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991.
Hydrogen selenide ion (HSe?) has an important role in the metabolism of the essential trace element selenium. Several redox reactions of selenide were found to be dominated by the amount of colloidal elemental selenium (Se°) generated during the reaction. The following reaction of selenide with the disulfide, oxidized glutathione (GSSG), was used as an example: HSe? + GSSG + H+ → Se° + 2 GSH. The resulting thiol is reduced glutathione (GSH; γ-glutamylcysteinylglycine). By following this reaction with polarography, it was seen that the ratio of colloidal selenium produced to selenide unreacted was a constant 2.1 ± 0.1, and was the only factor found to determine the extent of oxidation. This is best explained by the hypothesis that freshly generated colloidal selenium adsorbs selenide readily; no evidence for polyselenide formation was found. Adsorption of selenide should be considered in any reaction involving the oxidation of selenide to colloidal selenium. 相似文献
992.
The room-temperature electronic spectra of the chromium chalcocarbonyl complexes, Cr(CO)5(CX) and (η6-C6H6)Cr(CO)2(CX) (X = O, S, Se), have been recorded in solution, and in some cases, in the gas phase. Assignments for the thiocarbonyl and selenocarbonyl spectra are proposed on the basis of the literature assignments for the parent all-CO derivatives. Overall, the data support the order of increasing electron withdrawing capacity of the chalcocarbonyl ligands as CO < CS < CSe. 相似文献
993.
Luciano Antolini Ledi Menabue Monica Saladini Marco Sola Luigi Pietro Battaglia Anna Bonamartini Corradi 《Inorganica chimica acta》1984,93(2):61-66
Mixed ligand complexes of the type Cu(Z-aminoacidato)2(B2) (Z = benzyloxycarbonyl group, Z-aminoacidate = Z-glycinate (Zgly), Z-alaninate (Zala); Z-valinate (Zval), Z-leucinate (Zleu) ion, B = imidazole (Im), N-methylimidazole (MeIm)) were synthesized and characterized by means of electronic, infrared and EPR spectroscopies. For one of them, bis(Z-alaninato)bis(N-methylimidazole)copper(II) ethanol solvate, the crystal and molecular structure was also determined by the single crystal X-ray diffraction method. The complex crystallizes in the monoclinic space group P21/c, with cell dimensions a = 11.1119(6), b = 18.8398(7), c = 8.9652(5) Å, β = 105.380(2)° and Z = 2. The structure was solved by conventional Patterson and Fourier methods and refined by full-matrix least-squares to an R value of 0.045. The complex has square-planar coordination via two centrosymmetric carboxylic oxygens and two N-methylimidazole nitrogens. The second carboxylate oxygen is 2.731(5) Å from the copper atom in an ‘out of plane’ position. Packing is mainly determined by hydrogen bondings between amide nitrogen and amide carboxyl oxygen. Electronic, infrared and EPR spectra are consistent with this type of coordination geometry for anhydrous complexes, while for hydrate complexes are suggestive of tetragonal bipyramidal geometry. 相似文献
994.
The purpose of this work has been to develop a model of electromyographic (EMG) patterns during single-joint movements based on a version of the equilibrium-point hypothesis, a method for experimental reconstruction of the joint compliant characteristics, the dual-strategy hypothesis, and a kinematic model of movement trajectory. EMG patterns are considered emergent properties of hypothetical control patterns that are equally affected by the control signals and peripheral feedback reflecting actual movement trajectory. A computer model generated the EMG patterns based on simulated movement kinematics and hypothetical control signals derived from the reconstructed joint compliant characteristics. The model predictions have been compared to published recordings of movement kinematics and EMG patterns in a variety of movement conditions, including movements over different distances, at different speeds, against different-known inertial loads, and in conditions of possible unexpected decrease in the inertial load. Changes in task parameters within the model led to simulated EMG patterns qualitatively similar to the experimentally recorded EMG patterns. The model's predictive power compares it favourably to the existing models of the EMG patterns. 相似文献
995.
Sexual selection and population divergence I: The influence of socially flexible cuticular hydrocarbon expression in male field crickets (Teleogryllus oceanicus)
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Sonia Pascoal Magdalena Mendrok Christopher Mitchell Alastair J. Wilson John Hunt Nathan W. Bailey 《Evolution; international journal of organic evolution》2016,70(1):82-97
Debates about how coevolution of sexual traits and preferences might promote evolutionary diversification have permeated speciation research for over a century. Recent work demonstrates that the expression of such traits can be sensitive to variation in the social environment. Here, we examined social flexibility in a sexually selected male trait—cuticular hydrocarbon (CHC) profiles—in the field cricket Teleogryllus oceanicus and tested whether population genetic divergence predicts the extent or direction of social flexibility in allopatric populations. We manipulated male crickets’ social environments during rearing and then characterized CHC profiles. CHC signatures varied considerably across populations and also in response to the social environment, but our prediction that increased social flexibility would be selected in more recently founded populations exposed to fluctuating demographic environments was unsupported. Furthermore, models examining the influence of drift and selection failed to support a role of sexual selection in driving population divergence in CHC profiles. Variation in social environments might alter the dynamics of sexual selection, but our results align with theoretical predictions that the role social flexibility plays in modulating evolutionary divergence depends critically on whether responses to variation in the social environment are homogeneous across populations, or whether gene by social environment interactions occur. 相似文献
996.
Two types of use of “hammers” for cracking nuts by wild-living chimpanzees have been distinguished: (1) Relatively small stones
are used by the chimpanzee community at Bossou in Guinea to crack the nuts of oil palms growing on abandoned farmland, while
no nuts of wild tree species are cracked. (2) Larger hammer stones (and, at some sites, wooden clubs) are used in a more sophisticated
manner to crack the nuts of wild trees, but not of oil palms, in an area ranging from south-east Sierra Leone through Liberia
to the south-west of the Ivory Coast.
The first author (1986) has proposed that Type I has been copied by the chimpanzees, under pressure of food shortage, from
the local human population. New data now indicate that, at Bossou, while habitat deterioration has continued, the number of
hammer and anvil stones per utilized oil palm tree has approximately tripled in the last six years. The quantity of food obtained
from oil palm nut kernels, however, amounts to only a few percent of the total diet. For the rest these apes depend to a large
extent on many other agricultural products cultivated at Bossou which they are allowed freely to consume, including even cassava
(manioc) roots and sweet potatoes dug by them from the ground. Some factors determining the chosen size of hammers were analyzed.
Two abnormal hammers were found whose wear suggested a tentative, human-like manner of use.
No evidence has been found to indicate the use of stone tools by chimpanzees in the adjoining chimpanzee-inhabited areas around
the range of the Bossou community. Type II stone tool use was found, however, in a primary forest on a mountain≈13 km west
of Bossou. This is especially intriguing because the site is separated by a wide belt of drier rain forest from the belt of
very humid rain forest in the south where all the other known Type II sites are located. More research on the geographical
distribution of the use of stone tools by chimpanzees and on the underlying ecological factors is recommended. 相似文献
997.
E. D. Starin 《Primates; journal of primatology》1990,31(3):385-391
Temminck's red colobus (Procolobus badius temminckii) inhabiting the Abuko Nature Reserve, the Gambia, manipulate objects during solitary play, social play where there is an
obvious goal involved, agonistic and intimidation displays, and tug-of-war contests. Some of the object manipulation may be
regarded as true tool use and manufacture. Variation in the form and frequency of manipulative activities shows clear sex
differences which may relate to sex differences in social behavior. All observed cases of tool manufacture occurred at times
of maximum social upheaval for the individual concerned in the act. 相似文献
998.
999.
Conserved structural features are found upstream from the three co-ordinately regulated discoidin I genes of Dictyostelium discoideum 总被引:7,自引:0,他引:7
The discoidin I genes of Dictyostelium form a small, co-ordinately regulated multigene family. We have sequenced and compared the upstream regions of the DiscI-alpha, -beta and -gamma genes. For the most part the upstream regions of the three genes are non-homologous. The upstream sequences of the beta and gamma genes are exceedingly A + T-rich, while those of the alpha gene are less so. All three genes have a relatively G + C-rich region 20 to 40 base-pairs in length, found approximately 200 base-pairs 5' to the messenger RNA start site. This G + C-rich region 5' to the beta and gamma genes is flanked by short inverted repeats. Within this region, there is an 11 base-pair exact homology between the alpha and gamma genes, and a less perfect homology between these genes and the beta gene. The homology is flanked at a short distance by interspersed G and T residues. The gamma gene is greater than 90% A + T for greater than 800 base-pairs upstream. Further upstream there is a G + C-rich region that is also found inverted approximately 3.5 X 10(3) base-pairs away. The gamma and beta genes are tandemly linked, and the entire approximately 500 base-pair intergene region between the 3' end of the gamma gene and the 5' end of the beta gene is A + T-rich (approximately 90%) with the exception of the homology region 5' to the gamma gene. We demonstrate also the presence of a discoidin I pseudogene fragment having only 139 base-pairs of discoidin homology with greater than 8% mismatch. It is flanked upstream by five 39 base-pair G + C-rich repeats, and downstream by sequences that are extremely A + T-rich. We discuss the possible significance of the conserved G + C-rich structures on discoidin I gene expression. 相似文献
1000.
Robert St Charles Raymond E. Ciaglowski Daniel Walz Brian F.P. Edwards 《Journal of molecular biology》1984,176(3):421-423
Bovine platelet factor 4 has been crystallized by “vapor dilution” in space group P212121, , with four molecules, each 9505 Mr, in the asymmetric unit. The crystals diffract X-rays to better than 2.8 Å resolution. 相似文献