power for half saturation P 1/2 and the degree of homogeneous/inhomogeneous broadening. The effect of distorting the protein structure by salts, organic solvents and urea was to decrease the electron-spin relaxation rate as shown by a decreased value of P 1/2. The addition of Ni2+ as a paramagnetic perturbing agent caused an increase in the electron-spin relaxation rate of all the proteins, with the exception of adrenal ferredoxin, as shown by an increased P 1/2 and, in a few cases, broadening of the linewidth. Ferricyanide, a commonly used oxidizing agent, has similar effects. These results are discussed in relation to the use of paramagnetic probes to determine whether iron-sulphur centres are near to a membrane surface. Spin-spin interactions between two paramagnetic centres in a protein molecule such as a 2[4Fe-4S] ferredoxin, lead to more rapid electron-spin relaxation. This method was used to detect a spin-spin interaction between molybdenum V and centre Fe-SI in xanthine oxidase.

Chromatium↗
PubMed1978

Oxidation-reduction studies of the Mo-(2Fe-2S) protein from Desulfovibrio gigas.

Potentiometric titration followed by e.p.r. measurements were used to determine the midpoint reduction potentials of the redox centres of a molybdenum-containing iron-sulphur protein previously isolated from Desulfovibrio gigas, a sulphate-reducing bacterium (Moura, Xavier, Bruschi, Le Gall, Hall & Cammack (1976) Biochem. Biophys. Res. Commun. 728 782-789; Moura, Xavier, Bruschi, Le Gall & Cabral (1977) J. Less Common Metals 54, 555-562). The iron-sulphur centres could readily be distinguished into three types by means of g values, temperature effect, oxidation-reduction potential values and reduction rates. The type-I Fe-S centres are observed at 77 K. They show mid-point potential values of -260mV (Fe-S type IA) and -440 mV (Fe-S type IB). Centres of types IA and IB appear to have similar spectra at 77 K and 24 K. The Fe-S type-II centres are only observed below 65 K and have a midpoint potential of -28mV. Long equilibration times (30 min) with dye mediators under reducing conditions were necessary to observe the very slow equilibrating molybdenum signals. The potential values associated with this signal were estimated to be approx. -415 mV for Mo(VI)/Mo(V) and-530mV for Mo(V)/Mo(IV).

Desulfovibrio↗
PubMed1978

Comparative studies on two ferredoxins from the cyanobacterium Nostoc strain MAC.

Two ferredoxins were isolated from the cyanobacterium Nostoc strain MAC grown autotrophically in the light or heterotrophically in the dark. In either case approximately three times as much ferredoxin I as ferredoxin II was obtained. Both ferredoxins had absorption maxima at 276, 282 (shoulder), 330, 423 and 465 nm in the oxidized state, and each possessed a single 2 Fe-2S active centre. Their isoelectric points were approx. 3.2. The midpoint redox potentials of the ferredoxins differed markedly; that of ferredoxin I was --350mV and that of ferredoxin II was --445mV, at pH 8.0. The midpoint potential of ferredoxin II was unusual in being pH dependent. Ferredoxin I was most active in supporting NADP+ photoreduction by chloroplasts, whereas ferredoxin II was somewhat more active in pyruvate decarboxylation by the phosphoroclastic system of Clostridum pasteurianum. Though the molecular weights of the ferredoxins determined by ultracentrifugation were the same within experimetnal error, the amino acid compositions showed marked differences. The N-terminal amino acid sequences of ferredoxins I and II were determined by means of an automatic sequencer. There are 11--12 differences between the sequences of the first 32 residues. It appears that the two ferredoxins have evolved separately to fulfil different roles in the organism.

Amino Acid Sequence↗
PubMed1978

Electron-paramagnetic-resonance studies of the mechanism of leaf nitrite reductase. Signals from the iron-sulphur centre and haem under turnover conditions.

Low-temperature e.p.r. spectra are presented of nitrite reductase purified from leaves of vegetable marrow (Cucurbita pepo). The oxidized enzyme showed a spectrum at g=6.86, 4.98 and 1.95 corresponding to high-spin Fe(3+) in sirohaem, which disappeared slowly on treatment with nitrite. The midpoint potential of the sirohaem was estimated to be -120mV. On reduction with Na(2)S(2)O(4) or Na(2)S(2)O(4)+Methyl Viologen a spectrum at g=2.038, 1.944 and 1.922 was observed, due to a reduced iron-sulphur centre. The midpoint potential of this centre was very low, about -570mV at pH8.1, decreasing with increasing pH. On addition of cyanide, which binds to haem, and Na(2)S(2)O(4), the iron-sulphur centre became further reduced. We think that this is due to an increased midpoint potential of the iron-sulphur centre. Other ligands to haem, such as CO and the reaction product NH(3), had similar but less pronounced effects, and also changed the lineshape of the iron-sulphur signal. Samples were prepared of the enzyme frozen during the reaction with nitrite, Methyl Viologen and Na(2)S(2)O(4) in various proportions. Signals were interpreted as due to the reduced iron-sulphur centre (with slightly different g values), a haem-NO complex and reduced Methyl Viologen. In the presence of an excess of nitrite, the haem-NO spectrum was more intense, whereas in the presence of an excess of Na(2)S(2)O(4) it was weaker, and disappeared at the end of the reaction. A reaction sequence is proposed for the enzyme, in which the haem-NO complex is an intermediate, followed by other e.p.r.-silent states, leading to the production of NH(4) (+).

Electron Spin Resonance Spectroscopy↗
PubMed1978

Damage to mitochondrial electron transport and energy coupling by visible light.

The effect of treating mitochondria with visible light above 400 nm on electron transport and coupled reactions was examined. The temporal sequence of changes was: stimulation of respiration coupled to ATP synthesis, a decline in ATP synthesis, inactivation of respiration, increased ATPase activity and, later, loss of the membrane potential. Loss of respiration was principally due to inactivation of dehydrogenases. Of the components of dehydrogenase systems, flavins and quinones were most susceptible to illumination, the iron-sulfur centers were remarkably resistant to being damaged. Succinate dehydrogenase was inactivated before choline and NADH dehydrogenase. Redox reactions of cytochromes and cytochrome c oxidase activity were unaffected. Inactivation was O2-dependent and prevented by anaerobiosis or the presence of substrates for the dehydrogenases. Light in the range 400-500 nm was most effective and the presence of free flavins greatly enhanced inactivation of all of the above mitochondrial activities. This suggests that visible light mediates a flavin-photosensitized reaction that initiates damage involving participation of an activated species of oxygen in the damage propagation.

Animals↗