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41.
Does the use of DM-nitrophen,nitr-5, or diazo-2 interfere with the measurement of indo-1 fluorescence? 总被引:1,自引:0,他引:1 下载免费PDF全文
Emission spectra of the photolabile Ca2+ chelators DM-nitrophen, nitr-5, and diazo-2 were studied alone, and in the presence of indo-1, to investigate potential interactions that would make the simultaneous manipulation and ratiometric measurement of the intracellular Ca2+ concentration difficult. Neither diazo-2 nor its photoproduct were found to be significantly fluorescent, and consequently concentrations of diazo-2 up to 20 times that of indo-1 did not distort the emission spectra of indo-1. DM-nitrophen was scarcely fluorescent, but its fluorescence did increase upon photolysis. In contrast to diazo-2 and DM-nitrophen, nitr-5 itself was found to be quite fluorescent, and this fluorescence was significantly increased upon photolysis. Thus, combined use of nitr-5 and indo-1 poses the most difficulty. The emission spectra of all the investigated compounds were used to define experimental conditions and calibration procedures that make possible simultaneous measurement and manipulation of the intracellular Ca2+ concentration. 相似文献
42.
Piotr Berman Paul Bertone Bhaskar Dasgupta Mark Gerstein Ming-Yang Kao Michael Snyder 《Journal of computational biology》2004,11(4):766-785
In this paper, we consider several variations of the following basic tiling problem: given a sequence of real numbers with two size-bound parameters, we want to find a set of tiles of maximum total weight such that each tiles satisfies the size bounds. A solution to this problem is important to a number of computational biology applications such as selecting genomic DNA fragments for PCR-based amplicon microarrays and performing homology searches with long sequence queries. Our goal is to design efficient algorithms with linear or near-linear time and space in the normal range of parameter values for these problems. For this purpose, we first discuss the solution to a basic online interval maximum problem via a sliding-window approach and show how to use this solution in a nontrivial manner for many of the tiling problems introduced. We also discuss NP-hardness results and approximation algorithms for generalizing our basic tiling problem to higher dimensions. Finally, computational results from applying our tiling algorithms to genomic sequences of five model eukaryotes are reported. 相似文献
43.
Localization and interaction of the cis-acting elements for abscisic acid, VIVIPAROUS1, and light activation of the C1 gene of maize. 总被引:12,自引:3,他引:9 下载免费PDF全文
The C1 regulatory gene of the maize anthocyanin pathway is regulated by a combination of developmental and environmental signals that include the Viviparous1 (Vp1) gene, abscisic acid (ABA), and light. Using protoplast electroporation and particle bombardment assays, we have defined c/s-acting elements that are necessary and sufficient for the activation of C1 by ABA, VP1, and light, respectively. The sequence from positions -142 to -132 (CGTCCATGCAT) is essential for VP1 activation, whereas a larger overlapping element from -147 to -132 (CGTGTCGTCCATGCAT) is necessary and sufficient for activation by ABA. A separate light (blue and red)-responsive c/s element is located between positions -116 and -59. Light interacts synergistically with the ABA and VP1 responses in transient expression assays, suggesting that combinatorial interaction between modules plays a role in integrating these signals in the developing seed. 相似文献
44.
45.
Denise D. Beusen Janusz Zabrocki Urszula Slomczynska Richard D. Head Jeff L.-F. Kao Garland R. Marshall 《Biopolymers》1995,36(2):181-200
Potent, cyclic hexapeptide analogues of somatostatin are generally believed to adopt some common secondary structural features: a II′ β turn at one end of the cycle, and a type VI turn with a cis amide bond at the other. A proposed cis amide surrogate, the 1,5-disubstituted tetrazole, has been placed into a cyclic hexapeptide analog of somatostatin in order to constrain the putative cis amide bond. The final cyclization was done by either chemical or enzymatic means. The product, cyclo(Ala6-Tyr7-D -Trp8-Lys9-Val10-Phe11-Ψ[CN4]), was found to have 83% of the activity of somatostatin. Solution nmr analysis in DMSO/water revealed that the backbone as well as side chain χ1 and χ2 were well ordered. Relaxation matrix methods were used to extract distance restraints from the nuclear Overhauser effect spectroscopy data set, and these were used in a systematic search of torsional space to identify structures consistent with the nmr data. Restrained minimizations of these structures using a number of different force fields produced structures having the expected βII′ turn at D -Trp8-Lys9 and αβVIa turn in the Phe11-Ψ[CN4]-Ala6 portion of the molecule. The similarity of the minimized structures to those previously reported for cyclic hexapeptide analogues of somatostatin confirms the similarity of the tetrazole geometry to that of the cis amide in solution. © 1995 John Wiley & Sons, Inc. 相似文献
46.
Lipase from Candida rugosa (EC 3.1.1.3) lost only 15% of its activity when held in supercritical CO and about 10% activity in both supercritical SF and hexane even after two days of incubation at up to 60°C and 82 atm.A pressure of 680 atm resulted in up to 15% loss of enzyme activity in supercritical CO and only about 5% loss of activity in supercritical SF 6 even at 410 atm. There was about 60% decrease in enzyme activity even at 1% water content in supercritical CO . Supercritical SF is a better solvent than supercritical CO and hexane. 相似文献
47.
Stereoselectivity of the Chinese hamster ovary cell sialidase: sialoside hydrolysis with overall retention of configuration 总被引:1,自引:1,他引:0
The stereochemical course of enzymatic hydrolysis by the solublesialidase from Chinese hamster ovary cells, expressed as a recombinantprotein in insect Sf9 cells, was determined using proton nuclearmagnetic resonance spectroscopy. 4-Methyl umbelliferyl-N-acetylneuraminic acid was employed as substrate, and the stereoselectivityof the enzyme catalysis was ascertained by monitoring the H3axial and equatorial protons of the sialic acid product overthe reaction course. At both high (3 U) and low concentrations(1 U) of the enzyme, the alpha anomer of the sialic acid wasclearly observed as the initial reaction product. The correspondingbeta anomer of sialic acid appeared much later in the reaction,arising from mutarotation of the alpha anomer. Similar studieswere also carried out using the Salmonella typhimurium LT 2sialidase, a protein of similar size and substrate specificity.Both enzymes apparently cleave the alpha linked sialoside substratewith retention of configuration. Based on the observations ofa wide variety of other glycohydrolytic enzymes that have showna strong correlation of the stereoselectivity of catalysis withactive site topology (Gebler et al, J. Biol. Chem. 267, 1255912561,1992), the results obtained here suggest that the microbialand mammalian sialidases have a homologous active site architectureeven though the molecules do not share significant primary sequencesimilarities. sialidase NMR enzyme mechanism Chinese hamster 相似文献
48.
While globin genes ctt-2β and ctt-9.1 in Chironomus thummi thummi each have a single intron, all of the other insect globin genes reported so far are intronless. We analyzed four globin genes
linked to the two intron-bearing genes in C. th. thummi. Three have a single intron at the same position as ctt-2β and ctt-9.1; the fourth is intronless and lies between intron bearing genes. Finally, in addition to its intron, one gene (ctt-13RT) was recently interrupted by retrotransposition. Phylogenetic analyses show that the six genes in C. th. thummi share common ancestry with five globin genes in the distantly related species C. tentans, and that a 5-gene ancestral cluster predates the divergence of the two species. One gene in the ancestral cluster gave rise
to ctn-ORFB in C. tentans, and duplicated in C. th. thummi to create ctt-11 and ctt-12. From parsimonious calculations of evolutionary distances since speciation, ctt-11, ctt-12, and ctn-ORFB evolved rapidly, while ctn-ORFE in C. tentans evolved slowly compared to other globin genes in the clusters. While these four globins are under selective pressure, we
suggest that most chironomid globin genes were not selected for their unique function. Instead, we propose that high gene
copy number itself was selected because conditions favored organisms that could synthesize more hemoglobin. High gene copy
number selection to produce more of a useful product may be the basis of forming multigene families, all of whose members
initially accumulate neutral substitutions while retaining essential function. Maintenance of a large family of globin genes
not only ensured high levels of hemoglobin production, but may have facilitated the extensive divergence of chironomids into
as many as 5000 species.
Received: 31 December 1996 / Accepted: 16 May 1997 相似文献
49.
脱落酸对线粒体Na^+—K^+ATPase活性的影响 总被引:3,自引:0,他引:3
在提取大豆(Glycine m ax)黄化子叶的线粒体时,于清洗和悬浮介质中加入ABA,发现40 μm ol/L(±) ABA 对线粒体膜结合Na+ -K+ ATPase 活性及线粒体吸氧速率有明显的促进作用。ABA 可使16℃与27℃培养的大豆子叶线粒体膜结合Na+ -K+ ATPase Arrhenius图的折点温度分别下降6.3℃和5.9℃,并将该酶的底物动力学曲线由正协同曲线转变为非协同曲线。表明ABA 可降低线粒体的膜相变温度 相似文献
50.
A serotype-specific epitope of dengue virus 1 identified by phage displayed random peptide library 总被引:3,自引:0,他引:3
Zhi-Jian Yao Mandy C.C. Kao Kean-Chong Loh Maxey C.M. Chung 《FEMS microbiology letters》1995,127(1-2):93-98
Abstract From a panel of monoclonal antibodies of dengue viruses, a serotype-specific epitope of dengue virus 1 was screened from a random peptide library displayed on phage. The epitope was the determinant reactive with monoclonal antibody 15F3-1 that was specific to dengue 1. The screening was monitored by a dot blotting procedure, and after three rounds of screening a consensus motif, HRYSWK, was found. This sequence matches the sequence HKYSWK, corresponding to the amino acid residues 885–890 of polyprotein or residues 111–116 of the non-structural protein 1 of dengue virus serotype 1. The linear epitope was confirmed by testing the antigenicity of chemically synthesized 8-branched peptide. 相似文献