谷胱甘肽/谷胱甘肽过氧化物酶系统在微生物细胞抗氧胁迫系统中的作用

谷胱甘肽(GSH)/谷胱甘肽过氧化物酶(GPx)系统在不同微生物细胞抵抗氧胁迫中的生理功能不尽相同。该系统在真核模式微生物酿酒酵母中是必需存在的,在维持胞内氧化还原平衡和抵抗氧胁迫中发挥主要作用。然而,在原核微生物中,该系统只是条件性的,即部分胞内存在谷胱甘肽还原酶和GPx的原核微生物,如流感嗜血杆菌和乳酸乳球菌,可通过从胞外吸收GSH,形成条件性的依赖于GSH的GPx系统,参与抵抗氧胁迫。     

水分胁迫对刺槐叶和根谷胱甘肽抗氧化系统的影响

在人工控水条件下,采用土壤最大持水量70%、55%、40%的水分处理模拟环境中的正常水分、轻度和重度水分胁迫处理,测定了刺槐叶片和根系中还原型谷胱甘肽(GSH)和还原型抗坏血酸(AsA)含量以及谷胱甘肽还原酶(GR)、谷胱甘肽过氧化物酶(GSH-Px)和超氧化物歧化酶(SOD)活性,以探讨水分胁迫条件下刺槐谷胱甘肽抗氧化系统的保护作用.结果显示:各水分处理的刺槐叶片GSH和AsA含量及GR 和SOD活性均明显高于根,根中GSH-Px活性只有在重度水分胁迫处理下大于叶片.随水分胁迫加剧,刺槐GSH含量在叶片中先升高后降低,在根中不断升高;AsA含量在叶中持续降低,在根中先升高后降低;GR活性在叶片和根系中都会降低,GSH-Px和SOD活性在叶中先升高后降低,在根中均持续升高.研究表明,刺槐谷胱甘肽抗氧化系统的GSH和GSH-Px对干旱胁迫诱发的活性氧清除起主要作用,同时提高GSH含量和GSH-Px活性是刺槐应对干旱胁迫的重要措施.     

过氧化氢胁迫促进产朊假丝酵母合成谷胱甘肽

谷胱甘肽(GSH)在生物细胞抵御外界环境条件的刺激和胁迫时起到非常重要的作用。考察了不同时间不同浓度过氧化氢胁迫和过氧化氢连续胁迫对产朊假丝酵母合成GSH的影响, 发现低浓度过氧化氢的连续胁迫对GSH的合成有明显促进作用。进一步在发酵罐上应用了低浓度过氧化氢(36 mmol/L)持续胁迫策略, 最终GSH产量为922 mg/L, 胞内GSH含量为1.64%, 比对照分别提高了7%和35%。     

过氧化氢胁迫促进产朊假丝酵母合成谷胱甘肽

谷胱甘肽(GSH)在生物细胞抵御外界环境条件的刺激和胁迫时起到非常重要的作用。考察了不同时间不同浓度过氧化氢胁迫和过氧化氢连续胁迫对产朊假丝酵母合成GSH的影响, 发现低浓度过氧化氢的连续胁迫对GSH的合成有明显促进作用。进一步在发酵罐上应用了低浓度过氧化氢(36 mmol/L)持续胁迫策略, 最终GSH产量为922 mg/L, 胞内GSH含量为1.64%, 比对照分别提高了7%和35%。     

高等植物体内的谷胱甘肽

谷胱甘肽(GSH)在植物对生物与非生物胁迫中起着重要的作用,其作用机制仍是国内外研究的热点之一。从GSH在植物体内的结构、代谢、功能及其分子生物学领域的研究作了综述,并对该领域存在的问题及前景作了展望。     

植物谷胱甘肽的生物合成及其生物学功能

谷胱甘肽(glutathione,GSH)是硫酸根还原同化途径中主要的含硫非蛋白终端产物,在生物中以还原型谷胱甘肽(reduced glutathione,GSH)和氧化型谷胱甘肽(oxidized glutathione,GSSG)存在。因其在植物体中的广泛存在和独特的还原能力得到广泛关注。本文从谷胱甘肽在植物体内的生物合成,谷胱甘肽的区划、运输和降解以及在非生物胁迫条件下的生物学功能等方面论述了近年来国内外对谷胱甘肽的研究进展。     

谷胱甘肽生物合成及代谢相关酶的研究进展

谷胱甘肽是广泛存在于生物体内的一个含有γ-肽键的生物活性三肽,其中游离的巯基是其活性中心。在生物体内谷胱甘肽主要是由GSH I和GSH II两个酶依次催化合成,而GSH I和GSH II的进化过程复杂,由此衍生出多条生物合成途径,其代谢过程在不同生物体内也复杂多样。本文主要综述了谷胱甘肽生物合成及代谢相关酶的研究进展和利用基因工程手段提高胞内谷胱甘肽含量的策略。     

具有高谷胱甘肽合成活性重组大肠杆菌的构建及合成反应过程

以野生型大肠杆菌E.coliⅡ为宿主细胞,转化带有编码谷胱甘肽合成酶系的基因gshⅠ和gshⅡ的质粒pGH501,获得了一株谷胱甘肽合成活性、质粒稳定性和传代稳定性俱佳,并且能够重复使用的重组大肠杆菌E.coliⅡ\|1。该菌株经过甲苯处理后,能够在胞外积累4g/L左右的谷胱甘肽(GSH)。在合成反应体系中,提高L谷氨酸浓度可促进GSH合成,但L半胱氨酸浓度增大到20mmol/L后会抑制GSH的合成。根据GSH合成反应中能量辅因子的变化情况,提出E.coliⅡ\|1细胞控制的GSH合成反应机理：由谷胱甘肽合成酶(GSHⅡ)控制的第二步反应的能量供体是ADP而非ATP,该反应是整个GSH合成反应的限速步骤,高浓度ADP可能会抑制GSHⅡ的活性。在GSH合成反应体系中添加100mmol/L的L丝氨酸-硼酸钾混合物,可以有效地防止GSH的进一步降解,反应3 h后,GSH产量达到230mmol/L(约71g/L)。     

外源NO对铜胁迫下番茄幼苗根系抗坏血酸-谷胱甘肽循环的影响

采用营养液培养方法,研究外源NO对铜胁迫下番茄(Lycopersicon esculentum Mill.)幼苗根系抗坏血酸(AsA)-谷胱甘肽(GSH)循环中抗氧化物质和抗氧化酶系的影响.结果表明:外施适量NO(硝普钠)可提高铜胁迫下番茄幼苗根系AsA、GSH含量和AsA/DHA(氧化型抗坏血酸)、GSH/GSSG(氧化型谷胱甘肽),降低DHA和GSSG含量.添加100 μmol·L-1 BSO(谷胱甘肽合成酶抑制剂)处理下,外源NO可提高铜胁迫下番茄幼苗根系的AsA含量、AsA/DHA及抗坏血酸酶(AAO)、单脱氢抗坏血酸还原酶(MDHAR)和脱氢抗坏血酸还原酶(DHAR)比活性,降低DHA、GSH、GSSG含量及抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)比活性;添加250 μmol·L-1 BSO处理下,外源NO提高了铜胁迫下番茄幼苗根系的AsA、GSH、GSSG含量、AsA/DHA及APX和GR比活性,降低了DHA含量及AAO、DHAR和MDHAR比活性.说明外源NO影响了铜胁迫下番茄根系的AsA-GSH代谢循环,并通过调节AsA/DHA、GSH/GSSG的变化来减轻氧化胁迫,从而缓解铜胁迫对番茄根系的伤害.     

谷胱甘肽在植物抗逆中的作用

在简要总结谷胱甘肽(GSH)的结构、分布、代谢和调控的基础上,概述了GSH在植物抗逆性方面的 作用,认为GSH通过植物体内螯合肽合成酶催化下聚合形成植物螯合肽来抵抗重金属的胁迫,作为抗氧化剂 参与低温伤害的保护,以亲核进攻一结合反应方式进行生物解毒等。讨论了GSH在植物抗逆性功能中的机 制,并就GSH今后在该方面的研究前景进行了展望。     

Glutathione transporters

Background

Glutathione (GSH) is synthesized in the cytoplasm but there is a requirement for glutathione not only in the cytoplasm, but in the other organelles and the extracellular milieu. GSH is also imported into the cytoplasm. The transports of glutathione across these different membranes in different systems have been biochemically demonstrated. However the molecular identity of the transporters has been established only in a few cases.

Scope of review

An attempt has been made to present the current state of knowledge of glutathione transporters from different organisms as well as different organelles. These include the most well characterized transporters, the yeast high-affinity, high-specificity glutathione transporters involved in import into the cytoplasm, and the mammalian MRP proteins involved in low affinity glutathione efflux from the cytoplasm. Other glutathione transporters that have been described either with direct or indirect evidences are also discussed.

Major conclusions

The molecular identity of a few glutathione transporters has been unambiguously established but there is a need to identify the transporters of other systems and organelles. There is a lack of direct evidence establishing transport by suggested transporters in many cases. Studies with the high affinity transporters have led to important structure-function insights.

General significance

An understanding of glutathione transporters is critical to our understanding of redox homeostasis in living cells. By presenting our current state of understanding and the gaps in our knowledge the review hopes to stimulate research in these fields. This article is part of a Special Issue entitled Cellular functions of glutathione.     

Glutathione peroxidases

Background

With increasing evidence that hydroperoxides are not only toxic but rather exert essential physiological functions, also hydroperoxide removing enzymes have to be re-viewed. In mammals, the peroxidases inter alia comprise the 8 glutathione peroxidases (GPx1–GPx8) so far identified.

Scope of the review

Since GPxs have recently been reviewed under various aspects, we here focus on novel findings considering their diverse physiological roles exceeding an antioxidant activity.

Major conclusions

GPxs are involved in balancing the H₂O₂ homeostasis in signalling cascades, e.g. in the insulin signalling pathway by GPx1; GPx2 plays a dual role in carcinogenesis depending on the mode of initiation and cancer stage; GPx3 is membrane associated possibly explaining a peroxidatic function despite low plasma concentrations of GSH; GPx4 has novel roles in the regulation of apoptosis and, together with GPx5, in male fertility. Functions of GPx6 are still unknown, and the proposed involvement of GPx7 and GPx8 in protein folding awaits elucidation.

General significance

Collectively, selenium-containing GPxs (GPx1–4 and 6) as well as their non-selenium congeners (GPx5, 7 and 8) became key players in important biological contexts far beyond the detoxification of hydroperoxides. This article is part of a Special Issue entitled Cellular functions of glutathione.     

Glutathione S-aralkyltransferase

1. The name `glutathione S-aralkyltransferase' is proposed for the enzyme catalysing the reaction of benzyl chloride with GSH. 2. Results from heat-inactivation studies, ammonium sulphate-fractionation and acid-precipitation experiments, and studies of the distribution of activities in rat liver, in rat kidney and in the livers of other animals indicate that glutathione S-aralkyltransferase differs from glutathione S-alkyltransferase, S-aryltransferase, S-epoxidetransferase and an S-alkenetransferase. 3. The distribution of these enzymes in the livers of the animal species examined was different. 4. Glutathione S-alkyltransferase, S-aralkyltransferase and the S-alkenetransferase that are present in rat liver supernatant were inhibited by GSSG, and the nature of the inhibition varied in each case. 5. 3,5-Di-tert.-butyl-4-hydroxybenzyl acetate reacts spontaneously with GSH, but the rat liver-supernatant-catalysed reaction of GSH with this and other aralkyl esters was weak. 6. A probable function of the glutathione S-transferases is the protection of cellular constituents from strong electrophilic agents.     

Glutathione monoesters

Glutathione monoesters in which the glycine carboxyl group is esterified are effective cellular glutathione delivery agents because they are readily transported into cells and are deesterified intracellularly. In contrast, glutathione itself is not effectively transported into cells. Detailed procedures are given for the preparation of such esters from glutathione and the corresponding alcohol using hydrogen chloride or sulfuric acid as the catalyst.