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排序方式: 共有409条查询结果,搜索用时 15 毫秒
1.
F. M. Swain J. Baysinger J. M. Bratt 《Origins of life and evolution of the biosphere》1976,7(3):239-257
Drill core samples of 42 Precambrian sedimentary, igneous, and metamorphic rocks were analyzed by heating under partial vacuum at 100°C and at 400°C to release hydrocarbons and other volatile products.The core samples yielded methane in amounts ranging from traces to 3 microliters per gram, but averaged much less. By way of comparison, samples of Middle Devonian Marcellus black shale, from Pennsylvania, yielded methane in amounts up to 7ul/g.Other straight chain hydrocarbons up to C11 were found in the volatile products, especially those obtained at 400°C, and benzene was a common product, also mainly in the 400°C experiments. Carbon dioxide and nitrogen appear to form a large part of the nonhydrocarbon volatiles in at least some of the samples.Spectral data indicate that the straight chain pyrolysis products of the Precambrian rocks are mainly alkenes, whereas those of the Devonian rocks, referred to above, are a mixture of alkanes and alkenes. Alkanes were however, obtained from several algae-bearing Middle Precambrian argillites. Available evidence indicates, although not conclusively, that the alkenes were contained in the rock rather than being produced from alkanes during pyrolysis.The writers believe that surface contamination in most of the drill cores was minimal owing to the low permeability of the rocks studied, and that contamination by drilling was also minimal.There is a reasonable possibility that the volatiles, if not formed from kerogen residues by the pyrolysis experiments, are in part juvenile igneous gases or are substances that were distilled out of the deeperlying rocks during intervals of folding and metamorphism, and subsequently accumulated at higher levels. 相似文献
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Per-Ola Arvidsson CharlotteEva Bratt Lars-Erik Andréasson Hans-Erik ?kerlund 《Plant Growth Regulation》1991,10(4):381-382
Book Review
Photosynthesis: Molecular biology and bioenergeticsG.S. Singhal, J. Barber, R.A. Dilley, Govindjee, R. Haselkorn and P. Mohanty (Eds), Proceedings of the International Workshop on Application of Molecular Biology and Bioenergetics of Photosynthesis. Berlin, Heidelberg, New York, London, Paris, Tokyo, Hong Kong and Narosa: Springer-Verlag, 1989. xiv+441 pages. DM 148,00. ISBN 3-540-50451-6 相似文献3.
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The carbon-13 nuclear magnetic resonance spectra of aquocobalamin, adenosylcobalamin, methylcobalamin, and (carboxymethyl)cobalamin have been interpreted. The assignments were made by a comparison of the spectra with that of cyanocobalamin, by a study of the pH dependence of the chemical shifts, by an analysis of the effect of the axial ligands on the carbon atoms of the corrin ring, and by a study of the specific line broadening effect of the paramagnetic ions Mn2+ and Gd3+. The chemical shift changes that accompany the "base-on"----"base-off" conversion of the organocobalamins demonstrate that the conformation of the "western" half of the corrin ring and the conformations of the a, b, c, d, f, and g side chains are relatively constant. In contrast, the conformations of the "eastern" half of the corrin ring and the e propionamide side chain are highly variable. 相似文献
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The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
相似文献
8.
Per-Ola Arvidsson Charlotte Eva Bratt Lars-Erik Andréasson Hans-Erik Åkerlund 《Photosynthesis research》1993,37(3):217-225
Photosystem II (PS II) particles isolated from spinach in the presence of 10 M CuSO4 contained 1.2 copper/300 Chl that was resistant to EDTA. When CuSO4 was not added during the isolation, PS II particles contained variable amounts of copper resistant to EDTA (0.1–1.1 copper/300 Chl). No correlation was found between copper content and oxygen evolving capacity of the PS II particles. To identify the copper binding protein, we developed a fractionation procedure which included solubilisation of PS II particles followed by precipitation with polyethylene glycol. A 22-fold purification of copper with respect to protein was achieved for a 28 kDa protein. Partial amino acid sequence of a 13 kDa fragment, obtained after V8 (endo Glu-C) protease treatment, showed identity with CP 26 over a 14 amino acid stretch. EPR measurements on the purified protein suggest oxygen and/or nitrogen as ligands for copper but tend to exclude sulfur. We conclude that the 28 kDa apoprotein of CP 26 from spinach binds one copper per molecule of CP 26. A possible function for this copper protein in the xanthophyll cycle is discussed.Abbreviations CP 26 and CP 29
chlorophyll a/b protein complex 26 and 29
- LHC II
light-harvesting chlorophyll a/b protein complex of Photosystem II
- SB14
sulfobetaine 14
A preliminary report of these results was presented at the IX Int. Congress on Photosynthesis, Nagoya, Japan, 1992. 相似文献
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