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381.
382.
Romy Fleischer Michael Wiese Reinhard Troschütz Mario Zink 《Journal of molecular modeling》1997,3(8):338-346
Quantitative structure-activity relationships for piritrexim and analogues acting as inhibitors of tumour cell growth have been derived. First the Free-Wilson-method was used on a homologous training set of eight derivatives. The selection of variables important for the biological activity of the compounds was carried out with different multivariate methods as multiple linear regression, the partial least squares method und a genetic algorithm. The derivation of three-dimensional structure activity relationships started with a systematic conformational analysis of all compounds. For the conformations having minimal energy and being in agreement with the crystal structure of piritrexim charges were calculated with the AM1 hamiltonian. For the superimposition of the derivatives two methods were used: maximal similarity of the common substructure or of the molecular fields. A Comparative Molecular Field Analysis with steric and electrostastic fields identified regions important for the activity of the studied compounds independent of the chosen alignment and also correctly predicted the activity of two nonhomologous compounds. 相似文献
383.
Strategic collection planning is a relatively new concept for zoos. Until recently, personal preference, availability, and competition determined which species or subspecies were acquired. In the last few years, however, there have been attempts to employ systematic criteria for taxon selection that better serve conservation objectives. Planning currently occurs at three levels: global, regional, and institutional. The current planning process is reviewed and recommendations are made for ways the process might be improved. An efficient, economical, and effective collection planning process is critical if modern, professionally managed zoological institutions are to make a significant impact on wildlife and ecosystem conservation. Rather than selecting taxa solely on the possibility of a future reintroduction, serious consideration should be given to the ability of a species or subspecies to contribute to more immediate conservation goals, including public education, fund raising to support field conservation, and scientific research. Because resources are limited, perhaps zoos should focus their long-term breeding programs primarily on flagship species—that is, those that have the potential to excite public attention and help to protect habitat and other taxa—rather than on a broad array of species that are currently endangered. © 1995 Wiley-Liss, Inc. 相似文献
384.
In this paper, a statistical model for clinical trials is presented for the special situation that a varying and unstructered number of binary responses is obtained from each subject. The assumptions of the model are the following: 1.) For each subject there is a (constant) individual Bernoulli parameter determining the distribution of the binary responses of this subject. 2.) The Bernoulli parameters associated with the subjects are realizations of independent random variables with distributions Pg in treatment group g(g = 1, 2, …, G). 3.) Given the value of the Bernoulli parameter, the observations are stochastically independent within each subject. Under these assumptions, a test statistic is derived to test the hypothesis H0:E(P1) = E(P2) = … = E(PG). It is proven and demonstrated by simulations, that the test statistic asymptotically (i.e. for a large number of subjects) follows the X2-distribution. 相似文献
385.
386.
387.
The bandwidth of membrane current measurements in potential-clamped Ranvier nodes is limited by the low-pass filter properties of the internodes. If about 35% of the current measuring internode is grounded via an additional electrode, the bandwidth of this internode increases by a factor of about 40. Consequently, in potential clamp experiments the measured time course of the early ionic currents changes markedly, while the duration of the capacity current is shortened. 相似文献
388.
389.
Arnulf Timm Stefan Wiese Alexander Steinbüchel 《Applied microbiology and biotechnology》1994,40(5):669-675
Using a 30-mer oligonucleotide probe highly specific for polyhydroxyalkanoic acid (PHA) synthase genes, the respective genes of Pseudomonas citronellolis, P. mendocina, Pseudomonas sp. DSM 1650 and Pseudomonas sp. GP4BH1 were cloned from genomic libraries in the cosmid pHC79. A 19.5-kbp and a 22.0-kbp EcoRI restriction fragment of P. citronellolis or Pseudomonas sp. DSM 1650, respectively, conferred the ability to accumulate PHA of medium-chain-length 3-hydroxyalkanoic acids (HA
mcl
) from octanoate as well as from gluconate to the PHA-negative mutant P. putida GPp104. An 11.0-kbp EcoRI fragment was cloned from P. mendocina, which restored in GPp104 the ability to synthesize PHA from octanoate but not from gluconate. From Pseudomonas sp. GP4BH1 three different genomic fragments encoding PHA synthases were cloned. This indicated that strain GP4BH1 possesses three different functionally active PHA synthases. Two of these fragments (6.4 kbp and 3.8 kbp) encoded for a PHA synthase, preferentially incorporating hydroxyalkanoic acids of short chain length (HA
scl
), and the synthases were expressed in either GPp104 and Alcaligenes eutrophus H16-PHB–4, respectively. The PHA synthase encoded by the third fragment (6.5 kbp) led to the incorporation of HA
mcl
and was expressed in GPp104 but not in PHB–4.
Correspondence to: A. Steinbüchel 相似文献
390.
A simple preparation of Ac-Arg-(p-TosH or HCl)-NHMe is described. The NG-protonated Z-Arg was coupled with methylamine by the mixed anhydride method. Z-Arg-NHMe was purified as a NG-p-toluene sulfonate salt by crystallization from water. After removal of the Z group by catalytic hydrogenation and acetylation Ac-Arg(p-TosH)-NHMe was obtained. Ac-Arg(HCl)-NHMe was prepared by chromatography of the NG-TosH derivative on Dowex 44 (in Cl- form). 相似文献