动物血红素过氧化物酶参与细菌氧化Mn(Ⅱ)的研究进展

锰氧化物是自然环境中一种重要的高活性矿物,在多种元素的生物地球化学循环中起着重要作用。细菌对锰氧化物的形成具有推动作用。截至目前,研究者已从环境中分离出多株锰氧化细菌,并在氧化机理的研究上取得了一定的进展。目前细菌中已知的锰氧化酶包括多铜氧化酶和动物血红素过氧化物酶。与多铜氧化酶相比,动物血红素过氧化物酶在蛋白结构与氧化方式上都具有自己的特点。本文结合国内外最新研究结果,在氧化菌株、氧化酶和基因、氧化方式及影响因素等方面对动物血红素过氧化物酶参与细菌氧化Mn(Ⅱ)的研究进行了总结,对未来研究方向进行了展望。     

Changes to the proteome and targeted metabolites of xylem sap in Brassica oleracea in response to salt stress

Root-to-shoot signalling via xylem sap is an important mechanism by which plants respond to stress. This signalling could be mediated by alteration in the concentrations of inorganic and/or organic molecules. The effect of salt stress on the contents of xylem sap in Brassica olarecea has been analysed by mass spectrometry in order to quantify these changes. Subcellular location of arabinogalactan proteins (AGPs) by immunogold labelling and peroxidase isozymes was also analysed by isoelectrofocusing. The xylem sap metabolome analysis demonstrated the presence of many organic compounds such as sugars, organic acids and amino acids. Of these, amino acid concentrations, particularly that of glutamine, the major amino acid in the sap, were substantially reduced by salt stress. The xylem sap proteome analysis demonstrated the accumulation of enzymes involved in xylem differentiation and lignification, such as cystein proteinases, acid peroxidases, and a putative hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyl transferase under salt stress. The peroxidase isozyme pattern showed that salt stress induced a high accumulation of an acid isoform. These results suggest that xylem differentiation and lignification is induced by salt stress. The combination of different methods to analyse the xylem sap composition provides new insights into mechanisms in plant development and signalling under salt stress.     

Ligninolytic activity of tropical rainforest basidiomycetes

A total of 116 strains of Brazilian tropical rainforest basidiomycetes were evaluated in terms of their ability to oxidize the dye rhemazol brilliant blue R (RBBR) and guaiacol. Laccase and peroxidase activities were detected by the drop test using solutions of α-naphthol and pyrogallol, respectively. RBBR and guaiacol oxidation occurred in 96.6 and 87.1% of the strains tested, respectively. One hundred strains oxidized both substrates. In the drop test, most strains presented laccase (96.6%) and peroxidase (92.2%) activity. The quick screening method used here can be useful to identify ligninolytic fungal strains to be used in various biotechnological applications. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effects of applied auxin,gibberellin and cytokinin on the activity of peroxidases in the peduncles of rose flowers

The activity of peroxidases in the proximal part of the flower peduncle of rose cv. Nubia was promoted by exogenous application of auxin but not by gibberellin or cytokinin. In cv. Mercedes the activity was promoted also by gibberellin and cytokinin. In the distal parts of the peduncles of both cultivars, peroxidase activity was not affected by any of the applied growth regulators. In young flowers of cv. Nubia the protein content of the penduncles was affected only by cytokinin, and in aged flowers only by auxin, while in Mercedes peduncles the content of protein was not affected by any of the applied growth regulators. The specific activity of peroxidases was promoted by auxin in peduncles of Nubia and by both auxin and cytokinin in peduncles of Mercedes flowers.     

Selenium unmasks protective iron armor: A possible defense against cutaneous inflammation and cancer

Background

A link between selenium deficiency and inflammatory skin diseases have been noted by many, but this link is still not well understood. We have previously studied the efficacy of ceramide analogs, based on the fire ant venom Solenopsin A, against our psoriasis animal model. Treatment of animals with solenopsin analogs resulted in significantly improved skin as well as in a coordinate downregulation of selenoproteins, namely Glutathione Peroxidase 4 (GPX4). We thus hypothesize that ferroptosis may be a physiologic process that may protect the skin from both inflammatory and neoplastic processes.

Changes in peroxidases in the suspension culture of Rubus fruticosus during growth

The growth parameters of a cell suspension culture of Rubus fruticosus L. were determined over a culture period including exponential growth, stationary phase and a glucose starvation period at the end of the normal culture cycle. Peroxidase activities were measured in the cytoplasm, in the cell wall, and in the culture medium by the guaiacol assay. There is a relationship between the activity found in the spent medium and the dry matter mass of the cells during the exponential growth. In the three compartments a bimodal repartition of peroxidase activities was observed, with the two peaks at day 4 and day 26, respectively. This suggests that the first peak corresponds to actively dividing cells whereas the second is associated with senescence, or stress due to starvation. Fractionation of the peroxidases from the culture mediuim revealed the presence of two sets of cationic isoenzymes, with minor amount of anionic peroxidases. Interestingly, the second peak of cationic enzymes which was of weak intensity at day 10 of the culture, becameprevalent at day 26. This indicates that not only the total amount of peroxidases varies as a function of culture time, but also that the nature of the peroxidases secreted into the medium changes during growth.Abbreviations DW dry weight - FW fresh weight - MV medium volume - SV suspension volume - BSA bovine serum albumin     

One- and two-electron oxidation of thiols: mechanisms,kinetics and biological fates

The oxidation of biothiols participates not only in the defense against oxidative damage but also in enzymatic catalytic mechanisms and signal transduction processes. Thiols are versatile reductants that react with oxidizing species by one- and two-electron mechanisms, leading to thiyl radicals and sulfenic acids, respectively. These intermediates, depending on the conditions, participate in further reactions that converge on different stable products. Through this review, we will describe the biologically relevant species that are able to perform these oxidations and we will analyze the mechanisms and kinetics of the one- and two-electron reactions. The processes undergone by typical low-molecular-weight thiols as well as the particularities of specific thiol proteins will be described, including the molecular determinants proposed to account for the extraordinary reactivities of peroxidatic thiols. Finally, the main fates of the thiyl radical and sulfenic acid intermediates will be summarized.     

Nickel toxicity and peroxidase activity in seedlings of Triticum aestivum L.

Ni²⁺ toxicity was evaluated in Triticum aestivum L. by its effects on root and shoot length, dry matter production and water content. Over a threshold value of 20 mmol m^?3 Ni²⁺ the degree of toxicity increases as a function of the Ni²⁺ concentration in the medium. Ni²⁺-treated roots show enhanced lipid peroxidation; the higher Ni²⁺ treatment (40mmol m^?3) also increases leakage of K⁺. In roots and shoots, Ni²⁺ enhances both guaiacol and syringaldazine extracellular peroxidase activity. The increase in extracellular peroxidase activity is also associated with an increase in the phenolic contents of roots and shoots. The observed growth inhibition might be partly the result of the effect of Ni²⁺ on cell turgor and cell-wall extensibility. Intracellular soluble peroxidases are also stimulated by Ni²⁺; such effects, independently of the substrate, were detected in extracts of Ni²⁺-treated shoots at a lower Ni²⁺ concentration than in the roots. Intracellular peroxidases might act as scavengers of peroxide radicals produced as a result of nickel toxicity.     

桑树MaGPX家族基因的克隆及表达分析

谷胱甘肽过氧化物酶(Glutathione peroxidases, GPXs)是植物细胞清除活性氧的重要酶类之一,与植物的抗逆性紧密相关。该研究以桑树(Morus alba L.)‘红果2号’为材料,利用RT PCR方法克隆了桑树MaGPX基因家族6个成员。生物信息学分析表明,MaGPX蛋白序列具有植物GPX的典型结构域和Cys残基,并与拟南芥(Arabidopsis thaliana)AtGPX蛋白序列具有较高的相似性。亚细胞定位结果表明,MaGPX1/2/3/6可能定位在细胞膜、细胞质和细胞核,MaGPX4定位在叶绿体,MaGPX5可能定位在细胞膜,暗示桑树MaGPX成员具有功能的分化。qRT PCR分析表明,MaGPX基因家族各成员在芽、叶、根、雄花、雌花以及果实中均有表达,其中MaGPX1/3/5在根以及雄花中高表达,MaGPX2在雄花中高表达,MaGPX4在叶和雄花中高表达,MaGPX6在果实中高表达;MaGPX各成员的表达受干旱胁迫诱导,各成员对干旱胁迫的响应随着处理时间和胁迫程度的变化而有所不同,其中MaGPX1、MaGPX2和MaGPX3可能在清除活性氧和维持细胞内氧化还原平衡中发挥重要作用。该研究结果为桑树MaGPX基因家族的生理功能研究奠定了良好基础。     

Co-occurrence of the multicopper oxidases tyrosinase and laccase in lichens in sub-order peltigerineae

BACKGROUND AND AIMS: Following previous findings of high extracellular redox activity in lichens and the presence of laccases in lichen cell walls, the work presented here additionally demonstrates the presence of tyrosinases. Tests were made for the presence of tyrosinases in 40 species of lichens, and from selected species their cellular location and molecular weights were determined. The effects of stress and inhibitors on enzyme activity were also studied. METHODS: Tyrosinase and laccase activities were assayed spectrophotometrically using a variety of substrates. The molecular mass of the enzymes was estimated using polyacrylamide gel electrophoresis. KEY RESULTS: Extracellular tyrosinase and laccase activity was measured in 40 species of lichens from different taxonomic groupings and contrasting habitats. Out of 20 species tested from the sub-order Peltigerineae, all displayed significant tyrosinase and laccase activity, while activity was low or absent in other species tested. Representatives from both groups of lichens displayed low peroxidase activities. Identification of the enzymes as tyrosinases was confirmed by the ability of lichen thalli or leachates derived by shaking lichens in distilled water to metabolize substrates such as L-dihydroxyphenylalanine (DOPA), tyrosine and epinephrine readily in the absence of hydrogen peroxide, the sensitivity of the enzymes to the inhibitors cyanide, azide and hexylresorcinol, activation by SDS and having typical tyrosinase molecular masses of approx. 60 kDa. Comparing different species within the Peltigerineae showed that the activities of tyrosinases and laccase were correlated to each other. Desiccation and wounding stimulated laccase activity, while only wounding stimulated tyrosinase activity. CONCLUSIONS: Cell walls of lichens in sub-order Peltigerineae have much higher activities and a greater diversity of cell wall redox enzymes compared with other lichens. Possible roles of tyrosinases include melanization, removal of toxic phenols or quinones, and production of herbivore deterrents.