Polarizable molecular mechanics studies of Cu(I)/Zn(II) superoxide dismutase: Bimetallic binding site and structured waters

The existence of a network of structured waters in the vicinity of the bimetallic site of Cu/Zn‐superoxide dismutase (SOD) has been inferred from high‐resolution X‐ray crystallography. Long‐duration molecular dynamics (MD) simulations could enable to quantify the lifetimes and possible interchanges of these waters between themselves as well as with a ligand diffusing toward the bimetallic site. The presence of several charged or polar ligands makes it necessary to resort to second‐generation polarizable potentials. As a first step toward such simulations, we benchmark in this article the accuracy of one such potential, sum of interactions between fragments Ab initio computed (SIBFA), by comparisons with quantum mechanics (QM) computations. We first consider the bimetallic binding site of a Cu/Zn‐SOD, in which three histidines and a water molecule are bound to Cu(I) and three histidines and one aspartate are bound to Zn(II). The comparisons are made for different His6 complexes with either one or both cations, and either with or without Asp and water. The total net charges vary from zero to three. We subsequently perform preliminary short‐duration MD simulations of 296 waters solvating Cu/Zn‐SOD. Six representative geometries are selected and energy‐minimized. Single‐point SIBFA and QM computations are then performed in parallel on model binding sites extracted from these six structures, each of which totals 301 atoms including the closest 28 waters from the Cu metal site. The ranking of their relative stabilities as given by SIBFA is identical to the QM one, and the relative energy differences by both approaches are fully consistent. In addition, the lowest‐energy structure, from SIBFA and QM, has a close overlap with the crystallographic one. The SIBFA calculations enable to quantify the impact of polarization and charge transfer in the ranking of the six structures. Five structural waters, which connect Arg141 and Glu131, are endowed with very high dipole moments (2.7–3.0 Debye), equal and larger than the one computed by SIBFA in ice‐like arrangements (2.7 D).     

人锰超氧化物歧化酶的紫外可见吸收光谱研究

研究了重组人锰超氧化物歧化酶(MnSOD)的紫外可见吸收光谱。经光学电负性和摩尔吸收系数分析,重新归属了酶中 Mn(Ⅲ)的可见光谱,首次报道了酶中Mn(Ⅱ)的电荷转移光谱。研究表明,MnSOD中显示的电荷转移谱带全部是由His咪唑基π轨道向金属轨道的LMCT跃迁。     

Photocytotoxic and anaerobic DNA cleavage activity of binuclear 3,3′-dithiodipropionic acid cobalt(II) complexes having phenanthroline bases

Dicobalt(II) complexes [{(B)Co^II}₂(μ-dtdp)₂] (1–3) of 3,3′-dithiodipropionic acid (dtdp) and phenanthroline bases (B), viz. 1,10-phenanthroline (phen in 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 3), have been prepared, characterized and their photo-induced anaerobic DNA cleavage activity studied. The elemental analysis and mass spectral data suggest binuclear formulation of the complexes. The redox inactive complexes have magnetically non-interacting dicobalt(II) core showing magnetic moment of ∼3.9 μ_B per cobalt(II) center. The complexes show good binding propensity to calf thymus DNA giving K_b values within 4.3 × 10⁵–4.0 × 10⁶ M⁻¹. Thermal melting and viscosity data predict DNA groove binding and/or partial intercalative nature of the complexes. The complexes show significant anaerobic DNA cleavage activity in green light under argon atmosphere possibly involving radical species generated from the disulfide moiety in a type-I pathway. The DNA cleavage reaction under aerobic medium in green light is found to involve hydroxyl radical species. The dppz complex 3 exhibits significant photocytotoxicity in HeLa cervical cancer cells with an IC₅₀ value of 2.3 μM in UV-A light of 365 nm, while it is essentially non-toxic in dark giving an IC₅₀ value of >200 μM. A significant reduction of the dark toxicity of the organic dppz base (IC₅₀ = 8.3 μM in dark) is observed on binding to the cobalt(II) center while essentially retaining its photocytotoxicity in UV-A light (IC₅₀ = 0.4 μM).     

测定超氧化物歧化酶活性的一种新的极谱分析方法

报道一种测定超氧化物歧化酶活生的新极谱分析方法，在０．１２５ｍｏｌ／ＬＮＨ３．Ｈ２Ｏ－０．７５ＭＯＬ／ｌ ｎｈ４ｃＬ－２．５％，Ｎａ２ＳＯ３－０．５％，吐温－８０－的介质中，ＳＯＤ在－０．５２Ｖ处产生一氧极谱催化波。ＳＯＤ在１．０×１０＾３Ｕ／Ｌ－４．０×１０＾３Ｕ／Ｌ的活性含量范围内与催化电流呈线性关系，检出限为８．０×１０＾２Ｕ／Ｌ。     

Highly Sensitive Spectrofluorimetric Determination of Trace Amounts of Superoxide Dismutase Using a Prulifloxacin-Terbium(III) Probe

Abstract

A new spectrofluorimetric method was developed for determining superoxide dismutase. The interactions between prulifloxacin (PUFX) –Tb³⁺ complex and superoxide dismutase had been studied by using UV-Vis absorption and fluorescence spectra. Using prulifloxacin–Tb³⁺ as a fluorescence probe, under optimum conditions, superoxide dismutase could remarkably enhance the fluorescence intensity of the prulifloxacin–Tb³⁺ complex at λ = 545 nm, and the enhanced fluorescence intensity was in proportion to the concentration of superoxide dismutase. Optimum conditions for the determination of superoxide dismutase were also investigated. The dynamic range for the determination of superoxide dismutase was 0.032 to 22.56 µg mL^?1, and the detection limit (S/N = 3) was 1.5 ng 4 mL^?1. This method was simple, practical, and relatively free of interference from coexisting substances and could be successfully used to determine superoxide dismutase in the plant and blood samples. The mechanism of fluorescence enhancement of prulifloxacin–Tb³⁺ complex by superoxide dismutase was also discussed.     

Superoxide Ion–Promoted Facile One-Pot Synthesis of O-Alkyl-S-methyl Dithiocarbonates from Alcohol Under Mild Reaction Conditions

Abstract

A new, mild, and efficient protocol for the one-pot synthesis of O-alkyl-S-methyl dithiocarbonates (xanthates) has been described in reasonably good yields from a variety of alcohols employing carbon disulfide and methyl iodide using superoxide ion at room temperature.

GRAPHICAL ABSTRACT     

富勒烯[60]膦酸酯衍生物纳米颗粒水悬液的制备与自由基清除活性

自由基清除是富勒烯及其衍生物的一种重要特性. 首次制备了1种二加成亚甲基富勒烯[60]膦酸酯衍生物(bis-methanophosphonate [60]fullerene, BMPF)的纳米颗粒水悬液(n-BMPF), 并采用邻苯三酚自氧化法结合分光光度法, 测定了n-BMPF对超氧阴离子自由基的清除作用. 结果显示, 制备的n-BMPF溶液较稳定, 适合生物学实验. 同时, 它表现出很强的清除超氧阴离子自由基的能力, 并具有浓度依赖性. 当n-BMPF的终浓度为12 μmol/L时, 其对超氧阴离子自由基的清除率达到91.96%. n-BMPF的活性远大于已报道具有自由基清除作用的水溶性富勒烯衍生物富勒醇. 这些数据表明n-BMPF可能作为一种新型高效的自由基清除剂, 在生物医学领域具有潜在的应用价值.     

Superoxide Anion Radical Scavenging Ability of Quaternary Ammonium Salt of Chitosan

A series of N-alky1 or N-ary1 chitosan quaternary ammonium salt were prepared using 96% deacetylated chitosan. Their scavenging activities against superoxide anion radical were investigated by chemiluminescence. The IC50 values of these compounds range from 280 to 880 μg/mL, which should be attributed to their different substitutes.     

Oxygen effects in aqueous solutions of laccases: Absorption spectra and reactivity

The optical absorption spectra of laccases in aqueous solutions were found to undergo reversible changes in the presence of O₂. It was suggested that dioxygen is coordinated in the active center of the completely oxidized native enzyme. Abnormal behavior of superoxide radical anions upon variation of the laccase concentration was found by pulse radiolysis. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1471–1474, August, 2000.     

邻苯三酚自氧化的电化学研究

用单扫示波极谱法测定了邻苯三酚在ＨＣｌ－Ｔｒｉｓ（ｐＨ８．３０）缓冲液中自氧化机理和其氧化产物的电化学行为，其自氧化产物在－０．１８Ｖ，－０．９６Ｖ和－１．４５Ｖ（ＳＣＥ）有三个还原波，并讨论了中药中部分有效成份对邻苯三酚自氧化产生的超氧自由基（Ｏ２）的清除作用。