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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Carbon and Oxygen Budgets of Hypersaline Cyanobacterial Mats: Effects of Tidal Cycle and Temperature

The hierarchical organization of microbial ecosystems determines the rates of processes that shape Earth#s environment, define the stage upon which major evolutionary events occurred, and create biosignatures in sediments and atmospheres. In cyanobacterial mats, oxygenic photosynthesis provides energy, organic substrates and oxygen to the ecosystem. Incident light changes with depth in the mat, both in intensity and spectral composition, and counteracting gradients of oxygen and sulfide shape the chemical microenvironment. A combination of benefits and hazards of light, oxygen and sulfide promotes the allocation of the various essential mat processes between light and dark periods and to various depths in the mat. Microbiota produce hydrogen, small organic acids, and nitrogen and sulfur species. Such compounds fuel a flow of energy and electrons in these ecosystems and thus shape interactions between groups of microorganisms. Coordinated observations of population distribution, abundance, and activity for an entire community are making fundamental questions in ecology accessible. These questions address those factors that sustain the remarkable diversity of microorganisms that are now being revealed by molecular techniques. These questions also target the processes that shape the various kinds of biosignatures that we will seek, both in ancient rocks from Earth and Mars, and in atmospheres of distant planets beyond our Solar System.

David J Des Marais↗
NASA NTRS2004

Putting us on the Map: Remote Sensing Investigation of the Ancient Maya Landscape

A common problem for archaeologists studying ancient settlement in the Maya Lowlands is overcoming the dense vegetation in order to obtain an accurate regional perspective of the presence of archaeological sites, their exact locations and their overall extents. Most often this is done by extensive ground surveys in which many individuals chop parallel paths through the vegetation in search of sites. Once a site is found an effort is made to mark its location on a regional map and to explore its perimeter. Obtaining locational information has been made dramatically easier in recent years with the advent of improved Global Positioning Systems (GPS), however the process of initial identification of sites and the determination of their borders is exceedingly labor intensive and has remained relatively unchanged since the beginning of settlement surveys in the region in the 1950's. Currently, we are revolutionizing settlement survey in the Maya Lowlands by using remotely sensed data from IKONOS, Quickbird, and Eol, satellites. The Ancient Maya built their cities, towns and even their smallest hamlets using excavated limestone and lime plasters. We propose that the decay of these structures provides a unique microenvironment for the growth of vegetation as the levels of moisture and nutrition within the ruins vary substantially from those in the surrounding forest. These microenvironmental differences on the ground are likewise represented by compositional differences in the forest canopy both in the species present and in leaf color (representing moisture/nutritional stress) visible through the analysis of high- resolution satellite data. In this way the detailed analysis of forest composition can reveal a detailed picture of the ancient settlements that lie beneath it. Preliminary examinations using this technique have been very successful and we are refining these techniques in order to efficiently comprehend the details of Ancient Maya settlement in the Lowlands.

Sever, Thomas L.↗
NASA NTRS2004

Electrochemical and Hydrodynamic Interferences on the Performances of an Oxygen Microsensor with Built-in Electrochemical Microactuator

A concept of novel electrochemical in situ self-calibration technique for an oxygen microsensor has been proposed to devise a convenient calibration method without an externally coupled apparatus. Systemic investigations on the influences of various electrochemical (pH) and hydrodynamic (solution stirring) conditions on the proposed microsensor performances are presented. The results suggest that: 1) The calibrating microenvironments can be manipulated with carefully engineered sensor designs and optimized generating signals; 2) The external oxygen permeable membrane is needed to minimize the electrochemical and hydrodynamic interferences.

Kim, Chang-Soo↗
NASA NTRS2003

Methane Production by Microbial Mats Under Low Sulfate Concentrations

Cyanobacterial mats collected in hypersaline salterns were incubated in a greenhouse under low sulfate concentrations ([SO4]) and examined for their primary productivity and emissions of methane and other major carbon species. Atmospheric greenhouse warming by gases such as carbon dioxide and methane must have been greater during the Archean than today in order to account for a record of moderate to warm paleoclemates, despite a less luminous early sun. It has been suggested that decreased levels of oxygen and sulfate in Archean oceans could have significantly stimulated microbial methanogenesis relative to present marine rates, with a resultant increase in the relative importance of methane in maintaining the early greenhouse. We maintained modern microbial mats, models of ancient coastal marine communities, in artificial brine mixtures containing both modern [SO4=] (ca. 70 mM) and "Archean" [SO4] (less than 0.2 mM). At low [SO4], primary production in the mats was essentially unaffected, while rates of sulfate reduction decreased by a factor of three, and methane fluxes increased by up to ten-fold. However, remineralization by methanogenesis still amounted to less than 0.4 % of the total carbon released by the mats. The relatively low efficiency of conversion of photosynthate to methane is suggested to reflect the particular geometry and chemical microenvironment of hypersaline cyanobacterial mats. Therefore, such mats w-ere probably relatively weak net sources of methane throughout their 3.5 Ga history, even during periods of low- environmental levels oxygen and sulfate.

Bebout, Brad M.↗
NASA NTRS2003

Fundamental space radiobiology

The unique feature of the space radiation environment is the dominance of high-energy charged particles (HZE or high LET radiation) emitted by the Sun and galactic sources, or trapped in the Van Allen radiation belts. These charged particles present a significant hazard to space flight crews, and accelerator-based experiments are underway to quantify the health risks due to unavoidable radiation exposure. There are three principal properties of charged particles that distinguish them from conventional radiation, i.e. gamma rays and x-rays. First, they have a defined range in matter rather than an exponential absorption profile. Second, they undergo nuclear reactions to produce secondary particles. Third, and most important, they deposit their energy along well-defined linear paths or tracks rather than diffuse fields. The structured energy deposition pattern interacts on multiple scales with the biological structures of DNA, cells and tissues to produce correlated patterns of damage that evade repair systems. Traditional concepts of dose and its associated normalization parameter, RBE (relative biological effectiveness), break down under experimental scrutiny, and probabilistic models of risk based on the number of particle traversals per cell may be more appropriate. Unique patterns of DNA damage, gene expression, mobilization of repair proteins, activation of cytokines and remodeling of cellular microenvironment are observed following exposure to high LET radiation. At low levels of exposure the communication of bioactive substances from irradiated to unirradiated "bystander" cells can amplify the damage and cause a significant deviation from linearity in dose vs. response relations. Under some circumstances, there is even a multigenerational delay in the expression of radiation-induced genetic damage (genomic instability) which is not strictly dose dependent. These issues and the experimental evidence derived from ground based experiments at particle accelerators are presented along with speculation about how modified inertial conditions might perturb homeostatic responses to radiation to further complicate risk assessment for space flight.

NASA Discipline Radiation Health↗
NASA NTRS2003

Interactions between neutrophils and macrophages promote macrophage killing of rat muscle cells in vitro

Current evidence indicates that the physiological functions of inflammatory cells are highly sensitive to their microenvironment, which is partially determined by the inflammatory cells and their potential targets. In the present investigation, interactions between neutrophils, macrophages and muscle cells that may influence muscle cell death are examined. Findings show that in the absence of macrophages, neutrophils kill muscle cells in vitro by superoxide-dependent mechanisms, and that low concentrations of nitric oxide (NO) protect against neutrophil-mediated killing. In the absence of neutrophils, macrophages kill muscle cells through a NO-dependent mechanism, and the presence of target muscle cells causes a three-fold increase in NO production by macrophages, with no change in the concentration of inducible nitric oxide synthase. Muscle cells that are co-cultured with both neutrophils and macrophages in proportions that are observed in injured muscle show cytotoxicity through a NO-dependent, superoxide-independent mechanism. Furthermore, the concentration of myeloid cells that is necessary for muscle killing is greatly reduced in assays that use mixed myeloid cell populations, rather than uniform populations of neutrophils or macrophages. These findings collectively show that the magnitude and mechanism of muscle cell killing by myeloid cells are modified by interactions between muscle cells and neutrophils, between muscle cells and macrophages and between macrophages and neutrophils.

Non-NASA Center↗
NASA NTRS2002

Mechanical signaling and the cellular response to extracellular matrix in angiogenesis and cardiovascular physiology

Great advances have been made in the identification of the soluble angiogenic factors, insoluble extracellular matrix (ECM) molecules, and receptor signaling pathways that mediate control of angiogenesis--the growth of blood capillaries. This review focuses on work that explores how endothelial cells integrate these chemical signals with mechanical cues from their local tissue microenvironment so as to produce functional capillary networks that exhibit specialized form as well as function. These studies have revealed that ECM governs whether an endothelial cell will switch between growth, differentiation, motility, or apoptosis programs in response to a soluble stimulus based on its ability to mechanically resist cell tractional forces and thereby produce cell and cytoskeletal distortion. Transmembrane integrin receptors play a key role in this mechanochemical transduction process because they both organize a cytoskeletal signaling complex within the focal adhesion and preferentially focus mechanical forces on this site. Molecular filaments within the internal cytoskeleton--microfilaments, microtubules, and intermediate filaments--also contribute to the cell's structural and functional response to mechanical stress through their role as discrete support elements within a tensegrity-stabilized cytoskeletal array. Importantly, a similar form of mechanical control also has been shown to be involved in the regulation of contractility in vascular smooth muscle cells and cardiac myocytes. Thus, the mechanism by which cells perform mechanochemical transduction and the implications of these findings for morphogenetic control are discussed in the wider context of vascular development and cardiovascular physiology.

Non-NASA Center↗
NASA NTRS2002

Avian dark cells

Dark cells (DCs) of mammalian and non-mammalian species help to maintain the homeostasis of the inner ear fluids in vivo. Although the avian cochlea is straight and the mammalian cochlea is coiled, no significant difference in the morphology and/or function of mammalian and avian DCs has been reported. The mammalian equivalent of avian DCs are marginal cells and are located in the stria vascularis along a bony sheet. Avian DCs hang free from the tegmentum vasculosum (TV) of the avian lagena between the perilymph and endolymph. Frame averaging was used to image the fluorescence emitted by several fluorochromes applied to freshly isolated dark cells (iDCs) from chickens (Gallus domesticus) inner ears. The viability of iDCs was monitored via trypan blue exclusion at each isolation step. Sodium Green, BCECF-AM, Rhodamine 123 and 9-anthroyl ouabain molecules were used to test iDC function. These fluorochromes label iDCs ionic transmembrane trafficking function, membrane electrogenic potentials and Na+/K+ ATPase pump's activity. Na+/K+ ATPase pump sites, were also evaluated by the p-nitrophenyl phosphatase reaction. These results suggest that iDCs remain viable for several hours after isolation without special culturing requirements and that the number and functional activity of Na+/K+ ATPase pumps in the iDCs were indistinguishable from in vivo DCs. Primary cultures of freshly iDCs were successfully maintained for 28 days in plastic dishes with RPMI 1640 culture medium. The preparation of iDCs overcomes the difficulty of DCs accessability in vivo and the unavoidable contamination that rupturing the inner ear microenvironments induces.

NASA Discipline Neuroscience↗
NASA NTRS1999

Oxygen-depleted zones inside reproductive structures of Brassicaceae: implications for oxygen control of seed development

Growth of Arabidopsis thaliana (L.) Heynh. in decreasing oxygen partial pressures revealed a linear decrease in seed production below 15 kPa, with a complete absence of seed production at 2.5 kPa oxygen. This control of plant reproduction by oxygen had previously been attributed to an oxygen effect on the partitioning between vegetative and reproductive growth. However, plants grown in a series of decreasing oxygen concentrations produced progressively smaller embryos that had stopped developing at progressively younger stages, suggesting instead that their growth is limited by oxygen. Internal oxygen concentrations of buds, pistils, and developing siliques of Brassica rapa L. and siliques of Arabidopsis were measured using a small-diameter glass electrode that was moved into the structures using a micromanipulator. Oxygen partial pressures were found to be lowest in the developing perianth (11.1 kPa) and pistils (15.2 kPa) of the unopened buds. Pollination reduced oxygen concentration inside the pistils by 3 kPa after just 24 h. Inside Brassica silique locules, partial pressures of oxygen averaged 12.2 kPa in darkness, and increased linearly with increasing light levels to 16.2 kPa. Measurements inside Arabidopsis siliques averaged 6.1 kPa in the dark and rose to 12.2 kPa with light. Hypoxia in these microenvironments is postulated to be the point of control of plant reproduction by oxygen.

Non-NASA Center↗
NASA NTRS1998

Changes in Arabidopsis leaf ultrastructure, chlorophyll and carbohydrate content during spaceflight depend on ventilation

Leaf structure and function under spaceflight conditions have received little study despite their important implications for biological life support systems using plants. Previous reports described disruption of the membrane apparatus for photosynthesis and a general decrease in carbohydrate content in foliage. During a series of three short-duration experiments (Chromex-03, -04, -05) on the US space shuttle (STS-54, STS-51, STS-68), we examined Arabidopsis thaliana leaves. The plants were at the rosette stage at the time of loading onto the space shuttle, and received the same light, temperature, carbon dioxide and humidity regimes in the orbiter as in ground controls. The experiments differed according to the regime provided in the headspace around the plants: this was either sealed (on mission STS-54); sealed with high levels of carbon dioxide (on mission STS-51) or vented to the cabin air through a filtration system (on mission STS-68). Immediately post-flight, leaf materials were fixed for microscopy or frozen in liquid nitrogen for subsequent analyses of chlorophyll and foliar carbohydrates. At the ultrastructural level, no aberrations in membrane structure were observed in any of the experiments. When air-flow was provided, plastids developed large starch grains in both spaceflight and ground controls. In the experiments with sealed chambers, spaceflight plants differed from ground controls with regard to measured concentrations of carbohydrate and chlorophyll, but the addition of airflow eliminated these differences. The results point to the crucial importance of consideration of the foliage microenvironment when spaceflight effects on leaf structure and metabolism are studied.

STS-51 Shuttle Project↗
NASA NTRS1997

Whiting events: biogenic origin due to the photosynthetic activity of cyanobacterial picoplankton

An annual whiting event occurs each year in late May to early June in Fayetteville Green Lake, New York. The initiation of this event correlates with exponential growth of the Synechococcus population within the lake. Synechococcus is the dominant (by approximately 4 orders of magnitude) autotrophic organism owing to the oligotrophic condition of the lake. The delta 13C values of the dissolved inorganic C range seasonally from -9.5% in winter to -6.2% in summer due to photosynthetic activity. Calcite precipitates principally in the microenvironment surrounding Synechococcus because of a photosynthetically driven alkalization process and the availability of the cells as nucleation sites. This calcite has a heavier delta 13C value (>4%) than does the dissolved inorganic C of the lake water owing to the cells' preferential uptake of 12C. A conceptual model suggests that photosynthetic activity and cell surface chemistry, together with the substantial surface area that arises from the great abundance of micron-sized cells, allow Synechococcus to dominate the annual whiting events in Fayetteville Green Lake.

NASA Center ARC↗
NASA NTRS1989

Microfossils from silicified stromatolitic carbonates of the Upper Proterozoic Limestone-Dolomite 'Series', central East Greenland

Silicified flake conglomerates and in situ stratiform stromatolites of the Upper Proterozoic (c. 700-800 Ma) Limestone-Dolomite 'Series', central East Greenland, contain well preserved microfossils. Five stratigraphic horizons within the 1200 m succession contain microbial mat assemblages, providing a broad palaeontological representation of late Proterozoic peritidal mat communities. Comparison of assemblages demonstrates that the taxonomy and diversity of mat builder, dweller, and allochthonous populations all vary considerably within and among horizons. The primary mat builder in most assemblages is Siphonophycus inornatum, a sheath-forming prokaryote of probable but not unequivocally established cyanobacterial affinities. An unusual low diversity unit in Bed 17 is dominated by a different builder, Tenuofilum septatum, while a thin cryptalgal horizon in Bed 18 is built almost exclusively by Siphonophycus kestron. Although variable taphonomic histories contribute to observed assemblage variation, most differences within and among horizons appear to reflect the differential success or failure of individual microbial populations in colonizing different tidal flat microenvironments. Twenty-two taxa are recognized, of which two are described as new: Myxococcoides stragulescens n.sp. and Scissilisphaera gradata n. sp.

NASA Discipline Number 52-30↗
NASA NTRS2000

Quantitative image analysis of laminin immunoreactivity in skin basement membrane irradiated with 1 GeV/nucleon iron particles

We previously reported that laminin immunoreactivity in mouse mammary epithelium is altered shortly after whole-body irradiation with 0.8 Gy from 600 MeV/nucleon iron ions but is unaffected after exposure to sparsely ionizing radiation. This observation led us to propose that the effect could be due to protein damage from the high ionization density of the ion tracks. If so, we predicted that it would be evident soon after radiation exposure in basement membranes of other tissues and would depend on ion fluence. To test this hypothesis, we used immunofluorescence, confocal laser scanning microscopy, and image segmentation techniques to quantify changes in the basement membrane of mouse skin epidermis. At 1 h after exposure to 1 GeV/nucleon iron ions with doses from 0.03 to 1.6 Gy, neither the visual appearance nor the mean pixel intensity of laminin in the basement membrane of mouse dorsal skin epidermis was altered compared to sham-irradiated tissue. This result does not support the hypothesis that particle traversal directly affects laminin protein integrity. However, the mean pixel intensity of laminin immunoreactivity was significantly decreased in epidermal basement membrane at 48 and 96 h after exposure to 0.8 Gy 1 GeV/nucleon iron ions. We confirmed this effect with two additional antibodies raised against affinity-purified laminin 1 and the E3 fragment of the long-arm of laminin 1. In contrast, collagen type IV, another component of the basement membrane, was unaffected. Our studies demonstrate quantitatively that densely ionizing radiation elicits changes in skin microenvironments distinct from those induced by sparsely ionizing radiation. Such effects may might contribute to the carcinogenic potential of densely ionizing radiation by altering cellular signaling cascades mediated by cell-extracellular matrix interactions.

Non-NASA Center↗
NASA NTRS1999

Phototrophs in high-iron-concentration microbial mats: physiological ecology of phototrophs in an iron-depositing hot spring

At Chocolate Pots Hot Springs in Yellowstone National Park the source waters have a pH near neutral, contain high concentrations of reduced iron, and lack sulfide. An iron formation that is associated with cyanobacterial mats is actively deposited. The uptake of [(14)C]bicarbonate was used to assess the impact of ferrous iron on photosynthesis in this environment. Photoautotrophy in some of the mats was stimulated by ferrous iron (1.0 mM). Microelectrodes were used to determine the impact of photosynthetic activity on the oxygen content and the pH in the mat and sediment microenvironments. Photosynthesis increased the oxygen concentration to 200% of air saturation levels in the top millimeter of the mats. The oxygen concentration decreased with depth and in the dark. Light-dependent increases in pH were observed. The penetration of light in the mats and in the sediments was determined. Visible radiation was rapidly attenuated in the top 2 mm of the iron-rich mats. Near-infrared radiation penetrated deeper. Iron was totally oxidized in the top few millimeters, but reduced iron was detected at greater depths. By increasing the pH and the oxygen concentration in the surface sediments, the cyanobacteria could potentially increase the rate of iron oxidation in situ. This high-iron-content hot spring provides a suitable model for studying the interactions of microbial photosynthesis and iron deposition and the role of photosynthesis in microbial iron cycling. This model may help clarify the potential role of photosynthesis in the deposition of Precambrian banded iron formations.

NASA Discipline Exobiology↗
NASA NTRS1998

Expression of extracellular calcium (Ca2+o)-sensing receptor in human peripheral blood monocytes

The calcium-sensing receptor (CaR) is a G protein-coupled receptor playing key roles in extracellular calcium ion (Ca2+o) homeostasis in parathyroid gland and kidney. Macrophage-like mononuclear cells appear at sites of osteoclastic bone resorption during bone turnover and may play a role in the "reversal" phase of skeletal remodeling that follows osteoclastic resorption and precedes osteoblastic bone formation. Bone resorption produces substantial local increases in Ca2+o that could provide a signal for such mononuclear cells present locally within the bone marrow microenvironment. Indeed, previous studies by other investigators have shown that raising Ca2+o either in vivo or in vitro stimulated the release of interleukin-6 (IL-6) from human peripheral blood monocytes, suggesting that these cells express a Ca2+o-sensing mechanism. In these earlier studies, however, the use of reverse transcription-polymerase chain reaction (RT-PCR) failed to detect transcripts for the CaR previously cloned from parathyroid and kidney in peripheral blood monocytes. Since we recently found that non-specific esterase-positive, putative monocytes isolated from murine bone marrow express the CaR, we reevaluated the expression of this receptor in human peripheral blood monocytes. Immunocytochemistry, flow cytometry, and Western blot analysis, performed using a polyclonal antiserum specific for the CaR, detected CaR protein in human monocytes. In addition, the use of RT-PCR with CaR-specific primers, followed by nucleotide sequencing of the amplified products, identified CaR transcripts in the cells. Therefore, taken together, our data show that human peripheral blood monocytes possess both CaR protein and mRNA very similar if not identical to those expressed in parathyroid and kidney that could mediate the previously described, direct effects of Ca2+o on these cells. Furthermore, since mononuclear cells isolated from bone marrow also express the CaR, the latter might play some role in the "reversal" phase of bone remodeling, sensing local changes in Ca2+o resulting from osteoclastic bone resorption and secreting osteotropic cytokines or performing other Ca2+o-regulated functions that contribute to the control of bone turnover.

NASA Discipline Musculoskeletal↗
NASA NTRS1997

Biodiversity within hot spring microbial mat communities: molecular monitoring of enrichment cultures

We have begun to examine the basis for incongruence between hot spring microbial mat populations detected by cultivation or by 16S rRNA methods. We used denaturing gradient gel electrophoresis (DGGE) to monitor enrichments and isolates plated therefrom. At near extincting inoculum dilutions we observed Chloroflexus-like and cyanobacterial populations whose 16S rRNA sequences have been detected in the 'New Pit' Spring Chloroflexus mat and the Octopus Spring cyanobacterial mat. Cyanobacterial populations enriched from 44 to 54 degrees C and 56 to 63 degrees C samples at near habitat temperatures were similar to those previously detected in mat samples of comparable temperatures. However, a lower temperature enrichment from the higher temperature sample selected for the populations found in the lower temperature sample. Three Thermus populations detected by both DGGE and isolation exemplify even more how enrichment may bias our view of community structure. The most abundant population was adapted to the habitat temperature (50 degrees C), while populations adapted to 65 degrees C and 70 degrees C were 10(2)- and 10(4)-fold less abundant, respectively. However, enrichment at 70 degrees C favored the least abundant strain. Inoculum dilution and incubation at the habitat temperature favored the more numerically relevant populations. We enriched many other aerobic chemoorganotrophic populations at various inoculum dilutions and substrate concentrations, most of whose 16S rRNA sequences have not been detected in mats. A common feature of numerically relevant cyanobacterial, Chloroflexus-like and aerobic chemorganotrophic populations, is that they grow poorly and resist cultivation on solidified medium, suggesting plating bias, and that the medium composition and incubation conditions may not reflect the natural microenvironments these populations inhabit.

Non-NASA Center↗
NASA NTRS2004

Putting Us on the Map: Remote Sensing Investigation of the Ancient Maya Landscape

A common problem for archaeologists studying ancient settlement in the Maya Lowlands is overcoming the dense vegetation in order to obtain an accurate regional perspective of the presence of archaeological sites, their exact locations and their overall extents. Most often this is done by extensive ground surveys in which many individuals chop parallel paths through the vegetation in search of sites. Once a site is found an effort is made to mark its location on a regional map and to explore its perimeter. Obtaining locational information has been made dramatically easier in recent years with the advent of improved Global Positioning Systems (GPS), however the process of initial identification of sites and the determination of their borders is exceedingly labor intensive and has remained relatively unchanged since the beginning of settlement surveys in the region in the 1950 s. Currently, we are revolutionizing settlement survey in the Maya Lowlands by using remotely sensed data from IKONOS, Quickbird, and Eo 1, satellites as well as airborne AIRSAR radar data. The Ancient Maya built their cities, towns and even their smallest hamlets using excavated limestone and lime plasters. We propose that the decay of these structures provides a unique microenvironment for the growth of vegetation as the levels of moisture and nutrition within the ruins vary substantially from those in the surrounding forest. These microenvironmental differences on the ground are likewise represented by compositional differences in the forest canopy both in the species present and in leaf color (representing moisture/nutritional stress) visible through the analysis of high-resolution satellite data. In this way the detailed analysis of forest composition can reveal a detailed picture of the ancient settlements that lie beneath it. Preliminary examinations using this technique have been very successful and we are refining these techniques in order to efficiently comprehend the details of Ancient Maya settlement in the Lowlands.

Sever, Thomas L.↗
NASA NTRS1994

Production of RNA by a polymerase protein encapsulated within phospholipid vesicles

Catalyzed polymerization reactions represent a primary anabolic activity of all cells. It can be assumed that early cells carried out such reactions, in which macromolecular catalysts were encapsulated within some type of boundary membrane. In the experiments described here, we show that a template-independent RNA polymerase (polynucleotide phosphorylase) can be encapsulated in dimyristoyl phosphatidylcholine vesicles without substrate. When the substrate adenosine diphosphate (ADP) was provided externally, long-chain RNA polymers were synthesized within the vesicles. Substrate flux was maximized by maintaining the vesicles at the phase transition temperature of the component lipid. A protease was introduced externally as an additional control. Free enzyme was inactivated under identical conditions. RNA products were visualized in situ by ethidium bromide fluorescence. The products were harvested from the liposomes, radiolabeled, and analyzed by polyacrylamide gel electrophoresis. Encapsulated catalysts represent a model for primitive cellular systems in which an RNA polymerase was entrapped within a protected microenvironment.

Non-NASA Center↗