SEARCH · Search PubMed

Results for “Mars”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources

PubMed1997

Possible complex organic compounds on Mars.

It is suggested that primitive Mars had somehow similar environments as primitive Earth. If life was born on the primitive earth using organic compounds which were produced from the early Earth environment, the same types of organic compounds were also formed on primitive Mars. Such organic compounds might have been preserved on Mars still now. We are studying possible organic formation on primitive and present Mars. A gaseous mixture of CO2, CO, N2 and H2O with various mixing ratios were irradiated with high energy protons (major components of cosmic rays). Hydrogen cyanide and formaldehyde were detected among volatile products, and yellow-brown-colored water-soluble non-volatile substances were produced, which gave amino acids after acid-hydrolysis. Major part of "amino acid precursors" were not simple molecules like aminonitriles, but complex compounds which eluted earlier than free amino acids in cation-exchange HPLC. These organic compounds should be major targets in the future Mars mission. Strategy for the detection of the complex organics on Mars will be discussed.

Amino Acids↗

PubMed1995

Site selection for Mars exobiology.

The selection of sites on Mars that have a high priority for exobiological research is fundamental for planning future exploration. The most immediate need is to identify targets for high resolution orbital imaging during the Mars Observer and Mars '94/'96 missions that can be used to refine site priorities for surface exploration. We present an objective approach to site selection whereby individual sites are selected and scored, based on the presence of key geological features which indicate high priority environments. Prime sites are those that show evidence for the prolonged activity of liquid water and which have sedimentary deposits that are likely to have accumulated in environments favorable for life. High priority areas include fluvio-lacustrine (stream-fed lake systems), springs, and periglacial environments. Sites where mineralization may have occurred in the presence of organisms (e.g. springs) are given high priority in the search for a fossil record on Mars. A systematic review of Viking data for 83 sites in the Mars Landing Site Catalog resulted in the selection of 13 as being of exobiological interest. The descriptions of these sites were expanded to address exobiological concerns. An additional five sites were identified for inclusion in the second edition of the MLSC. We plan to broaden our site selection activities to include a systematic global reconnaissance of Mars using Viking data, and will continue to refine site priorities for exobiological research based on data from future missions in order to define strategies for surface exploration.

Exobiology↗

PubMed2000

The missing organic molecules on Mars.

GC-MS on the Viking 1976 Mars missions did not detect organic molecules on the Martian surface, even those expected from meteorite bombardment. This result suggested that the Martian regolith might hold a potent oxidant that converts all organic molecules to carbon dioxide rapidly relative to the rate at which they arrive. This conclusion is influencing the design of Mars missions. We reexamine this conclusion in light of what is known about the oxidation of organic compounds generally and the nature of organics likely to come to Mars via meteorite. We conclude that nonvolatile salts of benzenecarboxylic acids, and perhaps oxalic and acetic acid, should be metastable intermediates of meteoritic organics under oxidizing conditions. Salts of these organic acids would have been largely invisible to GC-MS. Experiments show that one of these, benzenehexacarboxylic acid (mellitic acid), is generated by oxidation of organic matter known to come to Mars, is rather stable to further oxidation, and would not have been easily detected by the Viking experiments. Approximately 2 kg of meteorite-derived mellitic acid may have been generated per m(2) of Martian surface over 3 billion years. How much remains depends on decomposition rates under Martian conditions. As available data do not require that the surface of Mars be very strongly oxidizing, some organic molecules might be found near the surface of Mars, perhaps in amounts sufficient to be a resource. Missions should seek these and recognize that these complicate the search for organics from entirely hypothetical Martian life.

Alkanes↗

PubMed2006

Survival of methanogens during desiccation: implications for life on Mars.

The relatively recent discoveries that liquid water likely existed on the surface of past Mars and that methane currently exists in the martian atmosphere have fueled the possibility of extant or extinct life on Mars. One possible explanation for the existence of the methane would be the presence of methanogens in the subsurface. Methanogens are microorganisms in the domain Archaea that can metabolize molecular hydrogen as an energy source and carbon dioxide as a carbon source and produce methane. One factor of importance is the arid nature of Mars, at least at the surface. If one is to assume that life exists below the surface, then based on the only example of life that we know, liquid water must be present. Realistically, however, that liquid water may be seasonal just as it is at some locations on our home planet. Here we report on research designed to determine how long certain species of methanogens can survive desiccation on a Mars soil simulant, JSC Mars-1. Methanogenic cells were grown on JSC Mars-1, transferred to a desiccator within a Coy anaerobic environmental chamber, and maintained there for varying time periods. Following removal from the desiccator and rehydration, gas chromatographic measurements of methane indicated survival for varying time periods. Methanosarcina barkeri survived desiccation for 10 days, while Methanobacterium formicicum and Methanothermobacter wolfeii were able to survive for 25 days.

Desiccation↗

PubMedDate not supplied

Space radiation dose estimates on the surface of Mars.

A future goal of the U.S. space program is a commitment to the manned exploration and habitation of Mars. An important consideration of such missions is the exposure of crew members to the damaging effects of ionizing radiation from high-energy galactic cosmic ray fluxes and solar proton flares. The crew will encounter the most harmful radiation environment in transit to Mars from which they must be adequately protected. However, once on the planet's surface, the Martian environment should provide a significant amount of protection from free-space radiative fluxes. In current Mars scenario descriptions, the crew flight time to Mars is estimated to be anywhere from 7 months to over a year each way, with stay times on the surface ranging from 20 days to 2 years. To maintain dose levels below established astronaut limits, dose estimates need to be determined for the entire mission length. With extended crew durations on the surface anticipated, the characterization of the Mars radiation environment is important in assessing all radiation protection requirements. This synopsis focuses on the probable doses incurred by surface inhabitants from the transport of galactic cosmic rays and solar protons through the Mars atmosphere.

Astronauts↗

PubMed1992

Interaction of MAR-sequences with nuclear matrix proteins.

The recent discovery of DNA sequences responsible for the specific attachment of chromosomal DNA to the nuclear skeleton (MARs/SARs) was an important step towards our understanding of the functional and structural organization of eukaryotic chromatin [Mirkovitch et al.: Cell 44:273-282, 1984; Cockerill and Garrard: Cell 44:273-282, 1986]. A most important question, however, remains the nature of the matrix proteins involved in the specific binding of the MARs. It has been shown that topoisomerase II and histone H1 were capable of a specific interaction with SARs by the formation of precipitable complexes [Adachi et al.: EMBO J8:3997-4006, 1989; Izaurralde et al.: J Mol Biol 210:573-585, 1989]. Here, applying a different approach, we were able to "visualize" some of the skeletal proteins recognizing and specifically binding MAR-sequences. It is shown that the major matrix proteins are practically the same in both salt- and LIS-extracted matrices. However, the relative MAR-binding activity of the individual protein components may be different, depending on the method of matrix preparation. The immunological approach applied here allowed us to identify some of the individual MAR-binding matrix proteins. Histone H1 and nuclear actin are shown to be not only important components of the matrix, but to be involved in a highly efficient interaction with MAR-sequences as well. Evidence is presented that proteins recognized by the anti-HMG antibodies also participate in MAR-interactions.

Animals↗

PubMed2005

Using Drosophila eye as a model system to characterize the function of mars gene in cell-cycle regulation.

Human hepatoma up-regulated protein (HURP), a cell-cycle regulator, is found consistently overexpressed in human hepatocellular carcinoma. At present, the function of HURP in cell-cycle regulation and carcinogenesis remains unclear. In database mining, we have identified a mars gene in Drosophila, which encodes a protein with a high similarity to HURP in its guanylate kinase-associated protein (GKAP) motif. Overexpression but not down-regulation of mars in eye discs resulted in a higher mitotic index along with a high frequency of mitotic defects, including misalignment of chromosomes and mispositioned centrosomes, at the second mitotic wave (SMW). The consequence of mitotic defects impairs cell-cycle progression, and causes cell death posterior to the furrow. Immunocytochemical studies also have indicated that the expression of Mars is cell cycle regulated, and that its subcellular localization is dynamically changed during cell-cycle progression. Furthermore, we also demonstrated that the first 198 amino acids at the N-terminus of Mars are responsible for the degradation of Mars in non-mitotic cells. Together, we report the use Drosophila eye as a model system to characterize the function of the mars gene in cell-cycle regulation.

Amino Acid Motifs↗

PubMed2003

Hepatic and systemic haemodynamic changes after MARS in patients with acute on chronic liver failure.

Hyperdynamic circulation and portal hypertension characterize acute on chronic liver failure (AoCLF), partially because of circulating mediators. Molecular Absorbents Recirculating System (MARS) may remove some of these substances. The objective of this study was to evaluate the effect of MARS on portal pressure, systemic haemodynamic and endogenous vasoactive systems. MARS treatment was performed in four patients with AoCLF (mean age 36.2 +/- 3.1 years; Child-Pugh C 11 +/- 1.8 points; three AAH and one NASH). Systemic and splanchnic haemodynamic measurements were performed before and after each session. Plasmatic renin activity (PRA) and NE were measured at baseline, at the end of the sessions and 10 days after MARS. All patients had severe portal hypertension (HVPG=23 +/- 7 mmHg) and pronounced hyperdynamic circulation (MAP 77.8 +/- 11.7 mmHg; CO 11.2 +/- 1.6 L/min; SVRI 478.5 +/- 105 dyne s/cm5). HVPG decreased at the end of the first session in all patients (23 +/- 7 mmHg vs 17.3 +/- 9.9 mmHg; P=0.05; mean decrease 32 +/- 24%) because of a decrease in WHVP (40.7 +/- 5.6 mmHg vs 34 +/- 9.6 mmHg; P=0.025; mean decrease 18 +/- 19%). MARS significantly attenuated hyperdynamic circulation as shown by a decrease in CO (11.2 +/- 1.6 L/min vs 9.4 +/- 2.1 L/min; mean decrease 12.3%), with an increase in MAP (77.8 +/- 11.7 mmHg vs 84.2 +/- 8 mmHg; mean increase 9.2%) and in SVRI (478.5 +/- 105 dyne s/cm5 vs 622 +/- 198 dyne s/cm5; mean increase 41%). PRA and NE decreased significantly (14.2 +/- 17.2 ng/mL/h vs 3.7 +/- 3.4 ng/mL/h; 1319 +/- 1002 pg/mL vs 617 +/- 260 pg/mL, respectively). The NE decrease was correlated to HVPG decrease (r=1, P=0.01). MARS decreases portal hypertension and ameliorates hyperdynamic circulation in patients with AoCLF, probably mediated by clearance of vasoactive substances. Further studies are necessary to confirm these results.

Adult↗

PubMed2003

MARS treatment in posthepatectomy liver failure.

Posthepatectomy liver failure (PHLF) is a dramatic complication following extensive liver resection or liver resection in a compromised liver, leading to death in 80% of cases. Molecular Adsorbent Recirculating System (MARS) is able to extract water and protein bound toxins out of the blood in liver failure patients. This paper describes the initial experience in the Netherlands using the MARS liver assist device in five patients with PHLF. In all patients, improvement of biochemical parameters was observed during MARS treatment along with clinical improvement in three patients. One patient survived. No clear guidelines for MARS treatment and prognostic factors for outcome after MARS treatment with regard to this patient group are available. In this paper, a MARS treatment regimen for PHLF is suggested based on literature and our own experience.

Aged↗

PubMed2003

Case report of the first Severe Acute Respiratory Syndrome patient in China: successful application of extracorporeal liver support MARS therapy in multiorgan failure possibly induced by Severe Acute Respiratory Syndrome.

A previously healthy patient was transferred to our infectious department with a 9-day-history of continued fever. The patient was placed on assisted respiration support in addition to anti-viral medication. The diagnosis of SARS (Severe Acute Respiratory Syndrome) was made in view of the severe hypoxemia and the characteristic symptoms exhibited by the patient. Despite the best intensive therapy, he clinically deteriorated into multiorgan dysfunction syndrome (MODS) including additional dysfunction of kidney, liver, and heart. We initiated MARS therapy (extracorporeal liver support utilizing albumin dialysis) with intention to positively influence the organ functions in his MODS on the basis of recently published studies which suggested a positive impact of MARS in multiorgan failure secondary to respiratory illnesses and the possible influence on inflammatory mediators and cytokines. The application of 4 intermittent MARS treatments (8 h each, mean blood flow rate 180 ml/min) on 4 consecutive days resulted in an immediate improvement of clinical conditions within the treatment days. The further improvement of organ functions allowed withdrawing the patient from ventilatory support 13 days after start of MARS, and 44 days after admission he was discharged home with completely resolved organ functions and laboratory abnormalities. SARS is a severe form of the epidemic outbreak of atypical pneumonia which remains poorly defined regarding etiology and special therapy recommendations. However, the development and aggravation of this ARDS-like severe acute respiratory syndrome is pathologically associated with the systemic inflammatory response syndrome (SIRS) which may then mediate or cause MODS. To our knowledge, this is the first report of an application of MARS therapy in MODS which was probably induced by SARS in a patient in China which improved the clinical condition of the patient in multi-organ failure secondary to respiratory failure indicating that MARS might be an additional therapeutic option in multiorgan failure induced by SARS.

China↗

PubMed2001

[MARS (Molecular Adsorbent Recycling System) as a novel hepatic detoxification procedure until orthotopic liver transplantation].

MARS (Molecular Adsorbent Recycling System) as a novel hepatic detoxification procedure until orthotopic liver transplantation. We report the case of a 30-year-old man who was admitted because of acute liver failure due to longstanding ethanol abuse. On conservative treatment liver function progressively deteriorated and the patient was listed for orthotopic liver transplantation. Because of a rapidly progressive and clinically severe hepatic encephalopathy together with increasing bilirubin levels (maximum 39 mg/dl) we began intermittent extracorporeal detoxification with the Molecular Adsorbent Recycling System (MARS). Under MARS therapy serum bilirubin decreased significantly (to 20 mg/dl after three cycles) and encephalopathy improved rapidly until the patient was completely oriented. No effect of MARS on liver function could be demonstrated. MARS treatment was successfully continued until a cadaver liver became available after 48 days and the patient was transplanted in good clinical and neurological condition and without complications. MARS represents a novel detoxification technique which, in patients with acute liver failure, can successfully replace hepatic detoxification until orthotopic liver transplantation can be performed.

Adult↗

PubMed1996

Construction of a chromosome specific library of human MARs and mapping of matrix attachment regions on human chromosome 19.

Using a novel procedure a representative human chromosome 19-specific library was constructed of short sequences, which bind preferentially to the nuclear matrix (matrix attachment regions, or MARs). Judging by 20 clones sequenced so far, the library contains > 50% of human inserts, about 90% of which are matrix-binding by the in vitro test. Computer analysis of sequences of eight human MARs did not reveal any significant homologies with the EMBL Nucleotide Data Base entries as well as between MARs themselves. Eight MARs were assigned to individual positions on the chromosome 19 physical map. The library constructed can serve as a good source of MAR sequences for comparative analysis and classification and for further chromosome mapping of MARs as well.

Base Sequence↗

PubMed1998

The influences of two plant nuclear matrix attachment regions (MARs) on gene expression in transgenic plants.

Nuclear matrix attachment regions (MARs) are thought to influence gene expression by anchoring active chromatin to the proteinaceous nuclear matrix. In this study, two plant DNA fragments with strong MAR activity were selected and tested for their effects on expression of a linked reporter gene in transgenic tobacco. One MAR was isolated from the 5' flanking region of a pea vicilin gene previously reported to be expressed in a copy number-dependent manner in transgenic tobacco. A second MAR was isolated from the genome of Arabidopsis thaliana by preselection for autonomously replicating sequence (ARS) activity in yeast. Flanking copies of the A. thaliana MAR stimulated median reporter gene expression in transgenic plants by five to ten fold. Neither MAR significantly reduced the variation in transgene expression between individual transformants, or conferred copy number-dependence in gene expression.

Arabidopsis↗

PubMed1993

Genetic and functional analysis of the multiple antibiotic resistance (mar) locus in Escherichia coli.

A 7.8-kbp fragment of chromosomal DNA from a region controlling multiple antibiotic resistance (Mar) in Escherichia coli has been sequenced. Within the fragment is a potential divergent promoter region including marO, which contains two pairs of direct repeats, suggesting possible operator-regulatory sites. To the left of marO (region I) are one or two transcriptional units with three putative open reading frames (ORFs) encoding 64, 157, and 70 amino acids. To the right (region II) is a transcriptional unit containing three putative ORFs (ORF125/144, ORF129, and ORF72). Of six independent Mar mutants, four had mutations within the ORF encoding the first putative protein (ORF125/144) downstream of marO, including three different single-point mutations and an IS2 insertion. One of the other mutations occurred in marO (20-bp duplication), and the other occurred in a site in marO or ORF144 (a 1-bp change). All six mutations led to increased transcription of the region II transcript. High-copy-number plasmids containing marO and the adjacent ORF125/144 region from a wild-type source but not from a Mar mutant reduced the antibiotic resistance of a Mar mutant to levels comparable to those of wild-type cells. High-copy-number plasmids containing wild-type marO alone caused an increase in resistance to tetracycline, chloramphenicol, and norfloxacin in a wild-type strain. The nature of the Mar mutations and the results of the complementation studies suggest that ORF125/144 encodes a repressor (designated MarR) which acts at marO. The second ORF (ORF129), designated marA, would encode a protein, MarA, whose sequence shows strong similarity to those of a family of positive transcriptional regulators. A Tn5 insertion in marA inactivated the multiresistance phenotype of Mar mutants. The function of ORF72, designated marB, encoding the third putative protein in the operon, and that of other ORFs detected within the 7.8-kb fragment have not yet been determined.

Amino Acid Sequence↗

PubMed1994

Dual regulation of inaA by the multiple antibiotic resistance (mar) and superoxide (soxRS) stress response systems of Escherichia coli.

The roles of the marRAB (multiple antibiotic resistance) operon and soxRS (superoxide response) genes in the regulation of inaA, an unlinked weak-acid-inducible gene, were studied. inaA expression was estimated from the beta-galactosidase activity of a chromosomal inaA1::lacZ transcriptional fusion. marR mutations that elevate marRAB transcription and engender multiple antibiotic resistance elevated inaA expression by 10- to 20-fold over that of the wild-type. Similarly, one class of inaA constitutive mutants that mapped to the mar region were multiply antibiotic resistant. Overexpression of marA alone on a multicopy plasmid caused high constitutive expression of inaA in a strain with an extensive (39-kbp) marRAB deletion. Salicylate, an inducer of marRAB and of an unidentified mar-independent antibiotic resistance system, induced inaA by 6-fold. A portion of this induction was also mar independent. Two soxRS constitutive mutants that were tested showed elevated levels of inaA. Paraquat, an inducer of the soxRS system, elevated inaA expression by 6- to 9-fold. This induction was soxRS dependent and not mar dependent, whereas induction of inaA by salicylate was not dependent on soxRS. Paraquat induced resistance to norfloxacin in the mar-deleted strain but not in a soxRS-deleted strain. Thus, induction of multiple antibiotic resistance and inaA by salicylate occurs via mar and an unidentified pathway, while induction by paraquat occurs via soxRS.

2,4-Dinitrophenol↗

PubMed2001

The bacterial multiple antibiotic resistant (Mar) phenotype leads to increased tolerance to tea tree oil.

Mutants of Escherichia coil strain AG100 exhibiting the multiple antibiotic resistance (Mar) phenotype demonstrated a greater level of tolerance to tea tree oil (TTO) compared with the parent strain. The ability of TTO to kill all E. coil strains studied was greater at 37 than at 30 degrees C. Growth of parent strain AG100 in the presence of salicylate, which induces the mar operon leading to the Mar phenotype, also increased tolerance to TTO. Escherichia coli Mar mutant YL1 demonstrated greater tolerance to antimicrobial terpenes found in TTO and did not leak K+ as rapidly in the presence of TTO when compared with its parent strain AG100. Attempts to isolate Mar mutants of Staphylococcus aureus using tetracycline gradients proved unsuccessful. However, when grown in the presence of salicylate, S. aureus strain BB255 demonstrated greater tolerance to TTO and did not leak K+ as rapidly in the presence of TTO compared with this strain grown without additions. This evidence demonstrates that bacterial Mar phenotypes increase tolerance to the killing action of TTO. This work also adds indirect evidence that the target of TTO is the cell membrane.

Anti-Infective Agents, Local↗

PubMedDate not supplied

The MAR test as immunologic screening of male infertility.

The mixed antiglobulin reaction was developed for detection of platelet antibody and then modified to demonstrate antibodies on spermatozoa. We have used the test as a simple method of screening for antibodies in the male, performing the test during the analysis of semen samples. We evaluated 320 samples from partners of sterile couples attending our Sterility centers. The IgG MAR test was not applicable to 82 samples because the sperm concentration and sperm motility was not sufficient. In all uncertain, positive and firmly positive cases of MAR test and in 50 negative cases of IgG MAR test, as control group we performed MAR test for IgA. We correlate our results with the sperm test penetration, SCMC test and identification of antisperm antibodies test and Isojima test for sperm immobilizing antibodies. Our results reconfirm the utility of IgG MAR test as screening test for the presence of antibodies but its positiveness requires the performance of IgA MAR test and, if necessary, of other tests in order to diagnose sterility depending on immunologic factors.

Antibodies↗

PubMed1994

Spectroscopy of Mars from 2.04 to 2.44 micrometers during the 1993 opposition: absolute calibration and atmospheric vs mineralogic origin of narrow absorption features.

We present moderate-resolution (lambda/delta lambda = 300 to 370) reflectance spectra of Mars from 2.04 to 2.44 micrometers that were obtained at UKIRT during the 1993 opposition. Seven narrow absorption features were detected and found to have a Mars origin. By comparison with solar and Mars atmospheric spectra, five of these features were attributed all or in part to Mars atmospheric CO2 or CO(2.052 +/- 0.003, 2.114 +/- 0.002, 2.150 +/- 0.003, 2.331 +/- 0.001, and 2.357 +/- 0.002 micrometers). Two of the bands (2.331 +/- 0.001 and 2.357 +/- 0.002 micrometers) appear to have widths and depths that are consistent with additional, nonatmospheric absorptions, although a solar contribution cannot be entirely ruled out. Two other weak bands centered at 2.278 +/- 0.002 and 2.296 +/- 0.002 micrometers may be at least partially mineralogic in origin. The data provide no conclusive identification of the mineralogy responsible for these absorption features. However, examination of terrestrial spectral libraries and previous moderate spectral resolution mineral studies indicates that the most likely origin of these features is either (bi)carbonate or (bi)sulfate anions in framework silicates or (Fe, Mg)-OH bonds in sheet silicates. If the bands are caused by phyllosilicate minerals, then an explanation must be found for the extremely narrow widths of the cation-OH features in the Mars spectra as compared to terrestrial minerals.

Astronomy↗