The formation and biotransformation of cysteine conjugates of halogenated ethylenes by rabbit renal tubules

The nephrotoxicity of chlorotrifluoroethylene (CTFE) was examined using isolated rabbit renal tubules suspensions. Exposure of the tubules to CTFE resulted in consumption of CTFE, formation of a glutathione conjugate and inhibition of active organic acid transport. Synthetic cysteine, N-acetylcysteine or glutathione conjugates of CTFE inhibited transport indicating S-conjugation as a possible toxic pathway. 1,2-dichlorovinyl glutathione (DCVG), a model synthetic glutathione conjugate, was used to examine the degradation and toxicity of these conjugates. DCVG inhibited rabbit renal tubule transport in vivo and in vitro. The DCVG was found to be degraded with the evolution of glutamine and glycine to produce the ultimate nephrotoxicant, dichlorovinyl cysteine. Dichlorovinyl cysteine is then bioactivated with the release of ammonia. This sequential degradation explains the latency of DCVG-induced renal transport inhibition relative to dichlorovinyl cysteine. It is now evident that certain halogenated ethylenes are capable of being biotransformed to glutathione conjugates in the kidney with their subsequent hydrolysis to nephrotoxic cysteine conjugates.     

Thermoluminescence studies of zinc borate (ZnB2O4) phosphor doped with rare earths for dosimetric aspects

A series of ZnB₂O₄ phosphors doped with different concentrations of Eu and Dy (0.05 0.1, 0.2, 0.5, 1.0 mol%) and co-doped with Ce (1, 2, 5, 7, 10 mol%) respectively was prepared via the solid-state reaction technique and the thermoluminescence (TL) behaviour of gamma ray-irradiated samples was studied. The synthesized samples were irradiated with γ-rays for the dose range 0.03–1.20 kGy. The TL intensity variations with dose, dopant concentration, and the effect of co-doping were studied. The TL response curves for ZnB₂O₄:Eu³⁺ and ZnB₂O₄:Dy³⁺, ZnB₂O₄:Eu³,Ce³⁺ and ZnB₂O₄:Dy³⁺,Ce³⁺ phosphor were observed. It was revealed that ZnB₂O₄:Eu³⁺ showed a linear TL behaviour for the dose 0.03–1.20 kGy and ZnB₂O₄:Dy³⁺ showed linearity for the gamma dose range 0.03–0.10 kGy. Furthermore, fading for all the samples was observed to be less than 10% for a storage period of 30 days. In addition to this, the trapping parameters, especially activation energies were evaluated using the Ilich method and the initial rise method. The activation energy values obtained from both methods were in complete agreement with each other.     

A partial sequence of ionic changes associated with the acrosome reaction of Strongylocentrotus purpuratus

Relationships among several of the ion movements associated with the acrosome reaction of S. purpuratus were investigated. Egg jelly initiates ⁴⁵Ca²⁺ and ²²Na⁺ uptake, and K⁺ and H⁺ efflux. H⁺ efflux and ²²Na⁺ uptake occur with approximately equivalent stoichiometries as rapidly as the appearance of acrosomal rods, perhaps reflecting a linked process. Most K⁺ loss, as measured either by ⁴²K⁺ efflux or K⁺-ion-selective electrodes, occurs after the acrosome reaction is complete. Since an elevation of seawater K⁺ (from 10 to 15 mM) or the addition of 0.5 mM tetraethylammonium (TEA), an inhibitor of K⁺ channels, inhibits the acrosome reaction half-maximally, K⁺ movements or alterations of K⁺-dependent membrane potentials may regulate the triggering by jelly. Most, but not all, of the ⁴⁵Ca²⁺ influx is inhibited with a mixture of 10 μM FCCP, 1 mM CN^?, and 2 μg/ml oligomycin, suggesting that the mitochondria store most of the Ca²⁺. The extracellular Na⁺ concentration affects Ca²⁺ fluxes: sperm placed into 5 mM Na⁺ seawater have enhanced ⁴⁵Ca²⁺ uptake, but do not undergo the acrosome reaction, unless 30 mM Na⁺ is also added. Low Na⁺ concentrations lead to spontaneous triggering, by allowing for both Ca²⁺ influx and Na⁺-dependent H⁺ efflux. At least one early Ca²⁺ requirement precedes the Na⁺ and H⁺ movements, as inferred from attempts at reversing the inhibitors of jelly induction of the acrosome reaction. When sperm are incubated with jelly in the absence of Ca²⁺, then washed and incubated with jelly in the presence of Ca²⁺, the acrosome reaction is triggered only upon the second incubation. However, when sperm are mixed with jelly in the presence of the other inhibitors (verapamil, TEA, 5 mM Na⁺ seawater, low pH, or elevated K⁺), they are altered so that even upon subsequent washing, jelly-mediated triggering is no longer possible. This suggests the existence of an intermediate state in the reaction pathway, that follows an event for which Ca²⁺ is required, but that precedes the Na⁺ and H⁺ movements, which are inhibited by all inhibitors of the acrosome reaction. These data are used to develop a partial sequence of ionic changes associated with the triggering mechanism.     

Molecular Dynamics Study of BaB2O4 in Crystalline and Molten States

Abstract

Structural aspects of BaB₂O₄ liquids have been investigated by the molecular dynamics simulation including the determination on the parameters of the interatomic potential applicable to BaB₂O₄ in both crystalline and molten states. The structure and physical properties of BaB₂O₄ crystals were successfully reproduced by the MD simulation for both α and β phases. The simulated interference function in the liquid state was also in good agreement with the experimental one. Several interesting features on the relaxation phenomena just after melting were reproduced by the simulation that the structure factors of simulated liquid maintain the characteristic features of the original crystal structure for more than 40ps after melting, and the variation of the number of rings formed by B-O bondings was found to increase after melting.     

Enzymatic synthesis of dTDP-4-amino-4,6-dideoxy-D-glucose using GerB (dTDP-4-keto-6-deoxy-D-glucose aminotransferase)

Over-expressed GerB (dTDP-4-keto-6-deoxy-d-glucose aminotransferase) of Streptomyces sp. GERI-155 was used in the enzymatic synthesis of dTDP-4-amino-4,6-dideoxy-D-glucose (2) from dTDP-4-keto-6-deoxy-D-glucose (1). [Carbohydrate structure: see text]. Five enzymes including dTMP kinase (TMK), acetate kinase (ACK), dTDP-glucose synthase (TGS), dTDP-glucose 4,6-dehydratase (DH), and dTDP-4-keto-6-deoxy-d-glucose aminotransferase (GerB) were used to synthesize 2 on a large scale from glucose-1-phosphate and TMP. A conversion yield of up to 57% was obtained by HPLC peak integration given a reaction time of 270min. After purification by two successive preparative HPLC systems, the final product was identified by HPLC and then analyzed by (1)H, (13)C, (1)H-(1)H COSY NMR spectrometry.     

Affinity and location of an internal K+ ion binding site in shaker K channels

We have examined the interaction between TEA and K+ ions in the pore of Shaker potassium channels. We found that the ability of external TEA to antagonize block of Shaker channels by internal TEA depended on internal K+ ions. In contrast, this antagonism was independent of external K+ concentrations between 0.2 and 40 mM. The external TEA antagonism of internal TEA block increased linearly with the concentration of internal K+ ions. In addition, block by external TEA was significantly enhanced by increases in the internal K+ concentration. These results suggested that external TEA ions do not directly antagonize internal TEA, but rather promote increased occupancy of an internal K+ site by inhibiting the emptying of that site to the external side of the pore. We found this mechanism to be quantitatively consistent with the results and revealed an intrinsic affinity of the site for K+ ions near 65 mM located approximately 7% into the membrane electric field from the internal end of the pore. We also found that the voltage dependence of block by internal TEA was influenced by internal K+ ions. The TEA site (at 0 internal K+) appeared to sense approximately 5% of the field from the internal end of the pore (essentially colocalized with the internal K+ site). These results lead to a refined picture of the number and location of ion binding sites at the inner end of the pore in Shaker K channels.     

Organopalladium(IV) and platinum(IV) complexes containing the bis(pyrazol-1-yl)borate ligand. Structures of PtMe3{(pz)2BH2}(py) (py=pyridine) and Pt(mq)Me2{(pz)2BH2} (mq=8-methylquinolinyl) and detection of a neutral organopalladium(IV) phosphine complex

Neutral palladium(IV) complexes containing the bis(pyrazol-1-yl)borate ligand, PdMe₃{(pz)₂BH₂}(L) [L=py-d₅ (4), PMe₂Ph (6)], are generated in solution by oxidative addition of iodomethane to [PdMe₂{(pz)₂BH₂}]⁻ at −70 °C followed by addition of L; the Pd(IV) complexes reductively eliminate ethane above 0 °C. Stable Pt(IV) analogues of 4 and 6 have been isolated, and comparison of NMR spectra for Pd(IV) and Pt(IV) species support structural assignments for the unstable Pd(IV) complexes. The complex PtMe₃{(pz)₂BH₂}(py) (1a) has been characterised by X-ray diffraction, together with Pt(mq)Me₂{(pz)₂BH₂} (2) (mq=8-methylquinolinyl); both complexes show a fac-PtC₃ configuration for Pt(IV), and for 2 the PtN distances are ∼0.03 Å shorter than in the isostructural Pd(IV) complex.     

Coupled Ion Movement Underlies Rectification in an Inward-Rectifier K+ Channel

We studied block of the internal pore of the ROMK1 inward-rectifier K⁺ channel by Mg²⁺ and five quaternary ammoniums (tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, and tetrapentylammonium). The apparent affinity of these blockers varied as a function of membrane voltage. As a consequence, the channel conducted K⁺ current more efficiently in the inward than the outward direction; i.e., inward rectification. Although the size of some monovalent quaternary ammoniums is rather large, the zδ values (which measure voltage dependence of their binding to the pore) were near unity in symmetric 100 mM K⁺. Furthermore, we observed that not only the apparent affinities of the blockers themselves, but also their dependence on membrane voltage (or zδ), varied as a function of the concentration of extracellular K⁺. These results suggest that there is energetic coupling between the binding of blocking and permeating (K⁺) ions, and that the voltage dependence of channel blockade results, at least in part, from the movement of K⁺ ions in the electrical field. A further quantitative analysis of the results explains why the complex phenomenon of inward rectification depends on both membrane voltage and the equilibrium potential for K⁺.