The effect of oxidants on biomembranes and cellular metabolism

During the reductive process in the tissues, the aerobes generate a number of oxidants. Unless these oxidants are reduced, oxidative damage and cell death would occur. Oxidation of plasma membrane lipids leads to autocatalytic chain reactions which eventually alter the permeability of the cell. The role of oxidative damage in the pathophysiology of diabetic complications and ischemic reperfusion injury of myocardium, especially the changes in the channel activity which may lead to arrhythmia have been studied. Hyperglycemia activates aldose reductase which could efficiently reduce glucose to sorbitol in the presence of NADPH. Since NADPH is also aldose required by glutathione reductase for reducing oxidants, its diversion would lead to membrane lipid oxidation and permeability changes which are probably responsible for diabetic complications such as cataractogenesis, retinopathy, neuropathy etc. Antioxidants such as butylated hydroxy toluene (BHT) and also reductase inhibitors prevent or delay some of these complications. By using patch-clamp technique in isolated frog myocytes, we have shown that hydroxy radicals generated by ferrous sulfate and ascorbate as well as lipid peroxides such as t-butyl hydroperoxide facilitate the entry of Na⁺ by oxidizing Na⁺-channels. Increased intracellular Na⁺ leads to an increase in Na⁺/Ca²⁺ exchange. The increased Na⁺ concentration by itself may produce electrical disturbance which would result in arrhythmia. Increased Ca²⁺ may affect proteases and may help in the conversion of xanthine dehydrogenase to xanthine oxidase, consequently increased production of super oxide radicals. Increased membrane lipid peroxidation and other oxygen free-radical associated membrane damage in myocytes has been demonstrated.     

Structure of DNA hydration shells studied by Raman spectroscopy

We have used Raman scattering to study the water O-H stretching modes at approximately 3450 and approximately 3220 cm-1 in DNA films as a function of relative humidity (r.h.). The intensity of the 3220-cm-1 band vanishes as the r.h. is decreased from 98% to around 80%, which indicates that the hydrogen-bond network of water is disrupted in the primary hydration shell (which therefore cannot have an "ice-like" structure). The number of water molecules in the primary hydration shell was determined from the intensity of the approximately 3200-cm-1 band as about 30 water molecules per nucleotide pair. The approximately 3400-cm-1 O-H stretch band was used for determining the total water content, and this band persists at 0% r.h., implying that 5-6 tightly bound water molecules per nucleotide pair remain. The frequency of the approximately 3400-cm-1 O-H stretch mode is lower by 30 to 45 cm-1 in the primary hydration shell compared to free water. The water content as a function of r.h. obtained from these experiments agrees with gravimetric measurements. The disappearance of the approximately 3200-cm-1 band and the shift of the approximately 3400-cm-1 O-H stretch band provide a reliable way of measuring the hydration number of DNA.     

Oligosaccharide synthesis by enzymatic transglycosylation

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用体外免疫法建立人—人抗流行性乙型脑炎病毒杂交瘤细胞株

利用单克隆抗体(McAb)进行病毒病的治疗是人们所关心的一个重大课题。 流行性乙型脑炎(乙脑)是一种严重威胁人民健康的急性传染病,病死率高,后遗症严重。国内外目前尚无特效疗法。陈伯权等用乙脑病毒皮下或腹腔感染3周龄小白鼠24、48小时及5天后,分别用乙脑病毒51-8McAb进行治疗,平均治愈率分别为78％、73％及22％。     

马铃薯Y病毒外壳蛋白基因的克隆及序列分析

本文报道应用聚合酶链式反应(PCR)技术,在体外扩增马铃薯 Y 病毒外壳蛋白基因及其克隆和序列分析的结果。病毒 RNA 从马铃薯 Y 病毒感染的烟草叶片中提取,用合成的PCR 3引物及 AMV 逆转录酶合成了单链的 cDNA。利用 PCR 技术,经30个循玎的扩增。得到了一特异的0.8kb 片段。克隆后对此片段进行了限制性内切酶物理图谱分析,并测定了其全序列。实验结果证明,我们克隆到的是完整的马铃薯 Y 病毒的外壳蛋白基因。与国外报道的马铃薯 Y 病毒 N 株相比,其核苷酸序列及推测的氨基酸序列的同源率分别为97.8%和97%。将该基因导入马铃薯以期获得抗 Y 病毒马铃薯的工作正在进行。本文还对 PCR 技术用于扩增植物 RNA 病毒的方法以及用基因工程方法培育抗病毒作物新品种的可行性等进行了讨论。     

Polymerase chain reaction (PCR) techniques for site-directed mutagenesis

Polymerase chain reaction (PCR) technology has revolutionized the process of isolating and amplifying segments of DNA. One powerful application of PCR is its use in precise site-directed mutagenesis (SDM). SDM provides an elegant tool for scientists and engineers to explore biocatalytic mechanisms and processes to understand the structural-functional relationships of enzymes and other proteins. This article reviews techniques and methodology used in site-directed mutagenesis of genes by PCR.     

Germin-Like Polypeptides Increase in Barley Roots during Salt Stress

The 26 kilodalton, isoelectric point 6.3 and 6.5 (Gs1 and Gs2) polypeptides that increase in barley (Hordeum vulgare L.) roots during salt stress were isolated and identified. Both Gs1 and Gs2 had high sequence similarity to germin, a protein that increases significantly in germinating wheat seeds. Like germin, Gs1 and Gs2 were resistant to proteases and were glycosylated. Immunoblots were probed with antibodies to Gs1 and Gs2 to determine the distribution of these polypeptides among organs and cell-free fractions. Gs1 and Gs2 were present in roots and coleoptiles, but absent from leaves. In roots, Gs1 and Gs2 were present in the mature region, but not the tip. Gs1 and Gs2 increased in roots, but decreased in coleoptiles in response to salt stress. Gs1 and Gs2 were distributed among the soluble, microsomal, and cell wall fractions of roots, but the majority of Gs1 and Gs2 was present in the soluble fraction. Although Gs1 and Gs2 were heat stable, their synthesis was not affected by abscisic acid treatment. Gs2 accumulated during abscisic acid treatment, whereas Gs1 did not. However, a 25.5 kilodalton, isoelectric point 6.1 polypeptide that was immunologically related to Gs1 did accumulate with abscisic acid treatment.     

西双版纳傣族“龙山”的生态学意义

傣族“龙山”是西双版纳地区傣族的民族植物文化中的一例。其概念是“神居住的地方”,在这个地方的动植物都是神的家园里的生灵,是神的伴侣,是不能砍伐、狩猎和破坏的。人