Characterization of inhibitory effects of NH2OH and its N-methyl derivatives on the O2-evolving complex of Photosystem II

Inorganic cofactors (Mn, Ca²⁺ and Cl^-) are essential for oxidation of H₂O to O₂ by Photosystem II. The Mn reductants NH₂OH and its N-methyl derivatives have been employed as probes to further examine the interactions between these species and Mn at the active site of H₂O oxidation. Results of these studies show that the size of a hydroxylamine derivative regulates its ability to inactivate O₂ evolution activity, and that this size-dependent inhibition behavior arises from the protein structure of Photosystem II. A set of anions (Cl^-, F^- and SO₄ ^2-) is able to slow NH₂OH and CH₃NHOH inactivation of intact Photosystem II membranes by exerting a stabilizing influence on the extrinsic 23 and 17 kDa polypeptides. In contrast to this non-specific anion effect, only Cl^- is capable of attenuating CH₃NHOH and (CH₃)₂NOH inhibition in salt-washed preparations lacking the 23 and 17 kDa polypeptides. However, Cl^- fails to protect against NH₂OH inhibition in salt-washed membranes. These results indicate that the attack by NH₂OH and its N-methyl derivatives on Mn occurs at different sites in the O₂-evolving complex. The small reductant NH₂OH acts at a Cl^--insensitive site whereas the inhibitions by CH₃NHOH and (CH₃)₂NOH involve a site that is Cl^- sensitive. These findings are consistent with earlier studies showing that the size of primary amines controls the Cl^- sensitivity of their binding to Mn in the O₂-evolving complex.Abbreviation MES 4-morpholinoethanesulfonic acid - PS II Photosystem II     

Accumulation of technetium by cyanobacteria

Accumulation of pertechnetate ions (⁹⁹TcO₄ ^–) by the cyanobacterial speciesSynechocystis PCC 6803,Synechococcus PCC 6301,Plectonema boryanum,Anabaena variabilis and a redOscillatoria sp. consisted solely of a single rapid energy-independent phase (biosorption); no energy-dependent uptake was detected. Biosorption of TcO₄ ^– was concentration-dependent and could be described by a Freundlich adsorption isotherm for each cyanobacterial species examined. Decreasing pH increased the accumulation of TcO₄ ^– by all the species as did an increase in external NaCl concentration. Accumulation of TcO₄ ^– was also increased inA. variabilis, P. boryanum and the redOscillatoria by an increased external osmotic potential. Concentrations of cations affected TcO₄ ^– accumulation; K⁺ increased accumulation in all the species, Mg²⁺, Ca²⁺, Sr²⁺ and Cs⁺ increased accumulation inSynechococcus PCC 6301 and Ca²⁺ increased accumulation by the redOscillatoria. Some anions decreased TcO₄ ^– accumulation; CO₃ ^2– inA. variabilis and the redOscillatoria, SO₄ ^2– inSynechocystis PCC 6803, and HCO₃ ^– inP. boryanum. The majority of TcO₄ ^– accumulated by all the cyanobacteria was easily desorbed, with no difference in the amounts desorbed between desorption agents of different pH or cation concentration.(*author for correspondence)     

Effect of anions on the cation selectivity of gramicidin-containing liposomes

Summary An osmotic method was used to study the salt permeability induced by gramicidin A in liposomes. Sequences of cation permeation were obtained for iodide, salycilate, acetate und formate salts in liposomes below and above their transition temperature. Salycilate and formate salts, unlike acetate and iodide salts, exhibit the same sequences for cation selectivity in liposomes below and above their transition temperature. These results can be explained by assuming three mechanisms for salt permeation across gramicidin-containing liposomes: (i) the anion moves by the lipid part of the membrane whereas the cation moves by the gramicidin channel, (ii) movement of the undissociated acid species occurs through the lipid part of the membrane followed by cation-proton exchange via the gramicidin channel and (iii) the cation and anion may move simultaneously via the gramicidin channel.When the movement of the anion or undissociated acid across the lipid part of the membrane is not rate limiting the permeation process, the cation selectivity obtained agrees with the cation selectivity of the gramicidin A channel, as determined by others using independent measurements.     

Electrochemical Characteristics of Nitroheterocyclic Compounds of Biological Interest. VIII Stability of Nitro Radical Anions from Cyclic Voltammetric Studies

The stability of the one electron addition product of four biologically important nitroheterocyclic compounds has been examined electrochemically. Using cyclic voltammetry the tendency of the nitro radical anion to undergo disproportionation was studied by two methods of analysis. The first was based on determining the voltammetric time-constant required for half of the reduction product, RNO₂, to react further. The second concerned the minimum volume of dimethylformamide which had to be added to the aqueous electrolytic medium to give a specific cyclic voltammetric response. Both methods were found to compare well with the results obtained for RNO₂T stabilities using a theoretically derived procedure for a second order reaction following a charge-transfer step. The use of these alternative approaches for quantifying the reactivity of reduction products is discussed. The time-constant method in particular may be useful in studying complex reaction pathways.     

Electrochemical Characteristics of Nitro-Heterocyclic Compounds of Biological Interest IV. Lifetime of the Metronidazole Radical Anion

Electrochemical studies on metronidazole using mixed aqueous/dimethylformamide (DMF) solvents have allowed us to generate the one-electron addition product, the nitro radical anion, RNO^?₂. Cyclic volt-ammetric techniques have been employed to study the tendency of RNO^?₂ to undergo further chemical reaction. The return-to-forward peak current ratio. ip/ip_f. was found to increase towards unity with increasing DMF content of the medium, indicating the extended lifetime of RNO^?₂. Second order kinetics for the decay of RNO^?₂ were established at all DMF concentrations examined. Extrapolation has allowed the rate constant and a first half-life of 8.4 × 10⁴dm²/mol-sec and 0.059 seconds respectively, to be determined for the decay of RNO^?₂ in a purely aqueous media. This is impossible by direct electrochemical measurement in water. due to a different reduction mechanism, giving the hydroxylamine derivative in a single 4-electron step. The application of the technique to other nitro-aromatic compounds is discussed.     

Redox Cycling in MCF-7 Human Breast Cancer Cells by Antitumor Agents Based on Mitozantrone

In a series of hydroxyethylaminoalkylaminoanthraquinones (AQ's) based on mitozantrone, 1-AQ (340%) and 1,8-AQ (137%) stimulated basal rate NADPH oxidation (72 + 18pmol min^-lmg S9 protein^-1) whilst 1,4-AQ, 1,5-AQ and mitozantrone had no effect. A similar trend was observed for O_2? generation (measured as nmol acet. cyt c reduction min-¹ mg protein^-1) by these compounds in MCF-7 S9 fraction: 1-AQ (9.5) and 1,8-AQ (7.9), whilst 1,5-AQ, 1,4-AQ and mitozantrone showed no significant effect. All the AQs including mitozantrone were cytotoxic to MCF-7 cells in a dose dependent manner with EC₅₀ values as follows: 1-AQ (0.01 μm) > doxorubicin (0.4μM) > mitozantrone (0.6μM) > 1,8-AQ (2.O μM) > 1,5-AQ (4.0μM) > 1,4-AQ (8,0 μM). Thus the redox active AQs were also the most cytotoxic. Mitozantrone however was not redox active but was more cytotoxic than all but 1-AQ hence it would appear that factors other than free radical generation contribute to the antitumor activity of this group of compounds.     

Fluorine‐Free Noble Salt Anion for High‐Performance All‐Solid‐State Lithium–Sulfur Batteries

Amongst post‐Li‐ion battery technologies, lithium–sulfur (Li–S) batteries have captured an immense interest as one of the most appealing devices from both the industrial and academia sectors. The replacement of conventional liquid electrolytes with solid polymer electrolytes (SPEs) enables not only a safer use of Li metal (Li°) anodes but also a flexible design in the shape of Li–S batteries. However, the practical implementation of SPEs‐based all‐solid‐state Li–S batteries (ASSLSBs) is largely hindered by the shuttling effect of the polysulfide intermediates and the formation of dendritic Li° during the battery operation. Herein, a fluorine‐free noble salt anion, tricyanomethanide [C(CN)₃^?, TCM^?], is proposed as a Li‐ion conducting salt for ASSLSBs. Compared to the widely used perfluorinated anions {e.g., bis(trifluoromethanesulfonyl)imide anion, [N(SO₂CF₃)₂)]^?, TFSI^?}, the LiTCM‐based electrolytes show decent ionic conductivity, good thermal stability, and sufficient anodic stability suiting the cell chemistry of ASSLSBs. In particular, the fluorine‐free solid electrolyte interphase layer originating from the decomposition of LiTCM exhibits a good mechanical integrity and Li‐ion conductivity, which allows the LiTCM‐based Li–S cells to be cycled with good rate capability and Coulombic efficiency. The LiTCM‐based electrolytes are believed to be the most promising candidates for building cost‐effective and high energy density ASSLSBs in the near future.     

Differentiation of the anomeric configuration and ring form of glucosyl-glycolaldehyde anions in the gas phase by mass spectrometry: isomeric discrimination between m/z 221 anions derived from disaccharides and chemical synthesis of m/z 221 standards

Mass spectrometry of disaccharides in the negative-ion mode frequently generates product anions of m/z 221. With glucose-containing disaccharides, dissociation of isolated m/z 221 product ions in a Paul trap yielded mass spectra that easily differentiated between both anomeric configurations and ring forms of the ions. These ions were shown to be glucosyl-glycolaldehydes through chemical synthesis of their standards. By labeling the reducing carbonyl oxygen of disaccharides with 18O to mass discriminate between monosaccharides, it was established that the m/z 221 ions are comprised solely of an intact nonreducing sugar with a two-carbon aglycon derived from the reducing sugar, regardless of the disaccharide linkage position. This enabled the anomeric configuration and ring form of the ion to be assigned and the location of the ion to the nonreducing side of a glycosidic linkage to be ascertained. Detailed studies of experimental factors necessary for reproducibility in a Paul trap demonstrated that the unique dissociation patterns that discriminate between the isomeric m/z 221 ions could be obtained from month-to-month in conjunction with an internal energy-input calibrant ion that ensures reproducible energy deposition into isolated m/z 221 ions. In addition, MS/MS fragmentation patterns of disaccharide m/z 341 anions in a Paul trap enabled linkage positions to be assigned, as has been previously reported with other types of mass spectrometers.     

Effect of Single-Charged Anions of Different Nature on the DNA Molecule Conformation in Water–Salt Solutions

Methods of intrinsic viscosity () and beam flow birefringence were used to study the effects of some single-charged ions (F^–, Cl^–, Br^–, I^–, NO^– ₂, NO^– ₃, ClO^– ₄, SCN^–, CH₃COO^–) on the size and thermodynamic rigidity of a DNA molecule in aqueous solutions of sodium salts in a broad interval of ionic strength when temperature T is changed. It has been shown that the close interactions in a macromolecule and the resulting DNA persistent length a are independent of the type of the salt anion over the whole interval of . On the contrary, the specific volume of the DNA molecule in solution, proportional to the value, is quite sensitive to the anionic composition of the solvent, which is due to the effect of anions and their hydration on the long-range interactions in the macromolecule. The presence of polyatomic and halide anions is manifested differently in the value of DNA. Possible factors responsible for the observed effect and the role of structural alterations of water upon anion hydration are discussed.     

Oxidized LDL through LOX-1 modulates LDL-receptor expression in human coronary artery endothelial cells

Experimental studies have shown that oxidized low-density lipoprotein (ox-LDL) up-regulates its receptor LOX-1. Both ox-LDL and LOX-1 are expressed in atherosclerotic plaques. Native LDL concentrations are elevated in atherosclerosis, suggesting a reduction in LDL-receptors. We hypothesized that ox-LDL via LOX-1 could influence the expression of LDL-receptors. This study was designed to examine the interaction between ox-LDL, LOX-1, and LDL-receptors in human coronary artery endothelial cells (HCAECs). HCAECs were incubated with ox-LDL (10-80 microg/ml) for 3-24h. Ox-LDL decreased the expression of LDL-receptor in a concentration- and time-dependent fashion. The effects of ox-LDL were mediated by its endothelial receptor LOX-1, since pretreatment of HCAECs with a blocking antibody to LOX-1 (JTX92, 10 microg/ml) prevented the effect of ox-LDL on LDL-receptor expression. The role of LOX-1 was further confirmed by the use of an antisense to LOX-1 mRNA, which also blocked the effect of ox-LDL in LDL-receptor expression. In other experiments, ox-LDL as expected induced superoxide anion generation; and pretreatment of HCAECs with the anti-oxidants trolox and alpha-tocopherol (each 10 microM) inhibited the formation of superoxide anions as well as the down-regulation of LDL-receptor in response to ox-LDL. These studies provide the first evidence that ox-LDL via LOX-1 modulates LDL-receptor expression in HCAECs. The generation of free radicals elicited by ox-LDL may be a key step in this process.