Astrobiological significance of minerals on Mars surface environment

Despite the large amount of geomorphological, geodynamic and geophysical data obtained from Mars missions, much is still unknown about Martian mineralogy and paragenetic assemblages, which is fundamental to an understanding of its entire geological history. Minerals are not only indicators of the physical–chemical settings of the different environments and their later changes, but also they could (and do) play a crucial astrobiological role related with the possibility of existence of extinct or extant Martian life. This paper aims: (1) to present a synoptic review of the main water-related Martian minerals (mainly jarosite and other sulfates) discovered up to the present time; (2) to emphasize their significance as environmental geomarkers, on the basis of their geological settings and mineral parageneses on earth (in particular in the context of some selected terrestrial analogues), and (3) to show that their differential UV shielding properties, against the hostile environmental conditions of the Martian surface, are of a great importance for the search for extraterrestrial life.     

Stable markers of oxidant damage to proteins and their application in the study of human disease

The mechanisms of formation and the nature of the altered amino acid side chains formed on proteins subjected to oxidant attack are reviewed. The use of stable products of protein side chain oxidation as potential markers for assessing oxidative damage in vivo in humans is discussed. The methods developed in the authors laboratories are outlined, and the advantages and disadvantages of these techniques compared with other methodologies for assessing oxidative damage to proteins and other macromolecules. Evidence is presented to show that protein oxidation products are sensitive markers of oxidative damage, that the pattern of products detected may yield information as to the nature of the original oxidative insult, and that the levels of oxidized side-chains can, in certain circumstances, be much higher than those of other markers of oxidation such as lipid hydroperoxides.     

云南民间药用琵琶甲无机元素及氨基酸分析

对云南民间药用瑟琶甲虫含有的无机元素及氨基酸进行了分析测定,结果表明:该甲虫含有9种人体必须微量元素,总含量为641.00μg/g;含有16种游离氨基酸和16种蛋白氨基酸,氨基酸种类齐全,含量高。研究为开发药用昆虫资源提供基本资料,为进一步探讨其药理作用提供参考     

Solar radiation incident on the Martian surface

Summary Calculations indicate that the maximum daily solar radiation reaching the Martian surface is about 325 cal/cm² during southern hemisphere summer at latitude of about 40°S. In the ultraviolet region of the spectrum, the radiation reaching the surface at wavelengths greater than 2800 Å is within 10% of the radiation incident on the atmosphere. There is significant extinction of radiation in the spectral region near 2500 Å in mid and high latitudes due to absorption of radiation by ozone; radiation reaching the surface may be reduced to one one-thousandth of that incident on the atmosphere during winter. Virtually no radiation of wavelengths less than 1900 Å reaches the surface because of absorption by the large column abundance of carbon dioxide. Daily and latitudinal distributions of radiation are presented for wavelengths of 3000, 2500 and 2000 Å.     

Search for bioorganic compounds and organisms on Mars

A prototype of new instrument is under construction as a part of Russian Mars program to search for bioorganic compounds and microorganisms which might be frozen in rock under the places where the traces of water were found or near the poles of Mars. The proposed instrument consists of a quadrupole mass spectrometer (QMS) to detect chemical compounds and a fluorescent microscope system (FMS) to detect organisms and bioorganic compounds in bulk.     

Possible sources of new information in the magnetocardiogram

The theoretical basis for the relationship between the electric and magnetic fields of the heart is examined in terms of impressed currents, J^j, from a biologically active region imbedded in an Ohmic conductor. For quasistatic sources in a uniform conductor, it is shown that the problem of measuring the electrocardiogram or magnetocardiogram is an inverse problem rendered non-unique by the presence of so-called silent sources. An important class of sources, toroidal J^j, are silent electrically and not silent magnetically and these sources result in inherent differences between the information content of the electric and magnetic measurement techniques. A hypothetical example of cardiac activation departing from the conventional uniform double-layer model is presented to indicate that electrically silent sources cannot be ruled out a priori without careful magnetic measurements.     

Life on Mars: chemical arguments and clues from Martian meteorites

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     

Focal oxidant and Ras signaling on the ER surface activates autophagy

Eukaryotic cells react to a variety of intrinsic and extrinsic stresses with patterned responses, each triggered within relevant subcellular domains. One feature common to a variety of cellular stresses is the production of reactive oxidant species (ROS), suggesting an additional element of oxidative stress. We addressed the role of oxidants in ER stress and find instead that localized production of ROS by the ER mediates protective signaling, leading among other things to Ras-dependent activation of autophagy. Thus, focal oxidant production is incorporated into stress response pathways, in this case participating in homeostatic signaling circuits on the ER surface.     

Possible sources of dye-related signal correlation bias in two-color DNA microarray assays

DNA microarray analyses commonly use two spectrally distinct fluorescent labels to simultaneously compare different mRNA pools. Signal correlation bias currently limits accepted resolution to twofold changes in gene expression. This bias was investigated by (i) examining fluorescence and absorption spectra and changes in relative fluorescence of DNAs labeled with the Cy3, Cy5, Alexa Fluor 555, and Alexa Fluor 647 dyes and by (ii) using homotypic hybridization assays to compare the Cy dye pair with the Alexa Fluor dye pair. Cy3 or Cy5 dye-labeled DNA exhibited reduced fluorescence and absorption anomalies that were eliminated by nuclease treatment, consistent with fluorescence quenching that arises from dye-dye or dye-DNA-dye interactions. Alexa Fluor 555 and Alexa Fluor 647 dye-labeled DNA exhibited little or no such anomalies. In microarray hybridization, the Alexa Fluor dye pair provided higher signal correlation coefficients (R2) than did the Cy dye pair; at the 95% prediction level, a 1.3-fold change in gene expression was significant using the Alexa Fluor dye pair. Lowered signal correlation of the Cy dye pair was associated with high variance in Cy5 dye signals. These results indicate that fluorescence quenching may be a source of signal bias associated with the Cy dye pair.     

Smectite clays in Mars soil: Evidence for their presence and role in Viking biology experimental results

Summary Various chemical, physical and geological observations indicate that smectite clays are probably the major components of the Martian soil. Satisfactory ground-based chemical simulation of the Viking biology experimental results was obtained with the smectite clays nontronite and montmorillonite when they contained iron and hydrogen as adsorbed ions. Radioactive gas was released from the medium solution used in the Viking Labeled Release (LR) experiment when interacted with the clays, at rates and quantities similar to those measured by Viking on Mars. Heating of the active clay (mixed with soluble salts) to 160°C in CO₂ atmosphere reduced the decomposition activity considerably, again, as was observed on Mars. The decomposition reaction in LR experiment is postulated to be iron-catalyzed formate decomposition on the clay surface. The main features of the Viking Pyrolytic Release (PR) experiment were also simulated recently (Hubbard, 1979) which the iron clays, including a relatively low 1st peak and significant 2nd peak.The accumulated observations on various Martian soil properties and the results of simulation experiments, thus indicate that smectite clays are major and active components of the Martian soil. It now appears that many of the results of the Viking biology experiments can be explained on the basis of their surface activity in catalysis and adsorption.     

Investigation of the relationships between plasma levels of ascorbate, vitamin E and β-carotene and the frequency of sister-chromatid exchanges and release of reactive oxidants by blood leucocytes from cigarette smoker

In this study the frequencies of sister-chromatid exchanges (SCEs) were controled with measurements of the release of reactive oxidants by phagocytes, as determined by luminol-enhanced chemiluminescence (LECL), and levels of the anti-oxidants ascorbate, β-carotene and vitamine E in blood speciments taken from 65 young asymptomatic cigarette smokers. Increased SCE frequencies related with LECL responses (p < 0.0075) of activated blood phagocytes. Anti-oxidant levels did not correlate with either LECL or SCEs. These findings indicated that increased generation of reactive oxidants by circulating phagocytes from cigarette smokers are associated cytogenetic changes.     

浑河流域水体污染的季节性变化及来源

2009年枯水期(4月)、丰水期(8月)和平水期(11月)对浑河流域水体进行采样,分析了一个水文年内水体污染变化特征及水体污染的来源.结果表明:浑河流域水体下游(七间房-于家房)NH4+-N污染较重,水质属于Ⅴ类甚至劣Ⅴ类(＞1.5 mg·L-1),大部分监测断面枯水期NH4+-N浓度较高;水体中总磷含量较低(均值为0...     

Description of light ion production cross sections and fluxes on the Mars surface using the QMSFRG model

The atmosphere of Mars significantly attenuates the heavy ion component of the primary galactic cosmic rays (GCR), however, increases the fluence of secondary light ions (neutrons, and hydrogen and helium isotopes) because of particle production processes. We describe results of the quantum multiple scattering fragmentation (QMSFRG) model for the production of light nuclei through the distinct mechanisms of nuclear abrasion and ablation, coalescence, and cluster knockout. The QMSFRG model is shown to be in excellent agreement with available experimental data for nuclear fragmentation cross sections. We use the QMSFRG model and the space radiation transport code, HZETRN to make predictions of the light particle environment on the Martian surface at solar minimum and near maximum. The radiation assessment detector (RAD) experiment will be launched in 2009 as part of the Mars Science Laboratory (MSL). We make predictions of the expected results for time dependent count-rates to be observed by the RAD experiment. Finally, we consider sensitivity assessments of the impact of the Martian atmospheric composition on particle fluxes at the surface.     

Possible involvement of a cell surface glycoprotein in the differentiation of skeletal myoblasts

From a highly myogenic permanent line of rat skel-myoblasts (L6), we have isolated two classes of single step concanavalin A-resistant mutants. The RI class is about 2-fold and RII about 5-fold more resistant than the parental cells to the lethal action of concanavalin A. In all of the mutants, both the morphological differentiation (i.e. fusion to form myotubes) and biochemical differentiation, measured by the appearance of creatine kinase and acetylcholine receptors, are absent. The biochemical lesion in the RI type of mutants is not known, but RII type of mutants is unable to catalyze transfer of mannose from GDP-mannose into a lipid-linked form. Concanavalin A binding to separated membrane proteins from RII type of mutants on polyacrylamide gels is reduced 80% compared to wild type cells. In the RI type of mutants, however, only one major band, approximately 46,000 daltons, does not bind concanavalin A to the same extent as the wild type cells. In somatic cell hybridizations, RI type of mutants complements the RII type. In the hybrids, fusion as well as creatine kinase and acetylcholine receptors reappear, although not to the same extent as in the wild type cells. The 46,000-dalton band also reappears in the complementing hybrids. Thus, this protein may play some crucial role in myogenesis.     

Calcium signaling and oxidant stress in the vasculature

Recent evidence suggests that oxidant stress plays a major role in several aspects of vascular biology. Oxygen free radicals are implicated as important factors in signaling mechanisms leading to vascular pathologies such as postischemic reperfusion injury and atherosclerosis. The role of intracellular Ca(2+) in these signaling events is an emerging area of vascular research that is providing insights into the mechanisms mediating these complex physiological processes. This review explores sources of free radicals in the vasculature, as well as effects of free radicals on Ca(2+) signaling in vascular endothelial and smooth muscle cells. In the endothelium, superoxides enhance and peroxides attenuate agonist-stimulated Ca(2+) responses, suggesting differential signaling mechanisms depending on radical species. In smooth muscle cells, both superoxides and peroxides disrupt the sarcoplasmic reticulum Ca(2+)-ATPase, leading to both short- and long-term effects on smooth muscle Ca(2+) handling. Because vascular Ca(2+) signaling is altered by oxidant stress in ischemia-related disease states, understanding these pathways may lead to new strategies for preventing or treating arterial disease.