东海原甲藻和链状亚历山大藻对硝酸盐和氨盐的生理响应

比较研究了硝酸盐和氨盐培养下,两种甲藻(东海原甲藻(Prorocentrum donghaiense Lu)和链状亚历山大藻(Alexandriumcatenella DH01))对氮营养盐的生理响应.结果表明,两种赤潮生物的最大比增长率均随着培养液中硝酸盐浓度的升高(20～80μmol/L)而增加,且硝酸盐培养下的最大比增长速率高于同浓度的氨盐,表明在高浓度下,硝酸盐是适宜的氮源.东海原甲藻硝酸还原酶活力(1.14～5.20 fmol/(cell.L.min))与硝酸盐吸收速率呈正相关,链状亚历山大藻中则未检测到硝酸还原酶活力;两种赤潮生物谷酰氨合成酶活力对硝酸盐和氨盐的响应存在差异,链状亚历山大藻谷氨酰胺合成酶活力(10.93～30.97 pmol/(cell.L.min))要远高于东海原甲藻(0.34～0.95 pmol/(cell.L.min)).两种赤潮生物对硝酸盐和氨盐的不同生理响应可能是引起赤潮期间种群更替的一个重要原因.     

小麦谷氨酰胺合成酶(GS)的器官分布及光照对GS基因表达的影响

用组织印迹法、Northern分子杂交、DEAE-纤维素柱层析技术、酶活性测定以及抑制剂等研究了小麦幼苗各器官谷氨酰胺合成酶(GS)活性的变化和光对GS活性及GS-mRNA的影响。结果表明:小麦幼苗各器官的GS活性和特性是不一样的。PPT对绿叶中GS的抑制高于根部,对叶绿体谷氨酰胺合成酶(GS2)的抑制强于细胞质谷氨酰胺合成酶(GSI)。组织印迹杂交测定了小麦汁液GS-mRNA的器官组织专一性基因的表达。光对总RNA和GS-mRNA有明显的诱导作用。     

固氮鱼腥藻_AnabaenaazoticaHB686_谷氨酰胺合成酶的生化特性

固氨鱼腥藻HB686谷氨酰胺合成酶(GS)具有Mg~(2 )-依赖的生物合成活性和Mn~(2 )-依赖的γ-谷氨酰基转移酶活性.生物合成活性对ATP、谷氨酸和氯化铵有较强的亲和力,其Km值分别为0.80mM、0.48mM和0.68mM.γ-谷氨酰基转移酶对谷氨酰胺和羟氨的Km值分别为2.0mM和0.9mM.作者研究了pH和温度对谷氨酰胺合成酶活性的影响,发现蛋氨酸亚砜、尿素、铵离子、天冬氨酸和甘氨酸对谷氨酰胺合成酶均表现出不同程度的抑制作用.某些金属离子对维持谷氨酰胺合成酶的稳定有一定的作用.     

水质净化微生物絮凝剂研究进展

微生物絮凝剂是近年来研究的新型水处理剂．本文从菌种选育、絮凝特性、结构、应用、合成酶等几个方面,综述了国内外最新研究成果．最后,展望了微生物絮凝剂的研究发展方向．     

S-腺苷甲硫氨酸合成酶的可溶性表达

系统考察了pET可溶性表达系统对酵母来源的S-腺苷甲硫氨酸(SAM)合成酶基因的表达情况,结果显示:当采用含Nus.Tag融合标签的pET-44a为载体,trxB和gor双突变的Ori-gami为宿主时最适合目的蛋白的可溶性表达。进一步考察不同来源(大肠杆菌、枯草芽孢杆菌、苏云金芽孢杆菌)SAM合成酶的可溶性时,也得到了相似的结论;比较发现酵母来源的SAM合成酶可溶性表达的比活力最高达60.9U/mg。     

牛体外受精卵发育培养条件的研究

将采自屠宰母牛卵巢的未成熟卵子在含有促进性腺激素和胎牛血清的TCM199培养基内培养成熟后,使用以钙离子载体Ionophore A23187诱导获能的牛精子进行授精处理.在受精卵发育用培养基中添加了谷氨酰胺,并以此与无添对照进行了对比,探索了培养基内谷氨酰胺的存在与否对胚胎发育的影响.另外,在发育用培养基内还分别添加了胎牛血清(FCS),阉牛血清(NSS)以及发情母牛血清(OCS)以观察其培养效果,结果表明,谷氨酰胺对胚胎的发育有极大的促进作用,添加谷氨酰胺的处理组与对照组中发育为桑椹胚、囊胚的胚胎比例分别为23.4%和6.6%,具有极显著的整异.而在含有FCS、NSS和OCS的TCM199培养基内培养的卵子中分别有81.4%,70.7%和82.9%发育为二细胞期胚胎,将胚胎继续培养至授精后第8天时,三个处理组中发育为桑椹胚、囊胚的胚胎比例分别为30.0%,40.2%和47.1%,以OCS的培养效果为最佳.本研究的结果证明,谷氨酰胺和发情母牛血清对牛体外受精卵的体外发育具有良好的促进作用.     

Structure-function relationships in methionine adenosyltransferases

Methionine adenosyltransferases (MATs) are the family of enzymes that synthesize the main biological methyl donor, S-adenosylmethionine. The high sequence conservation among catalytic subunits from bacteria and eukarya preserves key residues that control activity and oligomerization, which is reflected in the protein structure. However, structural differences among complexes with substrates and products have led to proposals of several reaction mechanisms. In parallel, folding studies begin to explain how the three intertwined domains of the catalytic subunit are produced, and to highlight the importance of certain intermediates in attaining the active final conformation. This review analyzes the available structural data and proposes a consensus interpretation that facilitates an understanding of the pathological problems derived from impairment of MAT function. In addition, new research opportunities directed toward clarification of aspects that remain obscure are also identified. Received 22 August 2008; received after revision 22 September 2008; accepted 26 September 2008     

2’-5’ Oligoadenylate synthetase shares active site architecture with the archaeal CCA-adding enzyme

The 2'-5' oligoadenylate synthetases (OAS) are interferon-induced antiviral enzymes that recognise virally produced dsRNA and initiate an RNA destabilisation within the infected cell. We compared the structure of OAS to that of poly adenosine polymerase (PAP) and the class I CCA-adding enzyme from Archeoglobus fulgidus (AfCCA). This comparison revealed a strong structural homology between the three enzyme families. In particular, the active sites of OAS and CCA class I enzymes are highly conserved. We conducted an extensive mutagenesis of amino acid residues within the putative active site in OAS, thereby identifying enzymatically important residues and confirming the common active site architecture for OAS and the AfCCA. Our findings also have profound implications for our understanding of the evolutionary origin of the OAS enzymes and suggest that the OAS proteins diverged from a common 3'-specific ancestor at the beginning of metazoan evolution.