Vaccinia viral core inhibits Met-tRNAf·40S initiation complex formation with physiological mRNAs

Vaccinia viral core inhibits protein synthesis in reticulocyte lysates. In partial reactions using micrococcal nuclease treated reticulocyte lysates, the viral core inhibits Met-tRNA_f binding to 40S ribosomes in response to physiological mRNAs such as globin mRNA, cowpea mosaic viral RNA, and brome mosaic viral RNA but not in response to a trinucleotide codon, AUG. The core has also no effect on Met-tRNA_f binding to 40S ribosomes in a partial reaction using partially purified peptide chain initiation factors and AUG codon.The present observation of preferential inhibition by vaccinia viral core of Met-tRNA_f·40S initiation complex formation with physiological mRNAs and not with an artificial mRNA such as AUG codon, suggests that the viral core inhibits some step(s) in peptide chain initiation involved in the recognition of structural feature(s) unique to physiological mRNAs.     

Critical evaluation of electron transfer kinetics in P700–FA/FB, P700–FX, and P700–A1 Photosystem I core complexes in liquid and in trehalose glass

This work aims to fully elucidate the effects of a trehalose glassy matrix on electron transfer reactions in cyanobacterial Photosystem I (PS I). Forward and backward electron transfer rates from A_1A^? and A_1B^? to F_X, and charge recombination rates from A₀^?, A_1B^?, A_1A^?, F_X^?, and [F_A/F_B]^? to P₇₀₀⁺ were measured in P₇₀₀–F_A/F_B complexes, P₇₀₀–F_X cores, and P₇₀₀–A₁ cores, both in liquid and in a trehalose glassy matrix at 11% humidity. By comparing CONTIN-resolved kinetic events over 6 orders of time in increasingly simplified versions of PS I at 480?nm, a wavelength that reports primarily A_1A^?/A_1B^? oxidation, and over 9 orders of time at 830?nm, a wavelength that reports P₇₀₀⁺ reduction and A₀^? oxidation, assignments could be made for nearly all of the resolved kinetic phases. Trehalose-embedded PS I samples demonstrated partially arrested forward electron transfer. The fractions of complexes in which electron transfer did not proceed beyond A₀, A₁ and F_X were 53%, 16% and 22%, respectively, with only 10% of electrons reaching the terminal F_A/F_B clusters. The ~10?μs and ~150?μs components in both liquid and trehalose-embedded PS I were assigned to recombination between A_1B^? and P₇₀₀⁺ and between A_1A^? and P₇₀₀⁺, respectively. The kinetics and amplitudes of these resolved kinetic phases in liquid and trehalose-embedded PS I samples could be well-fitted by a kinetic model that allowed us to calculate the asymmetrical contribution of the A_1A^? and A_1B^? quinones to the electrochromic signal at 480?nm. Possible reasons for these effects are discussed.     

Thallium(III) complexes of the metalloligands [Pt2(μ-S)2(PPh3)4] and [Pt2(μ-Se)2(PPh3)4]

Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with the diarylthallium(III) bromides Ar₂TlBr [Ar = Ph and p-ClC₆H₄] in methanol gave good yields of the thallium(III) adducts [Pt₂(μ-S)₂(PPh₃)₄TlAr₂]⁺, isolated as their salts. The corresponding selenide complex [Pt₂(μ-Se)₂(PPh₃)₄TlPh₂]BPh₄ was similarly synthesised from [Pt₂(μ-Se)₂(PPh₃)₄], Ph₂TlBr and NaBPh₄. The reaction of [Pt₂(μ-S)₂(PPh₃)₄] with PhTlBr₂ gave [Pt₂(μ-S)₂(PPh₃)₄TlBrPh]⁺, while reaction with TlBr₃ gave the dibromothallium(III) adduct [Pt₂(μ-S)₂(PPh₃)₄TlBr₂]⁺[TlBr₄]⁻. The latter complex is a rare example of a thallium(III) dihalide complex stabilised solely by sulfur donor ligands. X-ray crystal structure determinations on the complexes [Pt₂(μ-S)₂(PPh₃)₄TlPh₂]BPh₄, [Pt₂(μ-S)₂(PPh₃)₄TlBrPh]BPh₄ and [Pt₂(μ-S)₂(PPh₃)₄TlBr₂][TlBr₄] reveal a greater interaction between the thallium(III) centre and the two sulfide ligands on stepwise replacement of Ph by Br, as indicated by shorter Tl-S and Pt?Tl distances, and an increasing S-Tl-S bond angle. Investigations of the ESI MS fragmentation behaviour of the thallium(III) complexes are reported.     

The effect of prostaglandins A2,E1,E2,15 methyl E2, 16, 16 dimethyl E2 and F2α on erythropoiesis

Prostaglandins A₂, E₁, E₂, methylated E₂s and F₂α affected erythropoiesis and/or erythropoietin (Ep) production. This action is indicated in the exhypoxic, polycythemic mouse where radioiron incorporations into RBC increased after administration of these compounds. The kidney and liver have been indicated through previous studies, to actively participate in Ep production. By the removal of one of these active sites in a murine system treated with prostaglandins it is shown that a response is reflected in Ep levels. Interference of the action of prostaglandins (PG) is altered by the removal of one of these target sites of Ep production. The erythropoietic responses elicited by PGA₂, E₁, and perhaps the methylated PGE₂s act through the liver whereas PGE₂ may operate through a renal pathway for its response. PGF_2α reveals no effect on erythropoietic activity and is no different than that observed for vehicle-treated controls. The prostaglandins tested appear to act primarily through the kidney or liver but the possibility exists that some yet undetermined organ site may also be involved.     

The arylation of [Pt2(μ-S)2(PPh3)4]

Routes to the synthesis of the mixed sulfide-phenylthiolate complex [Pt₂(μ-S)(μ-SPh)(PPh₃)₄]⁺ have been explored; reaction of [Pt₂(μ-S)₂(PPh₃)₄] with excess Ph₂IBr proceeds readily to selectively produce this complex, which was structurally characterised as its PF₆⁻ salt. Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with other potent arylating reagents (1-chloro-2,4-dinitrobenzene and 1,5-difluoro-2,4-dinitrobenzene) also produce the corresponding nitroaryl-thiolate complexes [Pt₂(μ-S){μ-SC₆H₂(NO₂)₂X}(PPh₃)₄]⁺ (X = H, F). The complex [Pt₂(μ-S)(μ-SPh)(PPh₃)₄]⁺ reacts with Me₂SO₄ to produce the mixed alkyl/aryl bis-thiolate complex [Pt₂(μ-SMe)(μ-SPh)(PPh₃)₄]²⁺, but corresponding reactions with the nitroaryl-thiolate complexes are plagued by elimination of the nitroaryl group and formation of [Pt₂(μ-SMe)₂(PPh₃)₄]²⁺. [Pt₂(μ-S)(μ-SPh)(PPh₃)₄]⁺ also reacts with Ph₃PAuCl to give [Pt₂(μ-SAuPPh₃)(μ-SPh)(PPh₃)₄]²⁺.     

Oxidation of [Ir(η-C5Me5)(C8H4S8)] and crystal structures of [IrI(η-C5Me5)(C8H4S8)](I3) and [IrI(η-C5Me5)(C8H4S8)](I3)1/2(I7)1/2

[Ir(η⁵-C₅Me₅)(C₈H₄S₈)] (1) [ = 2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithionate(2−)] was reacted with iodine in dichloromethane to afford one-electron- and two-electron-oxidized species [IrI(η⁵-C₅Me₅)(C₈H₄S₈)] (2), [IrI(η⁵-C₅Me₅)(C₈H₄S₈)](I₃) (3) and [IrI(η⁵-C₅Me₅)(C₈H₄S₈)](I₅) (4). The oxidized species exhibit electrical conductivities of (1.1-5.0) × 10⁻⁶ S cm⁻¹ measured for compacted pellets at room temperature. The X-ray crystal structures of the two-electron-oxidized complexes 3 and 4 revealed the Ir-I bonds for both of them and the presence of for 3 and ions for 4 as the counter anions. They have many S-S and S-I non-bonding contacts to form two-dimensional molecular interaction sheets in the solid state.     

Proton efflux through the chloroplast ATP synthase (CF0 · CF1) in the presence of sulfhydryl-modifying agents

The rate of photosynthetic electron transport measured in the absence of ADP and P_i is stimulated by low levels of Hg²⁺ or Ag⁺ (50% stimulation ≈ 3 Hg²⁺ or 6 Ag⁺/100 chlorophyll) to a plateau equal to the transport rate under normal phosphorylating conditions (i.e. +ADP, +P_i). Chloroplasts pretreated in the light under energizing conditions with N-ethylmaleimide show a similar stimulation of non-phosphorylating electron transport. The stimulations of non-phosphorylating electron transport by Hg²⁺, Ag⁺ and N-ethylmaleimide are reversed by the CF₁ inhibitor phlorizin, the CF₀ inhibitor triphenyltin chloride, and can be further stimulated by uncouplers such as methylamine. The Hg²⁺ and N-ethylmaleimide stimulations, but not the Ag⁺ stimulation, are completely reversed by low levels of ADP (2 μM), ATP (2 μM), and P_i (400 μM). Ag⁺, which is a potent inhibitor of ATP synthesis, has little or no effect upon phosphorylating electron transport (+ADP, +P_i). Concomitant with the stimulations of non-phosphorylating electron transport by Hg²⁺, Ag⁺ and ADP + P_i, there is a decrease in the level of membrane energization (as measured by atebrin fluorescence quenching) which is reversed when the CF₀ channel is blocked by triphenyltin. These results suggest that modification of critical CF₁ sulfhydryl residues by Hg²⁺, Ag⁺ or N-ethylmaleimide leads to the loss of intra-enzyme coupling between the transmembrane protontransferring and the ATP synthesis activities of the CF₀-CF₁ ATP synthase complex.     

Heterobimetallic platinum-bismuth aggregates derived from [Pt2(μ-S)2(PPh3)4]

The metalloligand [Pt₂(μ-S)₂(PPh₃)₄] reacts with Bi(S₂CNEt₂)₃ or Bi(S₂COEt)₃ in methanol to produce the orange cationic adducts [Pt₂(μ-S)₂(PPh₃)₄Bi(S₂CNEt₂)₂]⁺ and [Pt₂(μ-S)₂(PPh₃)₄Bi(S₂COEt)₂]⁺, respectively, isolated as their hexafluorophosphate salts. An X-ray structure determination on [Pt₂(μ-S)₂(PPh₃)₄Bi(S₂CNEt₂)₂]PF₆ reveals the presence of a six-coordinated bismuth centre with an approximately nido-pentagonal bipyramidal coordination geometry. Fragmentation pathways for both complexes have been probed using electrospray ionisation mass spectrometry; ions [Pt₂(μ-S)₂(PPh₃)₂Bi(S₂CXEt_n)₂]⁺ (X = O, n = 1, X = N, n = 2) are formed by selective loss of two PPh₃ ligands, and at higher cone voltages the species [(Ph₃P)PtS₂Bi]⁺ is observed. Ions formed by loss of CS₂ are also observed for the xanthate but not the dithiocarbamate ions.     

Synthesis of some pentanuclear platinum clusters [Pt5(CO)6(L)4]. The X-ray structure of [Pt5(μ-CO)5(CO)(PCy3)4]

[Pt₅(μ-CO)₅(CO)L₄] (L = PPh₃1, PPh₂Bz 2, AsPh₃3, PEt₃4, PCy₃5) have been synthesized by reacting [Pt₃(μ-CO)₃(PR₃)₃] with H₂O₂ (1 and 2), by reduction of cis-[PtCl₂(CO)(PEt₃)] with Zn dust (4), and by the Zn reduction of [Pt₃(μ-CO)₃(PCy₃)₃] in the presence of [PtCl₂(CH₃CN)₂] (5). Complex 5 has not been observed previously and has been characterized by X-ray crystallography. Oxidation of the phosphine ligands with H₂O₂ is a new way to synthesize 1 and 2. The first complete NMR characterization of these complexes has also been achieved, and showed that these pentanuclear cluster complexes exhibit similar stereochemistries in solution and in the solid state. The observed ¹J_Pt-Pt values do not have any correlation with the corresponding bond lengths, again pointing out the irregular behaviour of such parameter in Pt complexes.     

C3与C4植物的环境调控

环境条件决定着不同光合类型植物的地理分布范围和区域 ,一般来说 ,C4 植物分布于高温、强光的环境而 C3植物分布于阴凉、湿润的环境 ,且 C4 比 C3植物光合速率高。但环境条件影响着不同光合类型植物的光合潜能的发挥 ,C4 植物在高温、强光、干旱条件下所表现出来的优势在其它环境条件下未必就显现出来。环境条件甚至可以引起 C3、C4 光合途径间的相互转化 ,这使得目前几种鉴别植物光合类型的方法出现不一致的结果。因此 ,在判断植物的光合类型时 ,要注意多种手段的综合利用 ,同时注意植物所处环境条件的影响。     

Synthesis and structural characterization of the molecular loop [cis-Mo2(N,N-di-p-anisylformamidinate)2]2(O2C-CHCCH-CO2)2

A new molecular loop composed of two quadruply bonded Mo₂(DAniF)₂ units (DAniF=N,N^′-di-p-anisylformamidinate) linked by two chiral allene-1,3-dicarboxylate anions has been prepared from the reaction of [cis-Mo₂(DAniF)₂(MeCN)₄](BF₄)₂ with the bis(tetraethylammonium) salt of allene-1,3-dicarboxylic acid. This compound, [cis-Mo₂(DAniF)₂]₂(O₂C-CHCCH-CO₂)₂ (1), has been characterized by X-ray crystallography and by ¹H NMR and UV-Vis spectroscopy. The molecule possesses a center of inversion and hence is meso. There is only weak electronic coupling between the two Mo₂ ⁴⁺ units as revealed by electrochemical measurements.     

A versatile entry into aqueous niobium chemistry: isolation and structure of the intermediate Nb4(μ2-O)2(μ2-OC2H5)4Cl4(OC2H5)4(HOC2H5)4

The reduction of ethanolic solutions of niobium pentachloride with zinc, followed by treatment with aqueous acids serves as a versatile entry into the aqueous solution chemistry of niobium. From the zinc-reduced solution, the major intermediate, Nb₄(μ₂-O)₂(μ₂-OC₂H₅)₄Cl₄(OC₂H₅)₄(HOC₂H₅)₄, was isolated and the crystal structure determined by X-ray crystallography. The complex crystallizes in the orthorhombic space group Pccn, with Z=4, a=21.0105(9), b=11.0387(5), c=19.1389(8), V=4438.9(3) ų, M_r=1090.19,R₁=0.0327 and wR₂=0.0876. The structure revealed a centrosymmetric tetrameric Nb(IV) complex, consisting of a pair of edge-sharing bi-octahedral Nb₂(μ₂-OC₂H₅)₄Cl₂(OC₂H₅)₂(HOC₂H₅)₂ units that are joined by two axial oxo ligands. The Nb-Nb distance of 2.7458(3) Å is consistent with a single metal-metal bond.     

O -·2增强谷氨酸与其受体的结合力及EBSELEN的保护作用

用放射配体测定受体法研究了黄嘌呤(X)/黄嘌呤氧化酶(XO)体系产生的超氧阴离子自由基(O -·2)对［3H］DL-谷氨酸与大鼠大脑皮层突触膜谷氨酸受体结合的影响,结果表明O -·2明显增强谷氨酸与其受体的结合力,此作用能被2-苯基-1,2-苯并异硒唑-3(2H)酮(EBSELEN)(1 μmol/L)所抑制.     

Synthesis and characterisation of [Pt2(μ-S)(μ-I)(PPh3)4] - A cationic iodo analogue of the metalloligand [Pt2(μ-S)2(PPh3)4]

Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with a number of transition metal-iodo complexes leads to the formation of the cationic iodo analogue [Pt₂(μ-S)(μ-I)(PPh₃)₄]⁺, identified using electrospray ionisation mass spectrometry (ESI MS). Synthetic routes to this complex were developed, using the reaction of [Pt₂(μ-S)₂(PPh₃)₄] with either [PtI₂(PPh₃)₂] or elemental iodine. The complex was characterised by NMR spectroscopy, ESI MS and an X-ray structure determination, which reveals the presence of a planar, disordered {Pt₂SI}⁺ core. Monitoring the iodine reaction by ESI MS allows the identification of various iodine species, including the short-lived intermediate [Pt₂(μ-S)₂(PPh₃)₄I]⁺, which allows a mechanism for the reaction to be proposed.