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1.
A technique for the simultaneous determination of [S]sulfide and [C]carbon dioxide produced in anaerobic aqueous samples dual-labeled with [S]sulfate and a C-organic substrate is described. The method involves the passive distillation of sulfide and carbon dioxide from an acidified water sample and their subsequent separation by selective chemical absorption. The recovery of sulfide was 93% for amounts ranging from 0.35 to 50 mumol; recovery of carbon dioxide was 99% in amounts up to 20 mumol. Within these delineated ranges of total sulfide and carbon dioxide, 1 nmol of [S]sulfide and 7.5 nmol of [C]carbon dioxide were separated and quantified. Correction factors were formulated for low levels of radioisotopic cross-contamination by sulfide, carbon dioxide, and volatile organic acids. The overall standard error of the method was +/-4% for sulfide and +/-6% for carbon dioxide. 相似文献
2.
Parker ET Cleaves HJ Callahan MP Dworkin JP Glavin DP Lazcano A Bada JL 《Origins of life and evolution of the biosphere》2011,41(6):569-574
Stanley Miller’s 1958 H2S-containing experiment, which included a simulated prebiotic atmosphere of methane (CH4), ammonia (NH3), carbon dioxide (CO2), and hydrogen sulfide (H2S) produced several alkyl amino acids, including the α-, β-, and γ-isomers of aminobutyric acid (ABA) in greater relative
yields than had previously been reported from his spark discharge experiments. In the presence of H2S, aspartic and glutamic acids could yield alkyl amino acids via the formation of thioimide intermediates. Radical chemistry
initiated by passing H2S through a spark discharge could have also enhanced alkyl amino acid synthesis by generating alkyl radicals that can help
form the aldehyde and ketone precursors to these amino acids. We propose mechanisms that may have influenced the synthesis
of certain amino acids in localized environments rich in H2S and lightning discharges, similar to conditions near volcanic systems on the early Earth, thus contributing to the prebiotic
chemical inventory of the primordial Earth. 相似文献
3.
Swire J 《Journal of molecular evolution》2007,64(5):558-571
Most investigations of the forces shaping protein evolution have focussed on protein function. However, cells are typically
50%–75% protein by dry weight, with protein expression levels distributed over five orders of magnitude. Cells may, therefore,
be under considerable selection pressure to incorporate amino acids that are cheap to synthesize into proteins that are highly
expressed. Such selection pressure has been demonstrated to alter amino acid usage in a few organisms, but whether “cost selection”
is a general phenomenon remains unknown. One reason for this is that reliable protein expression level data is not available
for most organisms. Accordingly, I have developed a new method for detecting cost selection. This method depends solely on
interprotein gradients in amino acid usage. Applying it to an analysis of 43 whole genomes from all three domains of life,
I show that selection on the synthesis cost of amino acids is a pervasive force in shaping the composition of proteins. Moreover,
some amino acids have different price tags for different organisms—the cost of amino acids is changed for organisms living
in hydrothermal vents compared with those living at the sea surface or for organisms that have difficulty acquiring elements
such as nitrogen compared with those that do not—so I also investigated whether differences between organisms in amino acid
usage might reflect differences in synthesis or acquisition costs. The results suggest that organisms evolve to alter amino
acid usage in response to environmental conditions.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
[Reviewing Editor: Hector Musto] 相似文献
4.
铁作为浮游植物所必需的微量元素,限制了全球超过三分之一海域的初级生产力,尤其是在高营养盐、低叶绿素海域(high nutrient low chlorophyll,HNLC)。长期以来海洋铁施肥被认为是一项可以降低大气二氧化碳含量的地球工程策略。然而通过13次海洋人工铁施肥(artificial ocean iron fertilization,aOIF)实验发现,铁的额外添加对海洋深层碳输出量的促进作用要显著低于预期。本文简要地总结了碳在海洋和大气中的循环过程,回顾了人工铁施肥实验对生物碳泵和碳通量等的影响,分析了从海洋铁施肥到海洋碳汇关键生物地球化学过程的影响因素。综上分析发现,科学界对生物碳泵过程及其调控机制的认识仍十分浅薄,考虑到海洋铁施肥还会对海洋生态系统带来一定的负面作用,铁施肥能否作为降低大气中CO2的有效手段,以达到碳中和并缓解温室效应仍需进一步研究。 相似文献
5.
Energised by the protonmotive force and with the intervention of inorganic catalysts, at base Life reacts hydrogen from a
variety of sources with atmospheric carbon dioxide. It seems inescapable that life emerged to fulfil the same role (i.e.,
to hydrogenate CO2) on the early Earth, thus outcompeting the slow geochemical reduction to methane. Life would have done so where hydrothermal
hydrogen interfaced a carbonic ocean through inorganic precipitate membranes. Thus we argue that the first carbon-fixing reaction
was the molybdenum-dependent, proton-translocating formate hydrogenlyase system described by Andrews et al. (Microbiology
143:3633–3647, 1997), but driven in reverse. Alkaline on the inside and acidic and carbonic on the outside - a submarine chambered hydrothermal
mound built above an alkaline hydrothermal spring of long duration - offered just the conditions for such a reverse reaction
imposed by the ambient protonmotive force. Assisted by the same inorganic catalysts and potential energy stores that were
to evolve into the active centres of enzymes supplied variously from ocean or hydrothermal system, the formate reaction enabled
the rest of the acetyl coenzyme-A pathway to be followed exergonically, first to acetate, then separately to methane. Thus
the two prokaryotic domains both emerged within the hydrothermal mound—the acetogens were the forerunners of the Bacteria
and the methanogens were the forerunners of the Archaea. 相似文献
6.
Technique for Simultaneous Determination of [35S]Sulfide and [14C]Carbon Dioxide in Anaerobic Aqueous Samples
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A technique for the simultaneous determination of [35S]sulfide and [14C]carbon dioxide produced in anaerobic aqueous samples dual-labeled with [35S]sulfate and a 14C-organic substrate is described. The method involves the passive distillation of sulfide and carbon dioxide from an acidified water sample and their subsequent separation by selective chemical absorption. The recovery of sulfide was 93% for amounts ranging from 0.35 to 50 μmol; recovery of carbon dioxide was 99% in amounts up to 20 μmol. Within these delineated ranges of total sulfide and carbon dioxide, 1 nmol of [35S]sulfide and 7.5 nmol of [14C]carbon dioxide were separated and quantified. Correction factors were formulated for low levels of radioisotopic cross-contamination by sulfide, carbon dioxide, and volatile organic acids. The overall standard error of the method was ±4% for sulfide and ±6% for carbon dioxide. 相似文献
7.
Methane, Carbon Dioxide, and Hydrogen Sulfide Production from the Terminal Methiol Group of Methionine by Anaerobic Lake Sediments 总被引:13,自引:9,他引:4
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A significant portion of the sulfide in lake sediments may be derived from sulfur-containing amino acids. Methionine degradation in Lake Mendota (Wisconsin) sediments was studied with gas chromatographic and radiotracer techniques. Temperature optimum and inhibitor studies showed that this process was biological. Methane thiol and dimethyl sulfide were produced in sediments when 1-μmol/ml unlabeled methionine was added. When chloroform (an inhibitor of one-carbon metabolism) was added to the sediments, methane thiol, carbon disulfide, and n-propane thiol were produced, even when no methionine was added. When 35S-labeled methionine was added to the sediments in tracer quantities (1.75 nmol/ml), labeled hydrogen sulfide was produced, and a roughly equal amount of label was incorporated into insoluble material. Methane and carbon dioxide were produced from [methyl-14C]methionine. Evidence is given favoring methane thiol as an intermediate in the formation of methane, carbon dioxide, and hydrogen sulfide from the terminal methiol group of methionine. Methionine may be an important source of sulfide in lake sediments. 相似文献
8.
Cell-free supernatant from Shewanella oneidensis MR-1 reduced carbon tetrachloride to chloroform, a suspension of Fe(III) and solid Fe(III) to iron (II). The putative reducing
agent was tentatively identified as menaquinone-1 (MQ-1)—a water-soluble menaquinone with a single isoprenoid residue in the
side chain. Synthetic MQ-1 reduced carbon tetrachloride to chloroform and amorphous iron (III) hydroxide to iron (II). To
test the generality of this result among menaquinones, the reductive activities of vitamin K2 (MQ-7)—a lipid-associated menaquinone with 7 or 8 isoprenoid residues—was evaluated. This molecule also reduced carbon tetrachloride
to chloroform and iron (III) to iron (II). The results indicate that molecules within the menaquinone family may contribute
to both the extracellular and cell-associated reduction of carbon tetrachloride and iron (III). 相似文献
9.
We recently showed in an animal model that iron isotopic composition varies substantially between different organs. For instance,
iron in ferritin-rich organs—such as the major storage tissues liver, spleen, and bone marrow—contain a larger fraction of
the heavy iron isotopes compared with other tissues, including blood. As a consequence, partitioning of body iron into red
blood cells and storage compartments should be reflected in the isotopic pattern of blood iron. To confirm this hypothesis,
we monitored blood iron isotope patterns in iron-overloaded subjects undergoing phlebotomy treatment by multicollector inductively
coupled plasma mass spectrometry. We found that bloodletting and consequential replacement of lost blood iron by storage iron
led to a substantial increase of the heavy isotope fraction in the blood. The progress of iron depletion therapy and blood
loss was quantitatively traceable by isotopic shifts of as much as +1‰ in δ(56Fe). These results show that—together with iron absorption efficiency—partitioning of iron between blood and iron storage
tissues is an important determinant of blood iron isotopic patterns, which could make blood iron isotopic composition the
first composite measure of iron metabolism in humans. 相似文献
10.
Kil-Yoon Kang Dong-Hyun Ahn Sun-Mi Jung Dong-Hun Kim Byung-Soo Chun 《Biotechnology and Bioprocess Engineering》2005,10(4):315-321
Supercritical carbon dioxide extraction was investigated as a method for removing lipids and bad flavor from tuna viscera.
To find the optimum conditions, different experimental variables, such as pressure, temperature, flow rate of solvent and
sample size, were evaluated for the effective removal of lipids and the undesirable smell. Ethanol was used as the entrainer,
with a 3% by vol CO2 flow rate. By increasing the pressure at constant temperature, the efficiency of the lipid removal was improved and the protein
was concentrated without denaturalization. The main fatty acids extracted from the tuna viscera were palmitic acid (16∶0),
heptadecanoic acid (17∶1), oleic acid (18∶1) and docosahexaenoic acid (22∶6). The major amino acids in the tuna viscera treated
by supercritical carbon dioxide were glutamic acid, leucine and lysine, and the free amino acids werel-proline, taurine andl-α-aminoadipic acid. 相似文献
11.
External pH affects the acidification induced by ethanol. The apparent specific rate of acidification depends on the dissociation
properties and production of carbon dioxide, acetic and lactic acid which are intermediates of ethanol oxidation. The organic
acids are transported by Nernst — Einstein diffusion. We designed and identified a new and simple mathematical model that
allows us to describe the effect of external pH on nonstationary transport of dissociated intermediates of ethanol oxidation. 相似文献
12.
Primitive terrestrial life – defined as a chemical system able to transfer its molecular information via self-replication
and to evolve – probably originated from the evolution of reduced organic molecules in liquid water. Several sources have
been proposed for the prebiotic organic molecules: terrestrial primitive atmosphere (methane or carbon dioxide), deep-sea
hydrothermal systems, and extraterrestrial meteoritic and cometary dust grains. The study of carbonaceous chondrites, which
contain up to 5% by weight of organic matter, has allowed close examination of the delivery of extraterrestrial organic material.
Eight proteinaceous amino acids have been identified in the Murchison meteorite among more than 70 amino acids. Engel reported
that l-alanine was surprisingly more abundant than d-alanine in the Murchison meteorite. Cronin also found excesses of l-enantiomers for nonprotein amino acids. A large collection of micrometeorites has been recently extracted from Antarctic
old blue ice. In the 50- to 100-μm size range, carbonaceous micrometeorites represent 80% of the samples and contain 2% of
carbon, on average. They might have brought more carbon than that involved in the present surficial biomass. The early histories
of Mars and Earth clearly show similarities. Liquid water was once stable on the surface of Mars, attesting the presence of
an atmosphere capable of deccelerating C-rich micrometeorites. Therefore, primitive life may have developed on Mars as well
and fossilized microorganisms may still be present in the near subsurface. The Viking missions to Mars in 1976 did not find
evidence of either contemporary or past life, but the mass spectrometer on the lander aeroshell determined the atmospheric
composition, which has allowed a family of meteorites to be identified as Martian. Although these samples are essentially
volcanic in origin, it has been recognized that some of them contain carbonate inclusions and even veins that have a carbon
isotopic composition indicative of an origin from Martian atmospheric carbon dioxide. The oxygen isotopic composition of these
carbonate deposits allows calculation of the temperature regime existing during formation from a fluid that dissolved the
carbon dioxide. As the composition of the fluid is unknown, only a temperature range can be estimated, but this falls between
0° and 90°C, which would seem entirely appropriate for life processes. It was such carbonate veins that were found to host
putative microfossils. Irrespective of the existence of features that could be considered to be fossils, carbonate-rich portions
of Martian meteorites tend to have material, at more than 1000 ppm, that combusts at a low temperature; i.e., it is an organic
form of carbon. Unfortunately, this organic matter does not have a diagnostic isotopic signature so it cannot be unambiguously
said to be indigenous to the samples. However, many circumstantial arguments can be made to the effect that it is cogenetic
with the carbonate and hence Martian. If it could be proved that the organic matter was preterrestrial, then the isotopic
fractionation between it and the carbon is in the right sense for a biological origin.
Received: January 22, 1998 / Accepted: February 16, 1998 相似文献
13.
Mass extinctions and ocean acidification: biological constraints on geological dilemmas 总被引:1,自引:1,他引:0
J. E. N. Veron 《Coral reefs (Online)》2008,27(3):459-472
The five mass extinction events that the earth has so far experienced have impacted coral reefs as much or more than any other
major ecosystem. Each has left the Earth without living reefs for at least four million years, intervals so great that they
are commonly referred to as ‘reef gaps’ (geological intervals where there are no remnants of what might have been living reefs).
The causes attributed to each mass extinction are reviewed and summarised. When these causes and the reef gaps that follow
them are examined in the light of the biology of extant corals and their Pleistocene history, most can be discarded. Causes
are divided into (1) those which are independent of the carbon cycle: direct physical destruction from bolides, ‘nuclear winters’
induced by dust clouds, sea-level changes, loss of area during sea-level regressions, loss of biodiversity, low and high temperatures,
salinity, diseases and toxins and extraterrestrial events and (2) those linked to the carbon cycle: acid rain, hydrogen sulphide,
oxygen and anoxia, methane, carbon dioxide, changes in ocean chemistry and pH. By process of elimination, primary causes of
mass extinctions are linked in various ways to the carbon cycle in general and ocean chemistry in particular with clear association
with atmospheric carbon dioxide levels. The prospect of ocean acidification is potentially the most serious of all predicted
outcomes of anthropogenic carbon dioxide increase. This study concludes that acidification has the potential to trigger a
sixth mass extinction event and to do so independently of anthropogenic extinctions that are currently taking place. 相似文献
14.
15.
A. J. MacDermott T. Fu R. Nakatsuka A. P. Coleman G. O. Hyde 《Origins of life and evolution of the biosphere》2009,39(5):459-478
In 1996, four α-methyl amino acids in the Murchison meteorite—L-isovaline, L-α-methylnorvaline, L-α-methyl-allo-isoleucine and L-α-methyl-isoleucine—were found to show significant enantiomeric excesses of the L form, ranging from 2% to 9%. Their deuterium
to hydrogen isotope ratios suggest they formed in the pre-solar interstellar gas cloud rather than during a later aqueous
processing phase on the asteroid parent body. In this paper we apply the techniques of the preceding two papers to compute
the parity-violating energy shifts of these amino acids. We find that, in the gas phase, the PVESs of the neutral L forms
of all four Murchison α-methyl amino acids are decisively negative, and there is even some correlation between the magnitudes of the L-excesses and
the magnitudes of the PVESs—all of which is at least consistent with an electroweak origin of the Murchison enantiomeric excesses. 相似文献
16.
Cultures of the marine diatom Phaeodactylum tricornutum Bohlin incorporated, a large proportion of the total fixed carbon (50% or more) into amino acids and amides during short periods of photo-assimilation of 14C-labelled carbon dioxide. Although increasing nitrogen limitation in a nitrate-limited chemostat had little significant effect on the proportion of C incorporated into amino acids and amides combined, it did affect the distribution of radioactivity within individual compounds of this group. In particular, increasing degrees of N deficiency reduced the proportion incorporated into amides to almost undetectable levels, reduced the proportion in alanine and increased the proportion in glutamic acid. Also, increasing N limitation decreased the relative synthesis of sugar phosphates and increased the proportion of C assimilated into intermediates of the tricarboxylic acid cycle. Reduced light intensity did not have any significant effect on the proportion of C incorporated into the total amino acids and amides, but did cause a decrease in the radioactivity 相似文献
17.
Sonia Gómez-Galera Eduard Rojas Duraialagaraja Sudhakar Changfu Zhu Ana M. Pelacho Teresa Capell Paul Christou 《Transgenic research》2010,19(2):165-180
Staple food crops, in particular cereal grains, are poor sources of key mineral nutrients. As a result, the world’s poorest
people, generally those subsisting on a monotonous cereal diet, are also those most vulnerable to mineral deficiency diseases.
Various strategies have been proposed to deal with micronutrient deficiencies including the provision of mineral supplements,
the fortification of processed food, the biofortification of crop plants at source with mineral-rich fertilizers and the implementation
of breeding programs and genetic engineering approaches to generate mineral-rich varieties of staple crops. This review provides
a critical comparison of the strategies that have been developed to address deficiencies in five key mineral nutrients—iodine,
iron, zinc, calcium and selenium—and discusses the most recent advances in genetic engineering to increase mineral levels
and bioavailability in our most important staple food crops. 相似文献
18.
Summary 1. Oat plants (variety ‘Yielder’) were grown in nutrient solution with nine different combinations of phosphorus and iron
supply.
2. Appearance of deficiency signs and responses in growth as reflected by fresh and dry weights are recorded.
3. The plants were analysed for mineral content, total nitrogen, protein, amino acids and organic acids.
4. The experiment was duplicated. External phosphorus affected the phosphorus content of the plants but external iron did
not affect the iron content. The quantity of minerals and organic compounds in the oats are considered in relation to both
medium-concentration and plant-content of phosphorus and iron and the ratio of phosphorus to iron.
5. The interrelationships between ratios of minerals and organic compounds in these oats are compared with those found for
other plants. 相似文献
19.
A novel iron-oxidizing, moderately thermophilic, acidophilic bacterium (strain “GSM”) was isolated from mineral spoil taken
from a gold mine in Montana. Biomolecular analysis showed that it was most closely related to Alicyclobacillus tolerans, although the two bacteria differed in some key respects, including the absence (in strain GSM) of ϖ-alicyclic fatty acids
and in their chromosomal base compositions. Isolate GSM was able to grow in oxygen-free media using ferric iron as terminal
electron acceptor confirming that it was a facultative anaerobe, a trait not previously described in Alicyclobacillus spp.. The acidophile used both organic and inorganic sources of energy and carbon, although growth and iron oxidation by
isolate GSM was uncoupled in media that contained both fructose and ferrous iron. Fructose utilization suppressed iron oxidation,
and oxidation of ferrous iron occurred only when fructose was depleted. In contrast, fructose catabolism was suppressed when
bacteria were harvested while actively oxidizing iron, suggesting that both ferrous iron- and fructose-oxidation are inducible
in this acidophile. Isolate GSM accelerated the oxidative dissolution of pyrite in liquid media either free of, or amended
with, organic carbon, although redox potentials were significantly different in these media. The potential of this isolate
for commercial mineral processing is discussed. 相似文献
20.
A selenium-containing peroxidase from the germinating barley grown on a selenium-containing artificial medium was isolated
and purified by means of cold acetone precipitation, Sephadex-G150 filtration, followed by DEAE-Sepharose chromatography and
sodium dodecyl sulfate — polyacrylamid gel electrophoresis. The form of selenium existing in the peptide assayed with paper
chromatography was selenomethionine. The amino acid composition of this enzyme was similar to those peroxidases from other
sources except amino acids Glu, Val Phe, Lys, and Arg. Electron-spin resonance (ESR) spectra recorded at −136°C showed that
both the selenium-containing peroxidase from germinating barley and horseradish peroxidase had same the ESR signals as iron
protoporphyine. Those results suggested that the germinating barley selenium-containing peroxidase is one of the peroxidase
isoenzymes. 相似文献