Resolution of strawberry virus complexes; the isolation and some properties of virus 3

Aphids ( Capitophorus fragariae Theob.) allowed to feed for several days on a strawberry plant with severe crinkle transmitted two viruses. The isolation and properties of one (virus I) have already been described. The other (virus 3) was separated by transferring the aphids to fresh indicators after 24 hr.
Virus 3 was transmitted by aphids which had been allowed to feed on an infected plant for 6 days or more and persisted in the vector for several days. There was some evidence that the virus has a latent period in the vector. The symptoms produced by virus 3 on Fragaria vesca and Royal Sovereign strawberry are described.
On Royal Sovereign, viruses 1 and 3 together produced symptoms of severe crinkle and viruses z and 3 together produced yellow-edge. A form of severe crinkle is thus shown to be caused by a virus complex which can be resolved by means of the vector, and severe crinkle is shown to be etiologically distinct from mild crinkle.     

Ramifications of a redox switch within a normal cell: its absence in a cancer cell

A previously described model for cellular proliferation, based on the relationship of the cell cycle to redox parameters, is explored here to account for the origin of the cancerous cell and some of its key abnormal characteristics, such as the Warburg effect, apoptosis, aneuploidy, and uncontrolled proliferation. We describe how the redox switch that characterizes normal cells and its absence in cancer cells is responsible for the origin and characteristics of cancer cells. Metabolic and chromosomal changes resulting from the lack of such a redox switch in cancer cells are described. The effects of a well-known carcinogen, cigarette smoking, are also applied to the model. This report emphasizes the role of the threshold intracellular redox potential in regulating cells.     

Oxidation-reduction potentials and spectral properties of some cytochromes from Thiobacillus versutus (A2)

Cytochromes c-550 (acidic), c-550 (basic), c-551 and c-552.5 from Thiobacillus versutus have been highly purified and characterized. Their spectral properties at 77 K are described. Oxidation-reduction titrations of cytochromes c-550 (acidic) and c-550 (basic) showed them to exhibit Nernst values of n = 1, with single redox centres in the cytochromes, and to have midpoint redox potentials at pH 7.0 (E_m,7) of 290 and 260 mV, respectively. Cytochrome c-551 contained two separately titratable redox components, each giving n = 1. The low potential centre (55% of titratable cytochrome) and the high potential centre (45%) had E_m,7 values of ?115 and +240 mV, espectively. Cytochrome c-552.5 also contained at least two redox centres. One (65% of titratable cytochrome) had n = 1 and E_m,7 = 220mV. The remaining 35% appeared to be a low potential component with an E_m,7 possibly as low as ?215 mV. the roles of these cytochromes in respiratory thiosulphate oxidation are discussed.     

Preparation and some properties of 6-substituted flavins as active site probes for flavin enzymes

6-Azidoflavins, 6-thiocyanatoflavins, and 6-mercaptoflavins at the lumiflavin, riboflavin, FMN, and FAD level were prepared from the corresponding 6-aminoflavins and some of their properties investigated. They are bound tightly by apoflavin enzymes which bind either riboflavin, FMN, or FAD. 6-Azidoflavins undergo facile photolysis. One major product was identified as 6-aminoflavin. A further product, which was formed also during acid decomposition of the azide, results from opening of the flavin benzene ring and is proposed to have a lumazine structure. 6-Thiocyanatoflavins are easily converted by dithiothreitol to 6-mercaptoflavins. The latter are stabilized against dimerization in the presence of reducing thiols. 6-Mercaptoflavins have a pK of 5.9, which corresponds to ionization of the 6-SH function. The neutral form is yellow, while the anion is green, due to a long-wavelength band (lambda max approximately 600 nm) extending beyond 700 nm. These properties suggest the use of these 6-substituted flavins for probing the active site of flavin enzymes. Because their reactive substituents are in close proximity to the flavin N(5)-position, these 6-substituted derivatives should also serve as useful probes of the environment around the flavin N(5), a position known to be involved in all flavin-mediated redox processes.     

Distance dependence of interactions between charged centres in proteins with common structural features

Data collected for interactions among redox centres, and interactions between redox centres and acid-base residues in a family of small multihaem cytochromes are analysed. The distance dependent attenuation of the interactions between non-surface charges, for separations that range from 8 to 23 angstroms, can be described by a simple function derived from the Debye-Huckel formalism, fit to 9.5 and 7.6 as values for the relative dielectric constant and Debye length, respectively. However, there is considerable scatter in the data despite the structural similarities among the proteins, which is discussed in the framework of using such simple models in predicting properties of novel proteins.     

EPR determination of interaction redox potentials in a multiheme cytochrome: cytochrome c3 from Desulfovibrio desulfuricans Norway

In cytochromes c3 which contain four hemes per molecule, the redox properties of each heme may depend upon the redox state of the others. This effect can be described in terms of interaction redox potentials between the hemes and must be taken into account in the characterization of the redox properties of the molecule. We present here a method of measurement of these interactions based on the EPR study of the redox equilibria of the protein. The microscopic and macroscopic midpoint potentials and the interaction potentials are deduced from the analysis of the redox titration curves of the intensity and the amplitude of the EPR spectrum. This analysis includes a precise simulation of the spectrum of the protein in the oxidized state in order to determine the relative contribution of each heme to the spectral amplitude. Using our method on cytochrome c3 from D. desulfuricans Norway, we found evidence for the existence of weak interaction potentials between the hemes. The three interaction potentials which have been measured are characterized by absolute values lower than 20 mV in contrast with the values larger than 40-50 mV which have been reported for cytochrome c3 from D. gigas. Simulations of the spectra of samples poised at different potentials indicate a structural modification of the heme with the most negative potential during the first step of reduction. The correspondence between the redox sites as characterized by the EPR potentiometric titration and the hemes in the tridimensional structure is discussed.     

Redox-mediated regulation of connexin proteins; focus on nitric oxide

Connexins are membrane proteins that form hemichannels and gap junction channels at the plasma membrane. Through these channels connexins participate in autocrine and paracrine intercellular communication. Connexin-based channels are tightly regulated by membrane potential, phosphorylation, pH, redox potential, and divalent cations, among others, and the imbalance of this regulation have been linked to many acquired and genetic diseases. Concerning the redox potential regulation, the nitric oxide (NO) has been described as a modulator of the hemichannels and gap junction channels properties. However, how NO regulates these channels is not well understood. In this mini-review, we summarize the current knowledge about the effects of redox potential focused in NO on the trafficking, formation and functional properties of hemichannels and gap junction channels.     

Respiratory Complex I: Structure, Redox Components, and Possible Mechanisms of Energy Transduction

Structural arrangements and properties of redox components of the mitochondrial and bacterial proton-translocating NADH:quinone oxidoreductases are briefly described. A model for the mechanism of proton translocation at first coupling site, which emphasizes participation of specifically Complex I-associated ubisemiquinones, is discussed. An alternative mechanism is proposed where all redox reactions take place in a hydrophilic part of the enzyme and the free energy accumulated as conformational constraint drives the proton pump associated with the hydrophobic polypeptides.     

Beyond paraquats: Dialkyl 3,3′- and 3,4′-bipyridinium amphiphiles as antibacterial agents

Dialkyl 4,4′-bipyridinium compounds, known as ‘paraquats’ (PQs), have a long history of use as herbicides, as redox indicators, and more recently as potent antibacterial agents. However, due to their ability to form reactive oxygen species (ROS) in vivo, PQs are also known to be toxic. We proposed that altering the electrochemical properties of PQ, specifically by preparing isomeric bipyridinium structures with 3,3′- and 3,4′-substitution of the nitrogen heteroatoms on the biaryl core, would maintain antibacterial activity, yet decrease toxicity. We have thus prepared a series of 17 amphiphiles, dubbed ‘metaquat’ (MQ) and ‘parametaquat’ (PMQ), respectively, and investigated their antibacterial and electrochemical properties. Optimal inhibition of bacterial growth was observed in symmetric, biscationic structures; minimum inhibitory concentration (MIC) values measured as low as 0.5 μM against both Gram-positive and Gram-negative bacteria for the compound PMQ-11,11. Electrochemical analysis demonstrated the redox properties of the dialkyl 3,3′- and 3,4′-bipyridinium amphiphiles to be distinct from those of the 4,4′-bipyridinium isomer. Thus MQ and PMQ amphiphiles maintain the strong antibacterial activity of the PQ isomers, but show promise for reduced ROS toxicity.     

Comparison of virulence and activity of some enzymes ofListeria monocytogenes

The virulence of microorganisms and the activity of some enzymes were compared on 17 strains ofListeria monocytogenes, including 5 Patterson's strains, 4 strains maintained for longer periods on nutrient media and 8 strains freshly or recently isolated from animals in our field material. The LD₅₀ and invasivity index were determined as indicators of virulence. The activity of catalase, glucose and lactic acid dehydrogenases and glutamic-oxalo-acetic transaminase were determined quantitatively. Close agreement was found between the values of both indicators of virulence and the activity of catalase. The quantitative assay of catalase and to some extent of some dehydrogenases, as well as glutamic-oxaloacetic transaminase thus represents a simple and satisfactory method of assessing the virulence ofListeria monocytogenes.     

Quantitative analysis of some mechanisms affecting the yield of oxidative phosphorylation: Dependence upon both fluxes and forces

The purpose of this work was to show how the quantitative definition of the different parameters involved in mitochondrial oxidative phosphorylation makes it possible to characterize the mechanisms by which the yield of ATP synthesis is affected. Three different factors have to be considered: (i) the size of the different forces involved (free energy of redox reactions and ATP synthesis, proton electrochemical difference); (ii) the physical properties of the inner mitochondrial membrane in terms of leaks (H⁺ and cations); and finally (iii) the properties of the different proton pumps involved in this system (kinetic properties, regulation, modification of intrinsic stoichiometry).The data presented different situations where one or more of these parameters are affected, leading to a different yield of oxidative phosphorylation.(1) By manipulating the actual flux through each of the respiratory chain units at constant protonmotive force in yeast mitochondria, we show that the ATP/O ratio decreases when the flux increases. Moreover, the highest efficiency was obtained when the respiratory rate was low and almost entirely controlled by the electron supply. (2) By using almitrine in different kinds of mitochondria, we show that this drug leads to a decrease in ATP synthesis efficiency by increasing the H⁺/ATP stoichiometry of ATP synthase (Rigoulet M et al. Biochim Biophys Acta 1018: 91-97, 1990). Since this enzyme is reversible, it was possible to test the effect of this drug on the reverse reaction of the enzyme i.e. extrusion of protons catalyzed by ATP hydrolysis. Hence, we are able to prove that, in this case, the decrease in efficiency of oxidative phosphorylation is due to a change in the mechanistic stoichiometry of this proton pump. To our knowledge, this is the first example of a modification in oxidative phosphorylation yield by a change in mechanistic stoichiometry of one of the proton pumps involved. (3) In a model of polyunsaturated fatty acid deficiency in rat, it was found that non-ohmic proton leak was increased, while ohmic leak was unchanged. Moreover, an increase in redox slipping was also involved, leading to a complex picture. However, the respective role of these two mechanisms may be deduced from their intrinsic properties. For each steady state condition, the quantitative effect of these two mechanisms in the decrease of oxidative phosphorylation efficiency depends on the values of different fluxes or forces involved. (4) Finally the comparison of the thermokinetic data in view of the three dimensional-structure of some pumps (X-ray diffraction) also gives some information concerning the putative mechanism of coupling (i.e. redox loop or proton pump) and their kinetic control versus regulation of mitochondrial oxidative phosphorylation.     

Formation and properties of some wood extractives

Chemical and other data concerning the location and site of formation of heartwood extractives are discussed. The biological conditions in the transition zone adjacent to the heartwood boundary are briefly described and some properties of extractives are given. The classes of polyphenolic compounds found in the wood of Eucalyptus species are listed together with the details of ellagic acid derivatives which are the most common class in this genus.     

Influence of some environmental factors on nitrogen fixation in the rhizosphere of rice

Summary Nitrogen fixers make up a large percentage of the total microflora in the rhizosphere of lowland rice. There are more aerobic nitrogen fixers than there are anaerobic ones. When soil crumbs from the root zone were placed on a nitrogen free agar medium and inoculated at 0, 5, 10, and 21 percent oxygen concentration, colonies of aerobic nitrogen fixers reached their greatest diameter at 5 and 10 percent oxygen. In acetylene reduction assays rice plants grown in paddy fields and in solution culture were tested for the nitrogenase activities of their roots at different oxygen tensions. Nitrogenase activity was highest at 3 percent oxygen, lower at 0 percent, and far lower at 21 percent. When rice was grown in solution culture the redox potential of the nutrient solution strongly influenced nitrogenase activity. With declining redox potential, nitrogenase activity increased to a maximum value but dropped sharply as redox potential further decreased. Ten ppm of combined nitrogen as urea depressed nitrogenase activity on excised roots. Combined nitrogen applied to one part of the root system affected, to some extent, nitrogen fixation on other roots kept in a solution without nitrogen. Nitrogenase activity in a fertility trial with lowland rice, examined at several dates, showed no inhibitory effect of fertilizer nitrogen, however, presumably because the nitrogen concentration in the soil solution rapidly decreased. Instead, an overall stimulating effect of nitrogen dressing was noticeable. Diurnal fluctuations of nitrogenase activity in the rhizosphere, with a peak in the afternoon and low fixation rates after low solar radiation, suggest a photosynthetic effect on nitrogen fixation. re]19751208     

Thiol/disulfide redox states in signaling and sensing

Abstract

Rapid advances in redox systems biology are creating new opportunities to understand complexities of human disease and contributions of environmental exposures. New understanding of thiol–disulfide systems have occurred during the past decade as a consequence of the discoveries that thiol and disulfide systems are maintained in kinetically controlled steady states displaced from thermodynamic equilibrium, that a widely distributed family of NADPH oxidases produces oxidants that function in cell signaling and that a family of peroxiredoxins utilize thioredoxin as a reductant to complement the well-studied glutathione antioxidant system for peroxide elimination and redox regulation. This review focuses on thiol/disulfide redox state in biologic systems and the knowledge base available to support development of integrated redox systems biology models to better understand the function and dysfunction of thiol–disulfide redox systems. In particular, central principles have emerged concerning redox compartmentalization and utility of thiol/disulfide redox measures as indicators of physiologic function. Advances in redox proteomics show that, in addition to functioning in protein active sites and cell signaling, cysteine residues also serve as redox sensors to integrate biologic functions. These advances provide a framework for translation of redox systems biology concepts to practical use in understanding and treating human disease. Biological responses to cadmium, a widespread environmental agent, are used to illustrate the utility of these advances to the understanding of complex pleiotropic toxicities.     

Dichlorophenylurea-insensitive Reduction of Silicomolybdic Acid by Chloroplast Photosystem II

The photoreduction of silicomolybdate and other heteropoly ions by chloroplasts is insensitive to 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea (DCMU). Both water and diphenylcarbazide can be used as electron source for the reduction. Three different assays for silicomolybdate reduction are described including oxygen evolution, formation of a reduced heteropoly blue silicomolybdate, or an indirect assay for reduced silicomolybdate by redox indicators, such as ferricyanide or cytochrome c. The effects of detergents and tris washing are consistent with silicomolybdate reduction through photosystem II before the DCMU site. The effects of orthophenanthroline and bathophenanthroline indicate chelator-sensitive sites in photosystem II before the site of DCMU action.     

Redox interactions in cytochrome c oxidase: from the "neoclassical" toward "modern" models.

Because of recent experimental data on the redox characteristics of cytochrome c oxidase and renewed interest in the role of cooperativity in energy coupling, the question of redox cooperativity in cytochrome c oxidase is reexamined. Extensive redox cooperativity between more than two redox centers, some of which are spectrally invisible, may be expected for this electron transfer coupled proton pump. Such cooperativity, however, cannot be revealed by the traditional potentiometric experiments based on a difference in absorbance between two wavelengths. Multiwavelength analyses utilizing singular value decomposition and second derivatives of absorbance vs. wavelength have revealed a stronger cooperativity than consistent with the "neoclassical" model, which allowed only for weak negative cooperativity between two equipotential one-electron centers. A thermodynamic analysis of redox cooperativity is developed, which includes the possibilities of strong cooperative redox interactions, the involvement of invisible redox centers, conformational changes, and monomer/dimer equilibrations. The experimental observation of an oxidation of one of the cytochromes (a3) with a decrease in applied redox potential is shown to require both strong negative cooperativity and the participation of more than two one-electron centers. A number of "modern" models are developed using the analytical approaches described in this paper. By testing with experimental data, some of these models are falsified, whereas some are retained with suggestions for further testing.     

Chemical properties of catechols and their molecular modes of toxic action in cells, from microorganisms to mammals

Catechols can undergo a variety of chemical reactions. In this review, we particularly focus on complex formations and the redox chemistry of catechols, which play an inportant role in the toxicity of catechols. In the presence of heavy metals, such as iron or copper, stable complexes can be formed. In the presence of oxidizing agents, catechols can be oxidized to semiquinone radicals and in a next step to o‐benzoquinones. Heavy metals may catalyse redox reactions in which catechols are involved. Further chemical properties like the acidity constant and the lipophilicity of different catechols are shortly described as well. As a consequence of the chemical properties and the chemical reactions of catechols, many different reactions can occur with biomolecules such as DNA, proteins and membranes, ultimately leading to non‐repairable damage. Reactions with nucleic acids such as adduct formation and strand breaks are discussed among others. Interactions with proteins causing protein and enzyme inactivation are described. The membrane–catechol interactions discussed here are lipid peroxidation and uncoupling. The deleterious effect of the interactions between catechols and the different biomolecules is discussed in the context of the observed toxicities, caused by catechols.     

Theory of iron-sulfur center N-2 oxidation and reduction by ATP.

The data of Ohnishi (1975) and of Gutman and coworkers on iron-sulfur center N-2 in mitochondria and submitochondrial particles are examined in as much quantitative detail as possible from the standpoint of both chemiosmotic theory and of chemical intermediate (transductase) theory.A method of examination of the behavior of an energy transduction site by plotting its properties as a function of both the high and low redox potentials on either side of the site is described in some detail.That adding ATP causes center N-2 to go oxidized when buffered redox-wise on the low potential side and reduced when buffered on the high potential side can be explained by both chemiosmotic and chemical intermediate theory.Chemiosmotic explanations consistent with the data exclude location of N-2 at the inside of the mitochondrial membrane, but location at the out side or the middle or mobile across the membrane cannot be ruled out by present data.All four abridged transductase models of chemical intermediate theory can be fitted to the data by choice of parameters.That center N-2 is a simple redox couple located at either side of energy transduction site 1 is ruled out.Further experiments needed to clarify present ambiguities are shown to be: (i) Adding ATP while buffering (redox-wise) the NAD⁺-NADH inside whole mitochondria; (ii) mapping the apparent midpoint potential or, alternatively, the redox state as a complete function of the redox potentials on both the high and low sides; (iii) determination of differences that may be caused by sidedness of the preparation (mitochondria or submitochondrial particles); and (iv) determining effects of changing the partitioning of the proton motive force between ΔpH and membrane potential.     

Effect of fluctuating rhizosphere redox potential on carbon assimilation ofSpartina alterniflora

Summary Spartina alterniflora Lois. plants from a Louisiana salt marsh were subjected to fluctuating levels of soil redox potential under controlled environmental conditions. The experiment was designed to examine the changes in carbon assimilation rates in response to the change in rhizosphere sediment redox condition representing a broad range of reduction normally associated with oxygen deficient environments. Variation in sediment redox potential is frequently encountered by this species in its natural environment in Louisiana's Gulf Coast marshes as a result of tidal patterns. Results indicated some adverse effects of extreme anoxic conditions on carbon assimilation ofS. alterniflora, a possible reflection of this species limited ability for maintaining root oxygenation under rapid, intense reduction in soil redox potential. It was also demonstrated that gas exchange limitations may be temporary and apparently may follow by some recovery. Carbon assimilation rates declined 15 to 21% when soil redox level decreased rapidly to below-200 mV which was followed by substantial recovery. A system for accurate control and measurement of rhizosphere redox potential and simultaneous measurement of plant photosynthetic activity is described.     

Comparison of physico-chemical characteristics of four laccases from different basidiomycetes

New strains of basidiomycetes producing extracellular laccases (Trametes ochracea 92-78, and Trametes hirsuta 56) have been found by screening of isolates of Trametes fungi. The laccases from T. hirsuta 56 and T. ochracea 92-78 as well as two laccases from previously found and described strains of basidiomycetes, namely Cerrena maxima and Coriolopsis fulvocinerea, were purified to homogeneity. The standard redox potentials of type 1 copper in the enzymes were determined and found to be 780, 790, 750, and 780 mV, respectively. The spectral and biochemical studies showed that the enzymes had no significant differences between the structures of their active sites (T1, T2, and T3). In spite of this fact, the basic biochemical properties as well as the redox potentials of the T1 sites of the enzymes were found to be different. The molecular weights of the laccases range from 64 to 70 kDa, and their pI values range from 3.5 to 4.7. The pH-optima are in the range 3.5-5.2. The temperature optimum for activity is about 50 degrees C. The thermal stabilities of the enzymes were studied. The catalytic and Michaelis constants for catechol, guaiacol, hydroquinone, sinapinic acid, and K(4)Fe(CN)(6) were determined. Based on these results as well as results obtained by comparing with published properties of several laccases, it could be concluded that T. hirsuta and Cerrena maxima laccases have some superior characteristics such as high stability, high activity, and low carbohydrate content, making them attractive objects for further investigations as well as for application in different areas of biotechnology.