Bt玉米叶片保护酶活性变化的研究

水培条件下研究转Bt基因玉米(Bt玉米)农大61和1 426×1 482在不同时期保护酶POD,PPO和SOD的活性变化。实验分别在正常生长条件和PEG胁迫下进行。在正常水培条件下,Bt玉米的POD,PPO和SOD的活性一般显著或极显著低于非转基因玉米农大3138;而在PEG胁迫下Bt玉米这些酶的活性却显著或极显著高于非转基因玉米。试验结果说明PEG胁迫下Bt玉米保护酶活性下降幅度较非转基因玉米小,比非转基因玉米具有更强的抗性。     

采后番茄果皮中抗病相关酶活性的诱导

绿熟番茄经2．4kJ/m^2UV-C照射后，果皮中防御酶活性被诱导升高，POD、PPO活性在处理后第2天分别提高1．3和1．13倍，PAL活性在第4天提高1．69倍，几丁质酶活性下降被延缓，β-1，3-葡聚糖酶活性在第2天提高1．3倍，同时贮期自然发病率和人工接种发病率降低。     

壳聚糖对MDMV的防效与玉米叶片防御酶活性的关系

试验以人工摩擦接种法接种MDMV ,以比色法测定了壳聚糖对MDMV侵染的玉米叶片几种防御酶活性的影响 .初步结果表明 ,壳聚糖处理有使酶活提高或使酶峰提前的趋势 .尤其使PO酶活提高明显 ,PPO、PAL、几丁质酶的酶活稍有提高 ,主要表现在处理初期 .壳聚糖诱导抗毒机制似乎与PO有关 ,而与PPO、PAL、几丁质酶无关或相关性不大 .药剂防效试验表明壳聚糖有一定防病效果 .接毒可使玉米叶片可溶性蛋白含量降低 ,但喷壳聚糖后再接毒的蛋白含量变化不大 .这在一定程度上反应出壳聚糖诱导产生的抑制病毒复制的诱导抗病作用 .     

基因功能注释——后基因组时代面临的挑战

在已经解序的、数以百计的生物基因组中,存在大量编码未知功能蛋白的基因序列。同时,众多已知功能的酶蛋白在解序的基因组中找不到对应的基因。确定未知功能基因的功能和寻找孤儿酶对应的基因是后基因组时代面临的极具挑战性的科学任务。本文综合讨论了目前基因组中基因功能注释存在的问题及解决这些问题的策略与方法。     

紫杉醇生物合成途径及其相关酶的研究进展

紫杉醇的生物合成过程已基本阐明,其合成以NB028牛儿基NB028牛儿基二磷酸为前体约需20步酶促反应,近一半的相关酶基因已得到克隆与表达.综述了紫杉醇生物合成及生物合成途径中9个酶基因的克隆和表达方面的研究进展,并指出随着紫杉醇生物合成分子生物学研究的不断深入,利用分子生物技术大规模生产紫杉醇将为期不远.     

淀粉水解酶在食品工业中的应用

淀粉水解酶是指一类能催化水解淀粉酶的总称,不同使用用途及生产目的使用的淀粉水解酶的类别也不相同,本文分别介绍了淀粉水解酶中的α-淀粉酶,β-淀粉酶,异淀粉酶,葡萄糖淀粉酶的作用机理、酶性质以及在食品工业中的应用情况,为生产中淀粉水解酶的应用提供一些参考。     

Synergistic defensive mechanism of phytochelatins and antioxidative enzymes in Brassica chinensis L. against Cd stress

Brassica chinensis L. was chosen and exposed to different concentrations of Cd exposure to evaluate its Cd-accumulating capacity and its potential cellular defensive mechanisms. Cd accumulation in the shoots and roots of B. chinensis was up to 1348.3±461.8 and 3761.0±795.0 mg per killogram of dry weight, respectively, under 200 μmol/L of Cd exposure. Increasing Cd accumulation in the plant was accompanied by rapid accumulation of phytochelatins (PCs), and the sequestration of Cd by PCs provided a primary cellular mechanism for Cd detoxification and tolerance of B. chinensis. Furthermore, malondialdehyde formation, hydrogen peroxide content and antioxidative enzyme activities such as superoxide dismutase, catalase, guaiacol peroxidase and ascorbate peroxidase were observed in the shoots of Cd-stressed B. chinensis. Increasing enzyme activities in response to concentrations of 5 to 50 μmol/L Cd showed an efficient defense against oxidative stress, suggesting that the antioxidative system was a secondary defensive mechanism. These resulted in reduced free Cd damage and enhanced Cd accumulation and tolerance. Glutathione plays a pivotal role in these two detoxification pathways. In general, these results suggested that PCs and the antioxidative system are synergistic in combatting Cd-induced oxidative stress and that they play important roles in Cd detoxification of B. chinensis, and also give a deep understanding of the natural defensive mechanisms in plants under heavy metal stress.     

Tetracyclines inhibit parathyroid hormone-induced bone resorption in organ culture

Summary Several tetracyclines (minocycline, doxycycline, tetracycline), in levels approximating physiologic concentrations, were found to inhibit parathyroid hormone-induced bone resorption in organ culture; the specificity of this effect was demonstrated by comparison with other (non-tetracycline) types of antibiotics. The ability of tetracyclines to inhibit bone resorption is consistent with the recent proposal by Golub et al². that these antibiotics can inhibit mammalian collagenolytic enzymes by a mechanism unrelated to the drug's antibacterial efficacy, a property which could be therapeutically useful in diseases characterized by excessive collagen breakdown.     

温度和pH对驼背鲈消化酶活力的影响

采用酶学分析方法研究了温度和pH对驼背鲈3种主要消化酶(蛋白酶、脂肪酶、淀粉酶)活力的影响。结果表明:在设定的温度和pH范围内,驼背鲈消化酶活力均随着温度和pH的升高呈先升后降的趋势。其中,胃蛋白酶的最适温度为40~45℃,肠、幽门盲囊、肝蛋白酶的最适温度均为40℃;胃脂肪酶的最适温度为35℃,幽门盲囊的最适温度为40~45℃,其他部位均为40℃;胃淀粉酶的最适温度为40℃,其他部位均为35℃。胃蛋白酶的最适pH为3.2,肠、幽门盲囊、肝的最适pH均为8.2;胃、肝脂肪酶的最适pH分别为7.2、8.2,其他部位均为6.2;胃淀粉酶的最适pH为7.2~8.2,其他器官的最适pH均为7.2。各部位在最适温度和pH下,脂肪酶酶活力顺序为肠胃肝幽门盲囊,淀粉酶酶活力顺序为肠幽门盲囊胃肝;蛋白酶在最适温度和pH下的酶活力顺序分别为肠胃肝幽门盲囊、肠胃幽门盲囊肝。