海枣曲霉β-半乳糖苷酶的提纯与性质

 通过过聚乙二醇6000-磷酸钾缓冲液双相分离、Sephadex G-100凝胶过滤、DEAE-Sephadex A-50离子交换层析、羟基磷灰石层析及SephadexG-100凝胶过滤等提纯步骤,从海枣曲霉(Aspergillus phoenicis)麦麸培养物抽提液中提纯得到凝胶电泳均一的β-半乳糖苷酶。该酶的最适pH为3.5—4.0,最适温度为60℃(反应15分钟),在pH5.0—8.5之间及60℃以下稳定。在65℃和70℃保温时失活50％的时间分别为27和2分钟。用SDS凝胶电泳法和梯度凝胶电泳法分别测得该酶的分子量为115,000和118,000。薄层凝胶等电聚焦法测得其等电点为pH4.6。     

海枣曲霉β-半乳糖苷酶的催化性质

 通过测定海枣曲霉β-半乳糖苷酶的底物特异性,表明该酶水解对-硝基酚基β-半乳糖苷(PNP-β-gal)的活力最高。该酶水解PNP-β-gal,乳糖和对-硝基酚基β-D-岩藻糖苷(PNP-β-fuc)的相对活力为100,63.1,10.3。不同测定方法的结果均表明,这一PNP-β-fuc水解活性来自β-半乳糖苷酶本身。Hg~(2+)、D-半乳糖和D-半乳糖-r-内酯对该酶有强烈的抑制作用,Ag~+和4mol/l脲也有较强的抑制作用。该酶水解PNP-β-gal和乳糖的Km值分别为1.3及36.2mmol/l,Vmax则分别为478和189μmol.min~(-1).mg~(-1)。Lineweaver-Burk作图法及Dixon作图法均表明D-半乳糖和D-半乳糖酸-γ-内酯对该酶显示竞争性抑制作用,其Ki分别为4和0.9mmol/l。     

中国樟科植物拾零

报道了中国樟科植物的１个新种,２个新组合,１个新异名和２个新分布。     

海枣曲霉木聚糖酶的纯化及末端序列研究

海枣曲霉麸曲经水浸提、硫酸铵盐析、凝胶过滤、离子交换层析及ＨＰＬＣ分子排阻层析制备了ＰＡＧＥ,ＳＤＳ－ＰＡＧＥ、ＰＡＧＥ酶谱及ＨＰＬＣ纯的木聚糖酶。     

海枣曲霉木聚糖酶Ⅲ糖组成及糖肽结合键研究

海枣曲霉木聚糖酶Ⅲ经PAGE和SDS-PAGE后用Schiff’s试剂染色证明为糖蛋白。经硅胶薄层层析和毛细管气相色谱测定,每分子酶约含4个葡萄糖和1个甘露糖残基。 木聚糖酶Ⅲ经β-消除反应后在241nm处出现一个新的吸收峰。在N_2保护下用含NaBH_4的NaOH溶液处理后,其Ser和Thr减少,相对应丙氨酸增加,并出现α-氨基丁酸。估测酶分户中存在约3个O-糖苷键,糖残墓通过O-糖苷键连接于肽链中丝氨酸或苏氨酸上。     

海枣曲霉木聚糖酶降解寡聚木糖的特性

利用滤纸层析或ＡｃｒｙｌｅｘＰ－２凝胶过滤从落叶松木聚糖硫酸水解液中分离纯化子木二糖至木五糖。采用硅胶薄层层析分析底物和产物的方法研究了海枣霉木聚糖酶降解寡聚木糖的特点。此酶作用于寡糖的最适ＰＨ为５．０,终产物为Ｘ和Ｘ２。酶作用于Ｘ３、Ｘ４及Ｘ５的相对初速度分别为１、３４和４００,Ｘ２几乎不被酶解,推断该酶的底物结合部位至少具有５个亚位点,在高底物浓度,低酶量,远离最适ＰＨ以及在反应初期都能检测到     

Do domatia mediate mutualistic interactions between coffee plants and predatory mites?

Many plant species possess structures on their leaves that often harbour predatory or fungivorous mites. These so‐called domatia are thought to mediate a mutualistic interaction; the plant gains protection because mites decimate plant pathogenic fungi or herbivores, whereas the mites find shelter in the domatia. We tested this hypothesis using two species of coffee (Coffea spp.) plants that posses domatia consisting of small cavities at the underside of the leaves, and which often harbour mites. We assessed densities of domatia, of the predatory mite Iphiseiodes zuluagai Denmark and Muma (Acari: Phytoseiidae) and of herbivorous mites Oligonychus ilicis (McGregor) (Acari: Tetranychidae) and Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae) on Coffea arabica L. (Rubiaceae) and Coffea canephora Pierre in the field. Over a period of 50 days, C. arabica harboured on average 7.5 times more predatory mites and 0.4–0.66 fewer prey mites than C. canephora. Hence, the higher density of predatory mites on C. arabica could not be explained by higher densities of prey. However, the density of domatia on C. arabica was on average 1.65 times higher than on C. canephora, and within each species, leaves with higher densities of domatia also harboured more predators. This suggests a positive effect of domatia on predatory mites. In the laboratory, survival of adult female predatory mites on leaves of C. arabica with open domatia was indeed significantly higher than on leaves with closed domatia. Hence, predatory mites benefited from the domatia. However, plants with higher densities of domatia did not harbour fewer herbivores. Taken together, our study only provides partial evidence for a mutualistic interaction between coffee plants and predatory mites, mediated by domatia.     

Purification and properties of a thermostable extracellular β-D-xylosidase produced by a thermotolerant Aspergillus phoenicis

A β-D-xylosidase was purified from cultures of a thermotolerant strain of Aspergillus phoenicis grown on xylan at 45°C. The enzyme was purified to homogeneity by chromatography on DEAE-cellulose and Sephadex G-100. The purified enzyme was a monomer of molecular mass 132 kDa by gel filtration and SDS-PAGE. Treatment with endoglycosidase H resulted in a protein with a molecular mass of 104 kDa. The enzyme was a glycoprotein with 43.5% carbohydrate content and exhibited a pI of 3.7. Optima of temperature and pH were 75°C and 4.0–4.5, respectively. The activity was stable at 60°C and had a K _m of 2.36 mM for p-nitrophenyl-β-D-xylopiranoside. The enzyme did not exhibit xylanase, cellulase, galactosidase or arabinosidase activities. The purified enzyme was active against natural substrates, such as xylobiose and xylotriose. Journal of Industrial Microbiology & Biotechnology (2001) 26, 156–160. Received 23 June 2000/ Accepted in revised form 29 September 2000