东北地区蒿属植物比较形态学研究——II.叶表皮结构

本通过扫描电子显微镜,对东北地区蒿属（Ａｒｔｅｍｉｓｉａ）植物,莳萝蒿组（Ａ．ｓｅｃｔ．Ａｂｓｉｎｔｈｉｕｍ ＤＣ）,艾蒿组（Ｓｅｃｔ．Ａｂｒｏｔａｎｕｍ Ｂｅｓｓ）,艾组（Ｓｅｃｔ．Ａｒｔｅｍｉｓｉａ）,龙蒿组（Ｓｅｃｔ．Ｄｒａｃｕｍｃｕｌｕｓ Ｂｅｓｓ）,牡蒿组（Ｓｅｃｔ．ｌａｔｉｏｂｕｓ Ｙ．Ｒ．Ｌｉｎｇ）３６种成熟代表植物叶表皮形态学特征进行了详尽的比较研究。其中表皮细胞大小、形状不等。     

Molecular mechanism of diapause in insect (I) --Expression of diapause hormone gene and incubation temperature in embryonic stage of Bombyx mori

Ｉｎｓｅｃｔｓａｒｅｔｈｅｍｏｓｔｓｕｃｃｅｓｓｆｕｌａｎｉｍａｌｇｒｏｕｐｉｎｔｅｒｍｓｏｆｎｕｍｂｅｒｓｏｆｓｐｅｃｉｅｓ.Ａｌｔｈｏｕｇｈｍａｎｙｆａｃｔｏｒｓｍｕｓｔｃｏｎｔｒｉｂｕｔｅｔｏｔｈｅｐｒｏｆｕｓｉｏｎｏｆｉｎｓｅｃｔｓｐｅｃｉｅｓ,ｏｎｅｋｅｙｅｌｅｍｅｎｔｉｓｐｒｏｂａｂｌｙａｄｅｖｅｌｏｐｍｅｎｔａｌｐｌａｎｔｈａｔｉｎｃｏｒｐｏｒａｔｅｓｍｅｔａｍｏｒｐｈｏｓｉｓａｎｄｄｉａｐａｕｓｅ.Ｄｉａｐａｕｓｅｉｓａｃｏｍｐｌｅｘａｄａｐｔａｔｉｖｅｒｅｓｐｏｎｓｅｗｈｉｃｈｉ…     

凝血酶激活的单链尿激酶型纤溶酶原激活剂的构建、表达、纯化和性质研究

用Ｋｕｎｋｅｌ突变法,将单链尿激酶型纤溶酶原激活剂（ｓｃｕ－ＰＡ）ｃＤＮＡ基因中编码Ｐｒｏ１５５—Ｌｙｓ１５８的片段定点突变,并将此突变的ｓｃｕ－ＰＡ（ｔｓｃｕ－ＰＡ）的ｃＤＮＡ克隆到表达载体ｐＣＭ－β－ｎｅｏ中,与ｐＣＭ－ｄｈｆｒ共转染ＣＨＯ／ＤＨＦＲ－细胞．获得的稳定表达株在无血清培养基中２４ｈ的表达量为６２０ＩＵ／１０６细胞．经锌离子螯合Ｓｅｐｈａｒｏｓｅ亲和层析得到ｔｓｃｕ－ＰＡ纯品．ＳＤＳ－ＰＡＧＥ显示ｔｓｃｕ－ＰＡ分子量为５３ｋＤ左右,与预期的结果相符．ｔｓｃｕ－ＰＡ是由凝血酶激活而不是由纤溶酶激活,但激活后也能转变为双链分子（ｔｃｕ－ＰＡ）．ｔｓｃｕ－ＰＡ仍保持了ｓｃｕ－ＰＡ的血纤维蛋白亲和性．酶动力学研究表明,激活后的ｔｓｃｕ－ＰＡ水解Ｓ２４４４的Ｋｍ和Ｋｃａｔ值与高分子量尿激酶（ＨＵＫ）相似．体外溶栓实验结果表明,ｔｓｃｕ－ＰＡ可以选择性地溶解富含凝血酶的血凝块,对贫凝血酶的血凝块作用不大     

NifL,an antagonistic regulator of NifA interacting with NifA

Ｉｎｄｉａｚｏｔｒｏｐｈ,ｎｉｆｇｅｎｅｓａｒｅｐｏｓｉｔｉｖｅｌｙｒｅｇｕｌａｔｅｄｂｙｔｈｅｎｉｆＡｇｅｎｅｐｒｏｄｕｃｔＮｉｆＡ.ＲｈｉｚｏｂｉａＮｉｆＡｉｓｏｘｙｇｅｎｓｅｎｓｉｔｉｖｅ[1],ｙｅｔｓｏｍｅｏｆｔｈｅｍ,ｅ.ｇ.ＮｉｆＡｆｒｏｍＫ.ｐｎｅｕｍｏｎｉａｅ,Ｅ.ｃｌｏａｃａｅａｎｄＡ.ｖｉｎｅｌａｎｄｉｉ,ａｒｅｏｘｙｇｅｎｉｎｓｅｎｓｉｔｉｖｅ.Ｉｎｃｏｎｔｒａｓｔ,ｔｈｅｐｒｏｄｕｃｔｏｆｎｉｆＬ,ＮｉｆＬａｃｔｓａｓｒｅｐｒｅｓｓｏｒｆｏｒｎｉｆｇｅｎｅｓｉｎｔｈｅｐｒｅｓｅｎｃｅｏ…     

氨基酸集鱼剂与集鱼器

氨基酸集鱼剂与集鱼器范填基ＡｍｉｎｏＡｃｉｄＦｉｓｈＡｔｔｒａｃｔａｎｔｓａｎｄＡｔｔｒａｃｔｅｒ￥ＦａｎＺｈｅｎｊｉＡｂｓｔｒａｃｔｓ：ＴｈｉｓｐａｐｅｒｄｅｓｃｒｉｂｅｓｌｉｉｅｆｌｙｔｈｅｐｒｅｓｅｎｔｓｔａｔｕｓｏｆＡｍｉｎｏＡｃｉｄＦｉｓｈ...     

空气污染对植物病虫害的影响

空气污染对植物病虫害的影响吴亚,金翠霞（江苏省农科院植物保护研究所,南京２１００１４）ＥｆｆｅｃｔｓｏｆＡｔｍｏｓｐｂｅｒｉｃＰｏｌｌｕｔｉｏｎｏｎＰｌａｎｔＤｉｓｅａｓｅｓａｎｄＰｅｓｔｓ￥ＷｕＹａ;ＪｉｎＣｕｉｘｉａ（ＩｎｓｔｉｔｕｔｅｏｆＰｌａｎｔＰｒｏ－ｔｅｃｔｉｏｎ,ＪｉａｎｇｓｕＡｃａｄｅｍｙｏｆＡｇｒｉｃｕｌｔｕｒａｌＳｃｉｅｎｃｅｓ,Ｎａｎｊｉｎｇ２１００１４）．ＣｈｉｎｅｓｅＪｏｕｒｎａｌｏｆＥｃｏｌｏｇｙ,１９９３,１２（６）：４９－５３．Ｔｈｉｓｐａｐｅｒｓｕｍｍａｒｉｚｅｓｔｈｅｅｆｆｅｃｔｓｏｆｍａｉｎａｔｍｏｓｐｈｅｒｉｃｐｏｌｌｕｔａｎｔｓ,ｓｕｃｈａｓＯ＿３,ＳＯ＿２,ｆｌｕｏｒｉｄｅｓ,ａｃｉｄｒａｉｎｅｔｃ．ｏｎｐｌａｎｔｐａｔｈｏｇｅｎｉｃｍｉｃｒｏｏｒｇａｎｉｓｍｓ;ｔｈｅｅｆｆｅｃｔｓｏｆａｉｒｐｏｌｌｕｔｉｏｎｏｎｔｈｅｏｃｃｕｒａｎｃｅａｎｄｉｎｆｅｓｔａｔｉｏｎｏｆｐｈｙｔｏｐｈａｇｕｓｉｎｓｅｃｔｓ,ａｎｄｔｈｅｉｎｆｌｕｅｎｃｅｓｏｆｇｒｅｅｎｈｏｕｓｅｅｆｆｅｃｔｏｆＣＯ＿２ｏｎｔｈｅｏｕｔｂｒｅａｋｏｆｐｅｓｔｓ。Ｋｅｙｗｏｒｄｓ：ａｔｍｏｓｐｈｅｒｉ     

温度对麦长管蚜的影响

温度对麦长管蚜的影响汪世泽,郝树广（西北农业大学陕西杨陵７１２１００）ＥｆｆｅｃｔｓｏｆＴｅｍｐｅｒａｔｕｒｅｏｎＥｎｇｌｉｓｈＧｒａｉｎＡｐｈｉｄ￥．ＷａｎｇＳｈｉｚｅ;ＨａｏＳｈｕｇｕａｎｇ（ＮｏｒｔｈｗｅｓｔｅｒｎＡｇｒｉｃｕｌｔｕｒａｌＵｎｉｖｅｒｓｉｔｙ,Ｙａｎｇｌｉｎｇ,ＳｈａａｎｘｉＰｒｏｖｉｎｃｅ７１２１００）．ＣｈｉｎｅｓｅＪｏｕｒｎａｌｏｆＥｃｏｌｏｇｙ,１９９３,１２（３）：５３－５６．ＩｎａｎｅｘｐｅｒｉｍｅｎｔａｌｐｏｐｕｌａｔｉｏｎｏｆＥｎｇｌｉｓｈｇｒａｉｎａｐｈｉｄ,ｔｈｅｄｅｖｅｌｏｐｍｅｎｔｒａｔｅＶ（ｔ）ｏｆａｌａｔａｅｉｓｌｏｗｅｒｔｈａｎｔｈａｔｏｆａｐｔｅｒａｅ,ａｎｄｔｈｅＶ（ｔ）ｏｆ４ｔｈｉｎｓｔａｒｏｆａｌａｔａｅｉｓｔｈｅＩｏｗｅｓｔ．Ｔｈｅａｌａｔａｅａｐｐｅａｒｓｔｏｂｅａｂｌｅｔｏｔｏｌｅｒ－ａｔｅａｗｉｄｅｒｒａｎｇｅｏｆｔｅｍｐｅｒａｔｕｒｅ,ｂｕｔｔｈｅｓｕｒｖｉｖａｌｃｕｒｖｅｉｓａｆｆｅｃｔｅｄｅｖｉｄｅｎｔｌｙｂｙｉｔ．Ａｔｌｏｗｔｅｍｐｅｒａｔｕｒｅ,ｔｈｅｃｕｒｖｅｄｅｃｌｉｎｅｓｓｌｏｗｌｙ,ｂｕｔａｔｈｉｇｈｔｅｍｐｅｒａｔｕｒｅ     

湖南6种毛莨科植物的核型研究

本文对产于湖南的６种毛莨科植物的染色体进行了研究。裂叶星果草［Ａｓｔｅｒｏｐｙｒｕｍｃａｖａｌｅｒｉｅｉ（Ｌｅｖｌ．ｅｔＶａｎｔ）Ｄｒｕｍｍ．ｅｔＨｕｔｃｈ．）的染色体属于Ｒ型,核型公式为２ｎ＝１６＝１２ｍ＋２ｓｍ＋２ｔ,核型类型属于ＺＢ;打破碗花花（ＡｎｅｍｏｎｅｈｕｐｅｈｎｓｉｓＬｅｍ．）的核型公式为２ｎ＝１６＝１０ｍ＋４ｓｔ＋２ｔ（２ｓａｔ）,核型类型属于２Ａ;粗齿铁线莲［Ｃｌｅｍａｔｉｓａｐｉｉｆｏｌｉａｖａｒ．ａｒｇｅｎｔｉｌｕｃｉｄａ（Ｌｅｖｌ．ｅｔＶａｎｔ）Ｗ．Ｔ．Ｗａｎｇ］的核型公式为２ｎ＝１６＝１０ｍ＋２ｓｔ＋４ｔ（２ｓａｔ）或２ｎ＝１６＝１０ｍ＋２ｓｔ＋４ｔ（４ｓａｔ）随体染色体数目在居群之间有变化,核型类型属于２Ａ;扬子铁线莲［Ｃｌｅｍａｔｉｓｇａｎｉｐｉｎｉａｎａ（Ｌｅｖｌ．ｅｔＶａｎｔ）Ｔａｍｕｒａ］的核型公式为２ｎ＝１６＝１０ｍ＋２ｓｔ＋４ｔ（４ｓａｔ）,核型类型属于２Ｂ;毛莨（ＲａｎｕｎｃｕｌｕｓｃａｎｔｏｎｉｅｎｓｉｓＤＣ．）的核型公式为２ｎ＝１６＝６ｍ＋４ｓｔ＋６ｓｔ（２ｓａｔ）,核型类型属于３Ａ;毛莨（ＲａｎｕｎｃｕｌｕｓｊａｐｏｎｉｃｕｓＴｈｕｎｂ．）的核型公式为２ｎ＝?     

沈阳市东陵区丘陵坡地坡面太阳直射光的分布及其分析

沈阳市东陵区丘陵坡地坡面太阳直射光的分布及其分析郭林海（中国科学院沈阳应用生态研究所,１１００１５）ＤｉｓｔｒｉｂｕｔｉｏｎｏｆＤｉｒｅｃｔＳｏｌａｒＲａｄｉａｔｉｏｎｏｎＨｉｌｌｙＳｌｏｐｅｓｏｆＤｏｎｇｌｉｎｇＤｉｓｔｒｉｃｔｏｆＳｈｅｎｙａｎｇＭｕｎｉｃｉｐａｌｉｔｙａｎｄＩｔｓＡｎａｌｙｓｉｓ￥ＧｕｏＬｉｎｈａｉ（ＩｎｓｔｉｔｕｔｅｏｆＡｐｐｌｉｅｄＥｃｏｌｏｇｙ,ＡｃａｄｅｍｉａＳｉｎｉｃａ,Ｓｈｅｎｙａｎｇ１１００１５）．ＣｈｉｎｅｓｅＪｏｕｒｎａｌｏｆＥｃｏｌｏｇｙ,１９９３,１２（１）：５９－６１．Ｂａｓｅｄｏｎｔｈｅｌａｔｅｓｔ１：５００００ｔｏｐｏｇｒａｐｈｉｃｍａｐ,ｔｈｅ１：１０００００ｓｌｏｐｅｇｒａｄａｔｉｏｎｍａｐｉｓｄｒａｗｎｏｕｔａｎｄａｒｅａｃａｌｃｕｌａｔｉｏｎｉｓｍａｄｅ．Ｔｈｅｄｉｒｅｃｔｓｏｌａｒｒａｄｉａｔｉｏｎｉｎｔｙｐｉｃａｌｓｉｔｅｓｏｆｔｈｅｄｉｓｔｒｉｃｔｉｓｍｅａｓｕｒｅｄａｎｄｃａｌｃｕｌａｔｅｄ,ａｎｄｔｈｅｖａｒｉａｔｉｏｎｃｕｒｖｅｓｏｆａｎｎｕａｌｆｌｕｘｏｆｄｉｒｅｃｔｓｏｌａｒｒａｄｉａｔｉｏｎｏｎｖａｒｉｏｕｓｓｌｏｐｅｄｉｒｅｃｔｉ     

吉林省产5种百合的核型研究

报道了吉林省产５种百合科植物的染色体数目和核型：①毛百合Ｌｉｌｉｕｍ ｄａｕｒｉｃｕｍ Ｋｅｒ．－Ｇｅｗ１．２ｎ＝２４＝２ｍ（２ＳＡＴ）＋２ｓｍ（２ＳＡＴ）＋８ｓｔ（２ＳＡＴ）＋１２ｔ（２ＳＡＴ）;②有斑百合Ｌ．ｃｏｎｃｏｌｏｒ Ｓａｌｉｓｂ．ｖａｒ．ｂｕｓｃｈｉａｎｕｍ（Ｌｏｄｄ．）Ｂａｋｅｒ ２ｎ＝２４＝２ｍ（２ＳＡＴ）＋４ｓｍ（４ＳＡＴ）＋６ｓｔ（２ＳＡＴ）＋１２ｔ;③兰州百合Ｌ．ｄａｖｉｄ     

从人发中连续提取亮氨酸和胱氨酸工艺初探

介绍了一种从人发中连续提取亮氨酸和胱氨酸的新工艺。人发用盐酸水解后 ,将水解液减压赶酸 ,再直接加入邻二甲苯 - 4-磺酸沉淀亮氨酸 ,所得沉淀经氨解及后续的精制过程可得亮氨酸精品 ,沉淀亮氨酸后所得的母液按传统的工艺用液氨和得胱氨酸粗品 ,再经一次精制中和可得胱氨酸精品。亮氨酸和胱氨酸的收率分别可达 4 .9%和 7.8% ,产品质量符合日本味之素标准     

Chlorination studies II. The reaction of aqueous hypochlorous acid with α-amino acids and dipeptides

HOCl by oxidative decarboxylation converts several α-amino acids into a mixture of the corresponding nitriles (major) and aldehydes (minor product). In addition, chlorination of the ring of tyrosine was observed. Cysteine when reacted with HOCl yielded cystine and cysteic acid, while with cystine, cysteic acid was the only product identified. The nitrogen bond of several dipeptides was found to be resistant to aqueous HOCl at room temperature. Chlorination of these compounds gave the corresponding N,N-dichlorodipeptide.     

Expression of gamma-glutamyltransferase 1 in glioblastoma cells confers resistance to cystine deprivation–induced ferroptosis

Ferroptosis is an iron-dependent mode of cell death caused by excessive oxidative damage to lipids. Lipid peroxidation is normally suppressed by glutathione peroxidase 4, which requires reduced glutathione. Cystine is a major resource for glutathione synthesis, especially in cancer cells. Therefore, cystine deprivation or inhibition of cystine uptake promotes ferroptosis in cancer cells. However, the roles of other molecules involved in cysteine deprivation–induced ferroptosis are unexplored. We report here that the expression of gamma-glutamyltransferase 1 (GGT1), an enzyme that cleaves extracellular glutathione, determines the sensitivity of glioblastoma cells to cystine deprivation–induced ferroptosis at high cell density (HD). In glioblastoma cells expressing GGT1, pharmacological inhibition or deletion of GGT1 suppressed the cell density–induced increase in intracellular glutathione levels and cell viability under cystine deprivation, which were restored by the addition of cysteinylglycine, the GGT product of glutathione cleavage. On the other hand, cystine deprivation induced glutathione depletion and ferroptosis in GGT1-deficient glioblastoma cells even at an HD. Exogenous expression of GGT1 in GGT1-deficient glioblastoma cells inhibited cystine deprivation–induced glutathione depletion and ferroptosis at an HD. This suggests that GGT1 plays an important role in glioblastoma cell survival under cystine-limited and HD conditions. We conclude that combining GGT inhibitors with ferroptosis inducers may provide an effective therapeutic approach for treating glioblastoma.     

Utilization of cystine by dermatophytes on glucose-peptone media

All the 16 strains of dermatophytes tested here metabolized cystine (3 mmol/L) in two glucose-peptone media with a different C: N ratio. Cystine was utilized as a sulfur source and, in addition, as a carbon and nitrogen source, in parallel with growth. Excess sulfur was excreted to the medium after its oxidation as inorganic sulfate and sulfite. In a physiologically alkaline medium the growth was fast and was accompanied by a pH increase and cystine was utilized intensively. Eleven species used up all cystine available. Sulfate was the main oxidation product, sulfite was produced at a low concentration, at the beginning of growth in particular. Only traces of thiol compounds (cysteine) were present in the medium. In a physiologically acid medium growth was soon limited by a decreased pH (below 5.0) but cystine continued to be utilized at an identical rate. All cystine was used up by 5 species. The tendency to produce sulfite in addition to sulfate further increased and sulfite was often the predominant product. Concentrations of thiol compounds were also substantially higher. Thus, dermatophytes can utilize cystine even under conditions that do not support good growth and increase the sulfite production.     

Structural and biochemical analyses of Microcystis aeruginosa O-acetylserine sulfhydrylases reveal a negative feedback regulation of cysteine biosynthesis

O-acetylserine sulfhydrylase (OASS) catalyzes the final step of cysteine biosynthesis from O-acetylserine (OAS) and inorganic sulfide in plants and bacteria. Bioinformatics analyses combined with activity assays enabled us to annotate the two putative genes of Microcystis aeruginosa PCC 7806 to CysK1 and CysK2, which encode the two 75% sequence-identical OASS paralogs. Moreover, we solved the crystal structures of CysK1 at 2.30 ? and cystine-complexed CysK2 at 1.91 ?, revealing a quite similar overall structure that belongs to the family of fold-type II PLP-dependent enzymes. Structural comparison indicated a significant induced fit upon binding to the cystine, which occupies the binding site for the substrate OAS and blocks the product release tunnel. Subsequent enzymatic assays further confirmed that cystine is a competitive inhibitor of the substrate OAS. Moreover, multiple-sequence alignment revealed that the cystine-binding residues are highly conserved in all OASS proteins, suggesting that this auto-inhibition of cystine might be a universal mechanism of cysteine biosynthesis pathway.     

Pyrolysis of Sulfur-containing Amino Acids

Sulfur-containing amino acids (l-cysteine, l-cystine and dl-methionine) were pyrolyzed. From pyrolyzed cysteine and cystine were identified 7~8 volatile compounds including 2-methylthiazolidine which is considered to be the product of the reaction of acetaldehyde with mercaptethylamine, and from pyrolyzed methionine were identified 11 volatiles. At the same time, besides these volatile compounds, alanine, cystine and isoleucine, and alanine, isoleucine and methionine were detected in the pyrolyzed products of cysteine and cystine, respectively, but no amino acid was detected from that of methionine. The mixture of seven identified volatiles generated from l-cystine developed a pop-corn like aroma with a roasted sesame like one, and methylmercaptane seemed to be the main contributor to the pickled radish like odor produced from pyrolysis of dl-methionine. Degradation schemes of cystine and methionine were proposed.     

Interference of azide with cysteine biosynthesis in Salmonella typhimurium.

The growth inhibition of Salmonella typhimurium aziA mutants by sodium azide is reversed by cystine and related compounds. NADPH-sulphite reductase (hydrogen-sulphide:NADP+ oxidoreductase; EC 1.8.1.2), an enzyme of cysteine biosynthesis, is inhibited in cell extracts by sodium azide. AziB mutants which are able to grow in the presence of the inhibitor without cystine were isolated. About half of them were mapped in the cysK gene and have only residual activity of its product, O-acetylserine sulphydrylase A [O-acetyl-L-serine acetate-lyase (adding hydrogen-sulphide); EC 4.2.99.8]. Sensitivity of wild type and aziA mutants to azide was also reversed by a constitutive mutation in cysB, the regulatory gene of cysteine biosynthesis. CysK and cysB mutants showed cross-resistance to azide and 1,2,4-triazole. It is suggested that the resistance of these mutants to azide is due to an increased activity of NADPH-sulphite reductase.     

Design,pharmacology, and NMR structure of a minimized cystine knot with agouti-related protein activity

The agouti-related protein (AGRP) is an endogenous antagonist of the melanocortin receptors MC3R and MC4R found in the hypothalamus and exhibits potent orexigenic activity. The cysteine-rich C-terminal domain of this protein, corresponding to AGRP(87-132), exhibits receptor binding affinity and antagonism equivalent to that of the full-length protein. The NMR structure of this active domain was recently determined and suggested that melanocortin receptor contacts were made primarily by two loops presented by a well-structured cystine knot domain within AGRP(87-132) [McNulty et al. (2001) Biochemistry 40, 15520-15527]. This hypothesis is tested here with NMR structure and activity studies of a 34-residue AGRP analogue designed to contain only the cystine knot domain. The designed miniprotein folds to a homogeneous product, retains the desired cystine knot architecture, functions as an antagonist, and maintains the melanocortin receptor pharmacological profile of AGRP(87-132). The AGRP-like activity of this molecule supports the hypothesis that indeed the cystine knot region possesses the melanocortin receptor contact points. Moreover, this potent AGRP analogue is synthetically accessible, may serve in the development of therapeutics for the treatment of diseases related to energy balance. and may also find use as a new reagent for probing melanocortin receptor structure and function.     

Action of Cystine in the Cytotoxic Response of Escherichia Coli Cells Exposed to Hydrogen Peroxide

Cystine markedly enhanced the cytotoxic response of Escherichia coli cells to concentrations of hydrogen peroxide resulting in mode one killing, but displayed little effect in mode two killed cells. The effect of cystine was concentration-dependent over a range of 5-50 μM and did not further increase at higher levels. Cystine had similar effects in other bacterial systems.

In order to sensitize the cells to the oxidative injury, the amino acid must be present during exposure to the oxidant since no enhancement of the cytotoxic response can be observed in cystine pre-loaded cells. In addition, no further enhancement of cytotoxicity could be detected when cystine was added before and left during challenge with the oxidant. The enhancing effect of cystine on oxidative injury of E. coli cells appears to be directly mediated by the amino acid and in fact cysteic acid, the most likely oxidation product, had no effect on the killing of bacterial cells elicited by hydrogen peroxide. Other disulfide compounds such as oxidized glutathione, cystamine and dithionitrobenzoic acid only slightly increased the susceptibility of bacteria to the oxidant. The effect of the disulfides was not concentration-dependent over a range of 200-800 μM and was statistically significant only for cystamine.

Taken together, these results indicate that cystine markedly increases the cytotoxic response of bacteria to hydrogen peroxide and suggest that the amino acid might impair the cellular defence machinery against hydrogen peroxide. This effect may involve a thiol-disulfide exchange reaction at the cell membrane level.