Localization of the enzymes involved in H2 and formate metabolism inSyntrophospora bryantii

Cell-free extracts of crotonate-grown cells of the syntrophic butyrate-oxidizing bacteriumSyntrophospora bryantii contained high hydrogenase activities (8.5–75.8 µmol · min^–1 mg^–1 protein) and relatively low formate dehydrogenase activities (0.04–0.07 µmol · min^–1 mg^–1 protein). The K _M value and threshold value of the hydrogenase for H₂ were 0.21 mM and 18 µM, respectively, whereas the K _M value and threshold value of the formate dehydrogenase for formate were 0.22 mM and 10 µM, respectively. Hydrogenase, butyryl-CoA dehydrogenase and 3-OH-butyryl-CoA dehydrogenase were detected in the cytoplasmic fraction. Formate dehydrogenase and CO₂ reductase were membrane-bound, likely located at the outer aspect of the cytoplasmic membrane. Results suggest that during syntrophic butyrate oxidation H₂ is formed intracellularly while formate is formed at the outside of the cell.     

Crystallization,molecular replacement solution,and refinement of tetrameric β-amylase from sweet potato

Sweet potato β-amylase is a tetramer of identical subunits, which are arranged to exhibit 222 molecular symmetry. Its subunit consists of 498 amino acid residues (Mr 55,880). It has been crystallized at room temperature using polyethylene glycol 1500 as precipitant. The crystals, growing to dimensions of 0.4 mm × 0.4 mm × 1.0 mm within 2 weeks, belong to the tetragonal space group P4₂2₁2 with unit cell dimensions of a = b = 129.63 Å and c = 68.42 Å. The asymmetric unit contains 1 subunit of β-amylase, with a crystal volume per protein mass (V_M) of 2.57 ų/Da and a solvent content of 52% by volume. The three-dimensional structure of the tetrameric β-amylase from sweet potato has been determined by molecular replacement methods using the monomeric structure of soybean enzyme as the starting model. The refined subunit model contains 3,863 nonhydrogen protein atoms (488 amino acid residues) and 319 water oxygen atoms. The current R-value is 20.3% for data in the resolution range of 8–2.3 Å (with 2 σ cut-off) with good stereochemistry. The subunit structure of sweet potato β-amylase (crystallized in the absence of α-cyclodextrin) is very similar to that of soybean β-amylase (complexed with α-cyclodextrin). The root-mean-square (RMS) difference for 487 equivalent Cα atoms of the two β-amylases is 0.96 Å. Each subunit of sweet potato β-amylase is composed of a large (α/β)₈ core domain, a small one made up of three long loops [L3 (residues 91–150), LA (residues 183–258), and L5 (residues 300–327)], and a long C-terminal loop formed by residues 445–493. Conserved Glu 187, believed to play an important role in catalysis, is located at the cleft between the (α/β)₈ barrel core and a small domain made up of three long loops (L3, L4, and L5). Conserved Cys 96, important in the inactivation of enzyme activity by sulfhydryl reagents, is located at the entrance of the (α/β)₈ barrel. © 1995 Wiley-Liss, Inc.     

IL－6受体结构与功能的研究进展

ＩＬ－６是一个多功能的细胞因子,其生物学作用在很大程度上受ＩＬ－６受体（ＩＬ－６Ｒ）结构和功能的影响。ＩＬ－６Ｒ由两条多肽链组成,即配体结合链ｇｐ８０和信号传导链ｇｐ１３０。它们在结构和功能上既有分工又有合作。两种亚基组成的高和力ＩＬ－６Ｒ是介导细胞效应所必需的。ＩＬ－６Ｒα中的造血功能区属于造血因子受体超家族成员,它决定着结合ＩＬ－６的能力,然而ｇｐ１３０则是多种细胞因子共用的信号传递分子,其胞     

四川自贡大山铺蜀龙动物群——简报Ⅲ.蜥脚类

本文记述了中侏罗世蜥脚类一新属种——巴山酋龙(Datousaurus bashanensts gen. et sp. nov.)对李氏蜀龙(Shunosaurus lii)的特征进行了补充,讨论了它们在蜥脚类进化过程中的位置。     

子莲新品种‘武植子莲1号’和‘武植子莲2号’产量与营养品质分析

对子莲（Nelumbo nucifera Gaertn.）新品种‘武植子莲1号’和‘武植子莲2号’与其他12个主栽子莲品种的莲子产量和品质性状进行分析,并通过隶属函数分析法对他们的营养品质性状进行综合评价。结果显示：不同子莲品种的产量和营养品质性状差异显著,同一品种在不同发育时期莲子的可溶性糖和淀粉含量等营养指标差异较大;鲜莲子的可溶性糖含量显著高于成熟莲子,而蛋白质和淀粉含量显著低于成熟莲子。与12个主栽子莲品种相比,‘武植子莲1号’在产量上较为突出,成熟莲子的淀粉含量达52.15%,是生产天然淀粉的优良品种;‘武植子莲2号’鲜莲子的直链淀粉和支链淀粉含量低,可溶性糖含量达23.43%,适合鲜食。隶属函数分析结果表明,‘武植子莲1号’和‘武植子莲2号’的综合营养品质较好,具有很高的应用价值。     

月腺大戟根中乙酰基间苯三酚衍生物

从月腺大戟（Euphorbia ebracteolata Hayata)根中分离出一种新的二苯甲烷化合物－双去甲基伪绵马素－AA和2,4－二羟基－6－甲氧基－3－甲基苯乙酮,并用光谱和化学方法确定前者的结构为3,3－二乙酰基－4,4－二甲氧基－2。25,6－四羟基二苯甲烷     

Evidence for an arginine residue at the substrate binding site of Escherichia coli adenylosuccinate synthetase as studied by chemical modification and site-directed mutagenesis

Chemical modification of adenylosuccinate synthetase from Escherichia coli with phenylglyoxal resulted in an inhibition of enzyme activity with a second-order rate constant of 13.6 M-1 min-1. The substrates, GTP or IMP, partially protected the enzyme against inactivation by the chemical modification. The other substrate, aspartate, had no such effect even at a high concentration. In the presence of both IMP and GTP during the modification, nearly complete protection of the enzyme against inactivation was observed. Stoichiometry studies with [7-14C]phenylglyoxal showed that only 1 reactive arginine residue was modified by the chemical reagent and that this arginine residue could be shielded by GTP and IMP. Sequence analysis of tryptic peptides indicated that Arg147 is the site of phenylglyoxal chemical modification. This arginine has been changed to leucine by site-directed mutagenesis. The mutant enzyme (R147L) showed increased Michaelis constants for IMP and GTP relative to the wild-type system, whereas the Km for aspartate exhibited a modest decrease as compared with the native enzyme. In addition, kcat of the R147L mutant decreased by a factor of 1.3 x 10(4). On the bases of these observations, it is suggested that Arg147 is critical for enzyme catalysis.