竹红菌甲素（HA）光敏致实作用的研究

以中国苍鼠卵巢成纤维细胞（ＣＨＯ）为材料,通过ＨＡ光敏诱变,乌本甙（ｏｕａｂａｉｎ）筛选研究了竹红菌甲素光敏反应对细胞Ｎａ＋／Ｋ＋ＡＴＰ酶基因的诱变致灾作用。结果表明ＨＡ光敏反应可造成细胞Ｎａ＋／Ｋ＋ＡＴＰ酶基因点突变,并具有遗传稳定性。另外通过测定光敏反应细胞脂质过氧化程度及其产物与细胞ＤＮＡ形成的荧光产物表明脂质过氧化在细胞ＤＮＡ的损伤突变过程中,起着重要的作用。     

膜脂过氧化产物在光敏诱发细胞突变中的作用

本文选用ＣＨＯ细胞,通过竹红菌甲素（ＨＡ）光敏诱变及ｏｕａ选择性培养液的筛选,证实甲素光敏反应对细胞Ｎａ＾＋／Ｋ＾＋ ＡＴＰ酶基因具有诱变致突作用。对其突变效应与脂质过氧化反应及ＤＮＡ加成物形成关系的分析表明,ＴＢＡ反应产物随着光照时间的增加而增加,同时ＤＮＡ加成物生成迅速增加,突变频率也随之增高。维生素Ｅ可抑制脂质过氧化反应,并减少ＤＮＡ加成物生成,阻止细胞突变率的增加。提示光敏诱发细胞脂质过氧     

NaCl胁迫高粱根,叶鞘和叶片液泡膜ATP酶和焦磷酸酶活性的影响

ＮａＣｌ胁迫初期,Ｎａ＾＋主要在根和叶鞘中积上应地,根和叶鞘液泡膜ＡＴＰ酶和焦磷酸酶水解活性、依赖ＡＴＰ和ＰＰｉ的质子泵活性及Ｎａ＾＋／Ｈ＾＋逆向转运活性均明显增加,根和叶鞘的生长没有受到抑制。ＮａＣｌ胁迫后期,Ｎａ＾＋开始向地上部分运输并在叶片中积累,此时,叶片液泡膜质子泵和Ｎａ＾＋／Ｈ＾＋逆向转运活性开始增加,根和叶鞘的Ｎａ／Ｋ比增加,其液泡膜ＡＴＰ酶和焦磷酸水解活性、质子泵活性和Ｎａ＾＋／Ｈ     

铝和铝＋钙对小麦幼苗根尖质膜,液泡膜微囊ATP酶和膜流动性？…

研究了铝和铝＋＿钙对小麦功苗根尖质膜、液泡膜微囊Ｈ＾＋－ＡＴＰ酶、Ｃａ＾２＋－ＡＴＰ酶、Ｍｇ＾２＋－ＡＴＰ酶活性及共动力学参数和膜流动性的影响。在质膜和液泡膜微囊制剂中加入１．０ｍｍｏｌ／Ｌ的ＡＩ＾３＋（ＡＩＣＩ３）时,Ｈ＾２＋－ＡＴＰ囊制剂中加入１．０ｍｍｏｌ／Ｌ的ＡＩ＾３＋（ＡＩＣＩ３）时,Ｈ＾＋－ＡＴＰ酶、Ｃａ＾２＋－ＡＴＰ酶、Ｍｇ＾２＋－ＡＴＰ酶活笥和酶促反应的Ｖｍａｘ及膜流动性下降,而酶     

天然抗氧化剂丹参酮Ⅱ—A对肝细胞脂质过氧化产物与DNA相互作用的影响

［＾３Ｈ］花生四烯酸标记的肝细胞,经ＦｅＣｌ２－ＤＴＰＡ启动脂质过氧化后,细胞ＤＮＡ出现放射性,并随保温时间增加而逐渐增高,表明在细胞内脂质过氧化产物与ＤＮＡ发生相互作用,生成了一种ＤＮＡ加成物,经测定它具有特征荧光光谱,显示较低的增色效应和Ｔｍ值。用高度敏度荧光图象显微镜直接观察发现丹参酮Ⅱ－Ａ经细胞摄取后主要滞留在细胞膜与胞浆中。它能有效地抑制细胞脂质过氧化,减少脂质－ＤＮＡ加成物的产生,并阻     

玉米根细胞膜铁氰化钾还原酶

玉米根细胞膜制剂具有明显的ＮＡＤＨ－铁氰化钾还原酶活性,铁氰化钾补还原的同时伴有质子跨膜运输,所形成的△μＨ＾＋既不受Ｈ＾＋－ＡＴＰａｓｅ抑制剂的影响。也不需要ＡＴＰ的存在,反应最适ｐＨ为６．５。ＦＣＲ对ＮＡＤＨ和铁氰化钾具有较高的活性反应而对ＮＡＤＰＨ只有微弱的反应活性。ＦＣＲ的潜在活性证实在膜的胞侧存在底物结合部位。Ｍｇ＾２＋,Ｍｎ＾２＋,Ｃａ＾２＋,Ｋ＾＋,Ｎａ＾＋对酶均有一定的激活作用,以     

布氏田鼠冷暴露中的适应性产热机理

布氏田鼠急性冷暴露,在最初２小时内体温明显下降,冷驯化２８天后,体温相对稳定。冷暴露１天,动物的褐色脂肪组织蛋白量明显增加,ｃＡＭＰ含量及Ｎａ＾＋／Ｋ＾＋－ＡＴＰ酶活力明显升高。２８天冷驯化动物的褐色脂肪组织重量明显增加,ｃＡＭＰ含量增加更高,蛋白量、Ｎａ＾＋／Ｋ＾＋－ＡＴＰ酶活力以及Ｔ４５‘－脱碘酶活力均显著提高,揭示了褐色脂肪组织的产热机理。     

鼠脑突触体Mg^2＋—ATP酶质子泵活性的研究

位于突触体质膜的外向型（ｅｃｔｏ）Ｍｇ＾２－ＡＴＰ酶具有水解ＡＴＰ活性,能量偶联的ＡＣ－ＭＡ荧光淬灭实验表明Ｍｇ＾２＋－ＡＴＰ酶水解ＡＴＰ时向膜内转移质子,建立跨膜质子梯度,跨膜质子梯度可以被电中性Ｋ＾＋／Ｈ＾＋离子载体Ｎｉｇｅｒｉｃｉｎ消除,利用Ｈ＾＋敏感的ＢＣＥＣＦ荧光分子测定突触的ｐＨｉ变化,结果表明水解ＡＴＰ产生的质子转移突触体ｐＨｉ下降了光分子测定突触的ｐＨｉ变化,结果表示水解ＡＴＰ产生     

大鼠胰腺β细胞离子通道的一些特性

实验以单个Ｗｉｓｔａｒ大鼠胰腺β细胞为对象,用穿孔膜片箝和细胞贴附式记录技术研究ＡＴＰ敏感Ｋ＾＋通道（ＫＡＴＰ）、延迟整流型Ｋ＾＋通道（ＫＤＲ）、Ｃａ＾２＋通道和Ｎａ＾＋通道的有关特性。结果表明：⑴ＫＡＴＰ通道的内流电导约６５ｐＳ,外流电导约３１ｐＳ,反转电位在－６０ｍＶ左右;⑵ＫＤＲ通道在延迟２０ｍｓ后达到最大激活,ＫＤＲ电流约为ＫＡＴＰ的１／３;⑶钙电流在０ｍＶ左右达到４０－６０ｐＡ的峰值,Ｌ     

盐胁迫下钙对大麦根系质膜和液泡膜功能的保护效应（简报）

盐胁迫下外加钙可增强大麦根系质膜液泡膜Ｈ＾＋－ＡＴＰａｓｅ、液泡膜质子泵和Ｎａ＾＋／Ｈ＾＋逆向运输活性,促进根系对Ｋ＾＋的选择性吸收和运输,降低叶片的Ｎａ＾＋／Ｋ＾＋比。     

Peroxyl radical mediated oxidative DNA base damage: implications for lipid peroxidation induced mutagenesis

Endogenous DNA damage induced by lipid peroxidation is believed to play a critical role in carcinogenesis. Lipid peroxidation generates free radical intermediates (primarily peroxyl radicals, ROO(*)) and electrophilic aldehydes as the principal genotoxicants. Although detailed information is available on the role of aldehyde base adducts in mutagenesis and carcinogenesis, the contribution of peroxyl radical mediated DNA base damage is less well understood. In the present study we have mapped oxidative base damage induced by peroxyl radicals in the supF tRNA gene and correlated this information with peroxidation-induced mutations in several human fibroblast cell lines. Nearly identical patterns of oxidative base damage were obtained from reaction of DNA with either peroxidizing arachidonic acid (20:4omega6) or peroxyl radicals generated by thermolysis of ABIP in the presence of oxygen. Oxidative base damage primarily occurred at G and C. Transversions at GC base pairs in the supF gene were the major base substitution detected in all cell lines. Peroxyl radical induced tandem mutations were also observed. Many mutation hot spots coincided with sites of mapped oxidative lesions, although in some cases hot spots occurred adjacent to the damaged base. Evidence is presented for the involvement of 8-oxodG in the oxidation of DNA by ROO(*). These results are used to interpret some key features of previously published mutation spectra induced by lipid peroxidation in human cells.     

17beta-estradiol suppresses ROS-induced apoptosis of CHO cells through inhibition of lipid peroxidation-coupled membrane permeability transition

Oxidative stress-induced apoptotic cell death has been implicated to play a critical role in the mechanism of corpus luteum regression and follicular atresia. Recent studies suggests that reactive oxygen species (ROS) might play important roles in the regulation of luteal function. The present work describes the inhibitory effect of 17beta-estradiol (E2) on ROS-induced mitochondrial membrane permeability transition (MPT) and apoptosis of Chinese hamster ovary (CHO) cells. ROS generated by Fe2+ and H2O2 induced mitochondrial lipid peroxidation, depolarization, activation of caspase-3 and DNA fragmentation in CHO cells by some E2-inhibitable mechanism. E2 suppressed the Fe2+/H2O2-induced lipid peroxidation and MPT of isolated mitochondria that was characterized by cyclosporin A-inhibitable swelling, depolarization and cytochrome c release. Furthermore, E2 scavenged the xanthine oxidase generated ROS. These results suggests that Fe2+/H2O2 induced MPT and apoptosis of CHO cells by a mechanism that could be suppressed by antioxidant properties of E2.     

Molecular and genetic characterization of an ornithine decarboxylase-deficient Chinese hamster cell line.

The ornithine decarboxylase (ODC)-deficient Chinese hamster ovary (CHO) cell line C55.7 has normal amounts of ODC mRNA with very low amounts of immunologically detectable ODC protein, suggesting a structural mutation; however, 5-azacytidine treatment leads to phenotypical reversion (Steglich, C., and Scheffler, I. E. (1985) Somat. Cell Mol. Genet. 11, 11-23). We have demonstrated by chemical cleavage a single base mismatch in DNA heteroduplexes composed of wild-type and mutant cDNA strands. DNA sequencing showed that the mutant phenotype results from an aspartate-glycine substitution at amino acid 381 of the protein. When 5-azacytidine-revertant cell lines were selected for resistance to alpha-difluoromethylornithine, the resulting amplified ODC gene was structurally indistinguishable from the wild type gene. These results suggested the existence of a single active ODC locus in CHO cells. Using the methylation-sensitive restriction endonucleases AvaI and HpaII, we found evidence for two differentially methylated alleles in wild type, ODC-deficient and alpha-difluoromethylornithine-resistant cells. One of the alleles appeared completely inactivated by hypermethylation but could be reactivated by demethylation in spontaneous or 5-azacytidine-induced revertants.     

Mutation induction in Escherichia coli incubated in the reaction mixture of NADPH-dependent lipid peroxidation of rat-liver microsomes

Experiments were carried out to examine mutation induction in E. coli cells incubated in the reaction mixture of NADPH-dependent lipid peroxidation of microsomes isolated from rat liver. The results obtained were as follows: (1) Lipid peroxidation of microsomes occurred extensively on incubation with NADPH and Fe2+. In the E. coli WP2uvrA(pKM101) system, the mutation frequency to streptomycin resistance increased markedly when the cells were incubated in the reaction mixture of microsomal lipid peroxidation. The induced mutation frequencies were dependent on the extent of the lipid peroxidation. (2) It was also found that the mutations were induced at the same rate as in the case of (1) when the cells were added to the microsomal suspensions after the reactions due to the short-lived free radicals had terminated. (3) The cytotoxicity of the lipid peroxidation products was larger in the DNA repair-defective mutant, E. coli SR18 (uvrArecA) than the wild-type strain, SR749. From these results it is concluded that some DNA-damaging and mutagenic substances are indeed produced in the degradation process of peroxidized polyunsaturated fatty acids in liver microsomal lipids.     

Optimized sample preparation for tandem capillary electrophoresis single-stranded conformational polymorphism/ heteroduplex analysis

Here we describe DNA sample preparation methods that allow the rapid, simultaneous generation of both single-stranded conformational polymorphism (SSCP) and heteroduplex DNA elements from a single sample in a single tube, which are suitable for direct injection into a capillary electrophoresis (CE) instrument with excellent sensitivity of genetic mutation detection. The p53 gene was used as a model DNA region for this study, which was performed on a high-throughput MegaBACE 96-capillary array electrophoresis instrument. We found that, contrary to the practice common in slab-gel SSCP analysis, denaturants such as formamide are incompatible with this novel technique because they result in homo- and heteroduplex peak broadening in CE (possibly as a result of incomplete dsDNA re-hybridization) that reduces the peak resolution and hence the sensitivity of mutation detection. We also have found that PCR buffers, which are typically used to suspend samples for slab-gel heteroduplex analysis (HA), but which are less suitable for CE because of the presence of extra salt that reduces the efficiency of electrokinetic injection, may be substituted with a 10 mM Tris-HCI buffer (pH 8.5). The use of this Tris-HCl buffer for sample preparation provides both a high sensitivity of mutation detection by tandem SSCP/HA and high efficiency ofelectrokinetic injection by CE. In a related study (published elsewhere), we have applied this optimized protocol to the screening of a set of 32 mutant DNA samples from p53 exons 7 and 8 and recorded 100% sensitivity of mutation detection for tandem CE-SSCP/HA, whereas each individual method yielded lower sensitivity on its own (93% for SSCP and 75% for HA).     

Human cancer, carcinogenic exposures and mutation spectra

Exposure of mammalian cells to alkylating agents causes transfer of alkyl groups to N- as well as O-atoms of DNA bases. Especially the O-alkylated G and T bases have strong mutagenic properties, since they are capable of mispairing during replication. The mutagenic potential of N-alkylbases is less clear although specific base excision repair (BER) pathways exist which remove those lesions from the DNA. We investigated the relative contribution of N-alkylations to mutation induction at the Hprt gene in cultured Chinese hamster ovary cells (CHO). To this end BER activity in CHO cells was modulated by introduction of an expression vector carrying the rat N-alkylpurine-DNA glycosylase (APDG) gene, which codes for a glycosylase that is able to remove 3-methyladenine and 7-methylguanine from DNA thereby generating apurinic sites. Upon selection of a CHO clone which 10 times overproduced APDG compared to control CHO cells, mutation induction, the mutational spectrum, and cell survival were determined in both cell lines following treatment with methyl methanesulfonate (MMS). The results show that over-expression of APDG renders CHO cells more sensitive for mutation induction as well as cytotoxicity induced by MMS. The involvement of apurinic sites in induction of base pair changes at positions where 3-methyladenine was induced is inferred from the observation that the mutational spectrum of MMS-induced mutations in APDG-CHO cells showed twice as much base pair changes at AT base pairs (33.3%) compared to the spectrum of MMS-induced mutations in CHO-control cells (15.8%).     

OxyR regulon controls lipid peroxidation-mediated oxidative stress in Escherichia coli

Membrane lipid peroxidation processes yield products that may react with DNA and proteins to cause oxidative modifications. The oxyR gene product regulates the expression of enzymes and proteins that are needed for cellular protection against oxidative stress. Upon exposure to tert-butylhydroperoxide (t-BOOH) and 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH), which induce lipid peroxidation in membranes, the Escherichia coli oxyR overexpression mutant was much more resistant to lipid peroxidation-mediated cellular damage, when compared to the OxyR deletion mutant in regard to growth kinetics, viability, and DNA damage. The deletion of the OxyR gene in E. coli also resulted in increased susceptibility of superoxide dismutase to lipid peroxidation-mediated inactivation. The results indicate that the peroxidation of lipid is probably one of the important intermediary events in free radical-induced cellular damage. Also, the oxyR regulon plays an important protective role in lipid peroxidation-mediated cellular damage.