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1.
Daniel Lazard Noam Lahav J. B. Orenberg 《Origins of life and evolution of the biosphere》1987,17(2):135-148
Experimental results are presented for the verification of the first adsorption step of the ‘adsorbed template’ biogeochemical cycle, a simple model for a primitive prebiotic replication system. The adsorption of Poly-C, Poly-U, Poly-A, Poly-G, and 5′-AMP, 5′-GMP, 5′-CMP and 5′-UMP onto gypsum was studied. It was found that under the conditions of the experiment, the polymers have a very high affinity for the mineral surface, while the monomers adsorb much less efficiently. 相似文献
2.
Stephen Chan James Orenberg Noam Lahav 《Origins of life and evolution of the biosphere》1987,17(2):121-134
The adsorption of 5-AMP and 5-CMP was studied in saturated solutions of several soluble mineral salts (NaCl, Na2SO4, MgCl2·6H2O, MgSO4·7H2O, CaCl2·2H2O, CaSO4·2H2O, SrCl2·6H2O, SrSO4, and ZnSO4·7H2O) as a function of pH, ionic strength, and surface area of the solid salt. The adsorption shows a pH dependence; this can be correlated with the charge on the nucleotide molecule which is determined by the state of protonation of the N-1 nitrogen of 5-AMP or N-3 nitrogen of 5-CMP and the phosphate oxygens. The adsorption which results from the binding between the nucleotide molecule and the salt surface is proposed as being due to electrostatic forces. It was concluded that the adsorption was reversible in nature. The adsorption shows a strong dependence upon ionic strength and decreases with increasing ionic strength. Surface area is shown to be an important factor in evaluating and comparing the magnitude of adsorption of nucleotides onto various mineral salts. The implications of the results of the study are discussed in terms of the importance of soluble mineral salts as adsorption sites in the characterization of the adsorption reactions of an adsorbed template in biogeochemical cycles. 相似文献
3.
Oxidation of γ-Hydroxybutyrate to Succinic Semialdehyde by a Mitochondrial Pyridine Nucleotide-Independent Enzyme 总被引:2,自引:0,他引:2
Elaine E. Kaufman Thomas Nelson David Miller Noam Stadlan 《Journal of neurochemistry》1988,51(4):1079-1084
An antibody that inhibits over 95% of the cytosolic NADP+-dependent gamma-hydroxybutyrate (GHB) dehydrogenase activity of either rat brain or kidney was found to inhibit only approximately 50% of the conversion of [1-14C]GHB to 14CO2 by rat kidney homogenate. A similar result was obtained with sodium valproate, a potent inhibitor of GHB dehydrogenase. The mitochondrial fraction from rat brain and kidney was found to catalyze the conversion of [1-14C]GHB to 14CO2. The dialyzed mitochondrial fraction also catalyzed the oxidation of GHB to succinic semialdehyde (SSA) in a reaction that did not require added NAD+ or NADP+ and which was not inhibited by sodium valproate. The enzyme from the mitochondrial fraction which converts GHB to SSA appears to be distinct from the NADP+-dependent cytosolic oxidoreductase which catalyzes this reaction. 相似文献
4.
Zohar NJ 《Bioethics》1991,5(4):309-311
Several important issues are raised and illuminated in "Genetic Harm"; not least, in its detailed discussion of specific genetic disorders. In particular, it focuses on a type of disorder whose ill effects are not manifested at birth, but only at a later stage in life. The conclusion, with its significant implications for practice, seems quite valid: a moral duty should be recognized to genetically (or otherwise, if feasible) cure an embryo of that which is expected to (later) cause such prospective suffering. Yet the reasons given for that conclusion, as well as much of the argument throughout, concentrate on a debatable notion of "harm". On an alternate account -- drawn in terms of personal identity -- what makes the moral difference in this type of case is rather that the genotype manifests itself, and that a life-history begins, prior to (and thus independently of) any effects of the gene(s) we are called to alter. 相似文献
5.
Noam Lahav 《Origins of life and evolution of the biosphere》1993,23(5-6):329-344
The applicability of the RNA-world and co-evolution hypotheses to the study of the very first stages of the origin of life is discussed. The discussion focuses on the basic differences between the two hypotheses and their implications, with regard to the reconstruction methodology, ribosome emergence, balance between ribozymes and protein enzymes, and their major difficulties. Additional complexities of the two hypotheses, such as membranes and the energy source of the first reactions, are not treated in the present work.A central element in the proposed experimental strategies is the study of the catalytic activities of very small peptides and RNA-like oligomers, according to existing, as well as to yet-to-be-invented scenarios of the two hypotheses under consideration. It is suggested that the noveldirected molecular evolution technology, andmolecular computational modeling, can be applied to this research. This strategy is assumed to be essential for the suggested goal of future studies of the origin of life, namely, the establishment of a Primordial Darwinian entity. 相似文献
6.
Summary A model is proposed for a prebiotic environment in which concentration, condensation, and chemical evolution of biomolecules could have taken place. The main reactions expected of proteins, nucleic acids, lipids, and some of their precursors in this environment are examined.The model is based on our previously developed concept of a fluctuating system in which hydration and dehydration processes take place in a cyclic manner. In the present model, however, high concentrations of soluble salts, such as chlorides and sulfates, are taken into account, whereas previously a more or less salt-free system had been assumed. Thus the preponderance of surfaces of soluble salts is implied, even though sparingly soluble minerals, such as clay minerals or quartz, are also present.During the dehydration stage biomolecules tend to leave the solution and concentrate at certain microenvironments, such as in micelles and aggregates, at the liquid-gas surface and, possibly, at the emerging solid surfaces. Moreover, in these brines, and especially during the last stages of dehydration, high temperatures are attainable, which may enhance certain reactions between the organic molecules, and result in a net increase of condensation over degradation.In the dehydrated state, solid-state condensation and synthesis reactions are possible in which the surface of soluble salts may serve as a catalyst. Several reports in the literature support this hypothesis. Hydration brings about dissolution of the minerals and redistribution of the biomolecules. In such a system, evolutionary processes like those postulated by White (1980) and by Lahav and White (1980) are possible. Moreover, since several soluble salts of known geological occurrence are optically active in their crystalline state, the involvement of the model system in the selection and evolution of chiral organic compounds should also be considered. In addition, organic molecules in the above microenvironments are also expected to undergo selective interactions based on factors such as molecular pattern and chiral recognition and hydrophobicity. The proposed system emphasizes the need to develop the theoretical background and experimental methods for the study of interactions among biomolecules in the presence of high salt concentrations and solid surfaces of soluble salts, as well as interactions between the biomolecules and these surfaces. 相似文献
7.
We present a simple, efficient system for preparative polyacrylamide gel electrophoresis (PAGE) in sodium dodecyl sulfate. The instrument features a novel sample collection assembly which is fitted directly onto the bottom of the gel cylinder. Buffer pumped uniformly upward through a porous plastic disk from the lower tray sweeps the emerging sample into a collection system with high efficiency. Measures which prevent the destruction of tryptophan residues and the blockage of α-amino groups observed in electrophoresed polypeptides are described. 相似文献
8.
Einat Adar Moshe Inbar Shira Gal Noam Doron Zhi-Qiang Zhang Eric Palevsky 《Experimental & applied acarology》2012,58(4):341-357
In previous studies plant feeding behavior of plant- and non-plant feeding phytoseiids was never examined directly. Moreover, in these studies the cheliceral morphology of phytoseiids was not associated with their ability to feed on plants. In the present study, we monitored the plant-feeding behavior of Euseius scutalis and Amblyseius swirskii. Only E. scutalis was observed penetrating the leaf surface with the movable digit and feeding. Second, using a dye and coloring the gut as an indicator for feeding, we found that E. scutalis pierced an artificial membrane and fed whereas A. swirskii did not. Finally, to identify morphological characteristics typical of plant feeders versus non-plant feeders, we used scanning electron microscopy to examine the adaxial (inner) profile of the chelicerae in 13 phytoseiid species. The only parameter that distinguished between plant- and non-plant feeders was the ratio of the dorsal perimeter length of the fixed digit to the ventral perimeter length of the movable digit. Plant-feeders were characterized by ratio values greater than one whereas the values for non plant-feeders were lower than one. We suggest that a shorter and less curved movable digit, expressed by a high ratio, will facilitate the penetration of the leaf surface. Cheliceral traits proposed here as typical of plant feeders, were observed for five genera, indicating that plant-feeding may be more common in the Phytoseiidae than previously reported. We propose that the ability to feed on plants be added as a cross type trait of phytoseiid life-style types. 相似文献
9.
10.
Froy O Zilberberg N Gordon D Turkov M Gilles N Stankiewicz M Pelhate M Loret E Oren DA Shaanan B Gurevitz M 《The Journal of biological chemistry》1999,274(9):5769-5776
Scorpion neurotoxins of the excitatory group show total specificity for insects and serve as invaluable probes for insect sodium channels. However, despite their significance and potential for application in insect-pest control, the structural basis for their bioactivity is still unknown. We isolated, characterized, and expressed an atypically long excitatory toxin, Bj-xtrIT, whose bioactive features resembled those of classical excitatory toxins, despite only 49% sequence identity. With the objective of clarifying the toxic site of this unique pharmacological group, Bj-xtrIT was employed in a genetic approach using point mutagenesis and biological and structural assays of the mutant products. A primary target for modification was the structurally unique C-terminal region. Sequential deletions of C-terminal residues suggested an inevitable significance of Ile73 and Ile74 for toxicity. Based on the bioactive role of the C-terminal region and a comparison of Bj-xtrIT with a Bj-xtrIT-based model of a classical excitatory toxin, AaHIT, a conserved surface comprising the C terminus is suggested to form the site of recognition with the sodium channel receptor. 相似文献