Amplification mechanisms

Many low weight compounds produced by microor-ganism-like formylated peptides as well as endogenous mediators are chemotactic for leukocytes and promote the inflammatory process. The main endogenous compounds are listed in Table 1 and are derived from activated plasma protein cascades that function as amplification mechanisms, are performed and released from activated cells or are de novo synthesized on demand by cells participating in or being affected by inflammatory events. The major modulators of leukocyte adhesion to endothelial cells are listed in Table 2. 

Gilfillan AM, PeavyRD, Metcalfe DD Amplification mechanisms for the enhancement of antigen-mediated mast cell activation. Immunol Res 2009 43 15-24. 

By taking into account the latest results on the behaviour of systems far away from equilibrium, Kondepudi and Nelson (1985) were able to show by calculation that L-amino acids are slightly favoured. There is a very tiny stabilisation effect due to the weak interaction amplification mechanisms cause this effect to reach 98% of the probability that L-enantiomers of amino acids are favoured for incorporation into polymers. The amplification mechanisms are explained by the thermodynamics of irreversible systems. 

Adessi, C., Matton, G., Ayala, G., Turcatd, G., Mermod, J.-J., Mayer, P., and Kawashima, E. (2000) Solid phase DNA amplification Characterisation of primer attachment and amplification mechanisms. Nucleic Acids Res. 28, e87. 

Dore K, Leclerc M, Boudreau D (2006) Investigation of a fluorescence signal amplification mechanism used for the direct molecular detection of nucleic acids. J Fluoresc 16 259-265... 

These schemes have been frequently suggested [105-107] as possible mechanisms to achieve the chirally pure starting point for prebiotic molecular evolution toward our present homochiral biopolymers. Demonstrably successftd amplification mechanisms are the spontaneous resolution of enantiomeric mixtures under race-mizing conditions, [509 lattice-controlled solid-state asymmetric reactions, [108] and other autocatalytic processes. [103, 104] Other experimentally successful mechanisms that have been proposed for chirality amplification are those involving kinetic resolutions [109] enantioselective occlusions of enantiomers on opposite crystal faces, [110] and lyotropic liquid crystals. [Ill] These systems are interesting in themselves but are not of direct prebiotic relevance because of their limited scope and the specialized experimental conditions needed for their implementation. 

Schimke RT (1986) Methotrexate resistance and gene amplification. Mechanisms and implications. Cancer 57 1912-1917... 

The efficiency of energy conversion in the polymers, i.e. how much the change in shape of the chain is induced by a photon, is, however, rather low. They need many photons and a high content of pendant photochromic chromophores to induce a large conformation change. To make a sensitive photo-responsive polymer, i.e. one which responds more efficiently to fewer photons, it is necessary to introduce an amplification mechanism to the system. One possible way of achieving this is to utilize the phase transition of polymers [7,8]. 

The special role of three-dimensionality in this field amplification mechanism becomes especially clear when it is compared with an externally similar cycle proposed earlier by the Swedish scientist H. Alfven (1950) [68]. In the Alfven cycle (Fig. 3, borrowed from [68]), an initial tube (1) is stretched, and opposite sides of the ring (2), which is filled with magnetic field lines,... 

Chabre, M., Trigger and amplification mechanisms in visual phototransduction. Ann. Rev. Biophysics Biophysical Chem. 14 331, 1985. A review covering the structure of rhodop-... 

Balboa M. A., Perez R., and Balsinde J. (2003). Amplification mechanisms of inflammation Paracrine stimulation of arachidonic acid mobilization by secreted phospholipase A2 is regulated by cytosolic phospholipase A2-derived hydroperoxyeicosatetraenoic acid. J. Immunol. 

As outlined in a later section, dimer formation is believed to play an essential role in the chiral amplification mechanism. Since the thermodynamic stabilities as well as the kinetics of formation of the dimers depend on their structural properties, variations in the amplification capacity by taking different aldehyde substrates may appear rational from this point of view. 

Since the historical PV weak force origin /3-decay experiment of 60Co [ 106], theoreticians presumed that the tiny parity violating WNC at molecular and subatomic levels may also allow a distinction between mirror image molecules at the macroscopic level as well. This is because PV-WNC at the molecular level may be a candidate for the homochiral scenario under terrestrial and extraterrestrial conditions [1,2,104,109-118]. The WNC, however, did not induce any observable PV effects between enantiomers in their ground states because of the minuscule PV energy difference (PVED) of 10 19 eV and/or negligibly small 10 - % ee in racemates. Theoreticians also proposed several possible amplification mechanisms at reproducible detection levels within laboratory time scales and at terrestrial locations [113,117,118]. 

The macromolecular helicity induced in poly(phenylacetylene)s 28-30 (Fig. 14) upon complexation with chiral amines is dynamic in nature, and therefore, the ICD due to the helical chirality immediately disappears when exposed to a stronger acid such as trifluoroacetic acid. However, during the intensive exploration of the helicity induction and chirality amplification mechanism of the poly(phenylacetylene)s, such an induced helical chirality of 28-30 by an optically active amine such as (R)-39 has been found to be maintained, namely memorized , when the chiral amine is completely removed and replaced by various achiral amines, for example, 71 and 72 for 28 and diamines such as ethylenediamine for 29 and 30 in... 

The olfactory epithelium is composed of basal, neuronal (olfactory), and susten-tacular (support) cells (Figure 27.3). The portion of each olfactory cell that responds to the olfactory chemical stimuli is the cilia. The odorant substance first diffuses into the mucus that covers the cilia and then binds to specific receptor proteins in the membrane of each cilium. Next, receptor activation by the odorant activates a multiple molecules of the G-protein complex in the olfactory epithelial cell. This, in turn, activates adenylyl cyclase inside the olfactory cell membrane, which, in turn, causes formation of a greater multitude of cAMP molecules. Finally, the cAMP molecules trigger the opening of yet an even greater multitude of sodium ion channels. This amplification mechanism accounts for the exquisite sensitivity of the olfactory neurons to extremely small amounts of odorant. The olfactory epithelium is an important target of certain inhaled toxicants. Certain metals, solvents, proteins, and viruses are transported to the brain via transport from the olfactory epithelium to the olfactory tract and exert neurotoxicity. 

The cpl-induced asymmetry in photoreactions as described in Sec. B. of this chapter is not very pronounced. In order to obtain ees in excess of a few percent, photodestruction must be chosen and most of the reactant material must be sacrificed. Therefore amplification mechanisms for all types of cpl-induced asymmetric photoreactions would be highly desirable. Autocatalysis, i.e., an asymmetric synthesis where a chiral product acts as a catalyst for its own production [128], and autoinduction, i.e., the stimulation of a chiral catalyst by a chiral product [44,129], are options. Autocatalytic systems that will tilt to one enantiomeric side were introduced by Frank [130] and Seelig [131]. 

If direct cpl-induced one-photon photochemistry should be the source of homochirality, the assumption of the activity of amplification mechanisms is necessary. But cpl photolysis is only one of the mechanisms discussed for symmetry breaking and creation of homochirality. Bonner [11] and Feringa and van Delden [61] reviewed this topic and give sources for further information. On the... 

Asymmetric photochemistry is intensively discussed as one of the possibilities for the origin of the observed homochirality of amino acids and saccharides in biological systems. There is no doubt that also in natural environments cpl exists and may create an enantiomeric excess in a photoreaction, but according to all knowledge, there must be an amplification mechanism, which has not yet been safely detected. 

Photoresponsive polymers so far described change their properties in proportion to the number of photons that they absorb. Thus, when they contain more photo-chromic chromophores, which undergo an isomerization by absorbing a definite number of photons depending on the quantum yield, their properties change more. To make a sensitive photoresponsive polymer, i.e. one which responds more effidently to a fewer photons, we have to introduce an amplification mechanism into the system. A convenient way to achieve this end is to utilize the phase transition of polymers. 

The potential for amplification of airway responses is intriguing. Mast cell products released by specific antigen-IgE interactions could stimulate C-fibers to release tachykinins, and these tachykinins could then stimulate the mast cells that fell within the dendritic network of the particular nerve involved. Therefore, local antigen-induced stimulation of mast cells could spread far beyond the diffusion distance for the antigen in question. The specific relevance of this proposed amplification mechanism to human disease has not been evaluated. 

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