吡喃糖氧化酶电极对葡萄糖和木糖的响应特征

采用戊二醛交联方法,将葡萄糖氧化酶(GOD)和吡喃糖氧化酶分别固定在醋酸纤维素载体膜上,制备电流型电化学酶电极。在SBA双电极分析仪器上安装葡萄糖氧化酶电极和吡喃氧化糖氧化酶电极,分别对不同浓度的葡萄糖、木糖及葡萄糖木糖混合样品进行测试,以葡萄糖氧化酶电极为对照,研究吡喃糖氧化酶电极对葡萄糖、木糖的响应特征。结果表明,吡喃糖酶电极对葡萄糖和木糖都具有良好的响应特征。葡萄糖测定的精密度（RSD）为1.10%（n=10）,在10~1 000 mg/L范围内有良好的线性相关性（R=0.999 0）;木糖测定的RSD为0.80%（n=10）,在10~1 600 mg/L范围内有较好的线性相关性（R=0.999 8）;在葡萄糖木糖混合液测定时,吡喃糖氧化酶电极呈现明显的双底物催化特征,在一定的浓度范围内,对葡萄糖和木糖的响应具有线性相关性。     

Pyridoxine application enhances nitrate reductase activity and productivity ofVigna radiata

Summary Pyridoxine, applied to seeds before sowing or by the spraying of a standing crop of moong (Vigna radiata) significantly enhanced leaf nitrate reductase activity (NRA). Leaf NRA levels, being significantly correlated with seed yield, can be utilized for predicting crop productivity and for adopting corrective measures, if necessary, at an early growth stage.Acknowledgment. This work was partly supported by the award of a Research Fellowship to S.A.A. by the Government of India Council of Scientific and Industrial Research, New Delhi, which is gratefully acknowledged.     

Structure and function of eukaryotic NAD(P)H:nitrate reductase

Pyridine nucleotide-dependent nitrate reductases (NRs; EC 1.6.6.1–3) are molybdenum-containing enzymes found in eukaryotic organisms which assimilate nitrate. NR is a homodimer with an ∼100 kDa polypeptide which folds into stable domains housing each of the enzyme's redox cofactors—FAD, heme-Fe molybdopterin (Mo-MPT) and the electron donor NAD(P)H—and there is also a domain for the dimer interface. NR has two active sites: the nitrate-reducing Mo-containing active site and the pyridine nucleotide active site formed between the FAD and NAD(P)H domains. The major barriers to defining the mechanism of catalysis for NR are obtaining the detailed three-dimensional structures for oxidized and reduced enzyme and more in-depth analysis of electron transfer rates in holo-NR. Recombinant expression of holo-NR and its fragments, including site-directed mutagenesis of key acative site and domain interface residues, are expected to make large contributions to this effort to understand the catalytic mechanism of NR.     

The coordination and function of the redox centres of the membrane-bound nitrate reductases

Under anaerobic conditions and in the presence of nitrate, the facultative anaerobe Escherichia coli synthesises an electron-transport chain comprising a primary dehydrogenase and the terminal membrane-bound nitrate reductase A (NarGHI). This review focuses on recent advances obtained on the structure and function of the three protein subunits of membrane-bound nitrate reductases. We discuss a global architecture for the Mo-bisMGD-containing subunit (NarG) and a coordination model for the four [Fe–S] centres of the electron-transfer subunit (NarH) and for the two b-type haems of the anchor subunit NarI.     

The potential therapeutic role of statins in central nervous system autoimmune disorders

3-Hydroxy-3-methyglutaryl coenzyme A (HMG-CoA) reductase inhibitors, statins are widely used oral cholesterol-lowering drugs. Statins competitively inhibit HMG-CoA reductase, the enzyme that catalyzes conversion of HMG-CoA to L-mevalonate, a key intermediate in cholesterol synthesis. Certain metabolites of mevalonate are also involved in posttranslational modification of specific proteins involved in cell proliferation and differentiation. Thus, statins have important biologic effects that may be independent of their cholesterol-reducing properties. Recent studies indicate that statins have antiinflammatory and neuroprotective properties which may be beneficial in the treatment of multiple sclerosis as well as other central nervous system (CNS) neurodegenerative diseases. This article will outline current experimental evidence that may suggest potential clinical benefits for patients with CNS autoimmune disorders. Ultimately, clinical trials will have to determine the safety and efficacy of statins in this patient population.Received 17 April 2003; received after revision 21 May 2003; accepted 22 May 2003     

镉对黑藻叶光化学及硝酸还原酶特性的影响

研究了不同浓度Cd^2 对黑藻（Hydrilla verticilla(L.f.)Royle）叶光化学及硝酸还原酶特性的影响。结果表明：随着Cd^2 浓度的增加，黑藻叶片的叶绿素含量、叶绿素a和b比值、PSⅠ、PSⅡ及全电子链的活性皆呈现下降的趋势；而其叶绿体ATP的含量、硝酸还原酶的活性、类囊体膜的室温吸收光谱和室温荧光发射光谱则呈现先上升后下降的趋势。实验表明：可根据黑藻叶光化学及硝酸还原酶特性的变化来监测环境中镉污染的程度。     

玉米芯半纤维素常压酸水解技术的研究

玉米芯酸水解技术是生产木糖水解液的关键。实验中,将15％的硫酸喷洒至粉碎玉米芯的表面,浸润一段时间,用90～100℃的蒸汽进行水解,用固液萃取法制得半纤维素水解液。实验表明采用三级逆向连续萃取,半纤维素水解液还原糖的浓度已达13.26％。