The primary event

In 1958, a new intermediate in the bleaching sequence of rhodopsin was discovered, the liquid air illuminated rhodopin [93]. This red-shifted transient (Amax =543 nm) could be observed when cattle rhodopsin was irradiated in aqueous-glycerol 

Irradiation of rhodopsin with blue light (437 nm) at 77 K gave a photostationary mixture containing in addition to rhodopsin (33%) and isorhodopsin (16%) about 51 % of batho intermediate. This process was found to be thermally irreversible but photochemically reversible. Indeed, irradiation of bathorhodopsin with red light ( 650 nm) gave mainly rhodopsin and isorhodopsin. Irradiation of isorhodopsin, which contains a 9-cis chromophore, afforded the same batho product as the one obtained by irradiation of rhodopsin  

The observation of this common batho product was used as the strongest argument in favor of the involvement of cis to trans isomerization in the primary event. The hypothesis that bathorhodopsin is a protonated, ground-state species was based on the observations that all bathorhodopsins studied [101-108] from various species (e.g., chicken, squid, frog) had red-shifted absorption maxima as compared to the parent rhodopsin, and all were stable indefinitely at liquid nitrogen temperature. 

In an attempt to ascertain that bathorhodopsin is the earliest intermediate, the bleaching of cattle rhodopsin was investigated at liquid helium temperature (4 K). Irradiation at wavelengths longer than 530 nm gave a photostationary state contain- 

Low temperature experiments have shown the formation of hypso intermediates from several species [99,103,105-107]. The study of early photoconversion processes in squid [108], which also involved the evaluation of the relative quantum yields among the four pigments (squid rhodopsin, squid batho-, hypso- and isorhodopsin) showed that hypsorhodopsin is a common intermediate of rhodopsin and isorhodopsin there is no direct conversion between rhodopsin and isorhodopsin bathorhodopsin is not converted directly to hypsorhodopsin and both rhodopsin and isorhodopsin convert more efficiently to bathorhodopsin than to hypsorhodopsin. While a temperature dependence of the relaxation processes from the excited state of rhodopsin, and an assumption that batho could be formed from one of the high vibrational levels of the ground state hypso have been invoked to explain these findings [108], the final clarification of this matter awaits results from subpicosecond laser photolysis experiments at liquid helium temperature. 

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The first study in which a full CASSCE treatment was used for the non-adiabatic dynamics of a polyatomic system was a study on a model of the retinal chromophore [86]. The cis-trans photoisomerization of retinal is the primary event in vision, but despite much study the mechanism for this process is still unclear. The minimal model for retinal is l-cis-CjH NHj, which had been studied in an earlier quantum chemisti7 study [230]. There, it had been established that a conical intersection exists between the Si and So states with the cis-trans defining torsion angle at approximately a = 80° (cis is at 0°). Two... 

The mechanism of action of quats has been widely studied. It is generally agreed that their iateraction with the bacterial cell membrane is the primary event resulting ia antimicrobial activity (16,17). 

Under the primary event symbols, the circle represents a component failure for which a description and failure-on-demand or failure frequency data is provided. 

In addition to excess sodium intake, abnormal renal sodium retention may be the primary event in the development of hypertension, and it includes abnormalities in the pressure-natriuresis mechanism. In hypertensive individuals, this theory proposes a shift in the control mechanism preventing the normalization of blood pressure. The mechanisms behind the resetting of the pressure-natriuresis curve may include afferent arteriolar vasoconstriction, decreased glomerular ultrafiltration, or an increase in tubular sodium reabsorption.4 Other theories supporting abnormal renal sodium retention suggest a congenital reduction in the number of nephrons, enhanced renin secretion from nephrons that are ischemic, or an acquired compensatory mechanism for renal sodium retention.9... 

The primary event in the molecular pathogenesis of SCD involves polymerization of deoxygenated HbS. Since RBCs are packaged with such a high concentration of hemoglobin (32-34 g/dL, 320 to 340 g/L or 19.9-21 mmol/L), it is important... 

Additional insight is possible from Fig. 38b. Here we see that the magnitude of the explained variance accounted for by the second PC has noticeably increased after minute 70. This is consistent because, from process knowledge, it is known that removal of water is the primary event in the first part of the batch cycle, while polymerization dominates in the later part, explaining why the variance profile changes around the 70-minute point. 

The primary event which takes place when high energy radiation, such as gamma radiation, interacts with a polymer molecule involves the ejection of an electron, with formation of the polymer cation radical, as shown in Equation (1) ... 

FUNCTION RUBISCO CATALYSES TWO REACTIONS THE CARBOXYLATION OF D-RIBULOSE 1,5-BISPHOSPHATE, THE PRIMARY EVENT IN PHOTOSYNTHETIC CARBON DIOXIDE FIXATION, AS WELL AS THE OXIDATIVE FRAGMENTATION OF THE PENTOSE SUBSTRATE IN THE PHOTORESPIRATION PROCESS. BOTH REACTIONS OCCUR SIMULTANEOUSLY AND IN COMPETITION AT THE SAME ACTIVE SITE. 

A recent report suggests that inhibition of PC synthesis constitutes one of the primary events by which C2-ceramide triggers apoptosis (Ramos et al, 2000). Treatment of cerebral granule neurons with C2-ceramide resulted in a rapid (within 1 hour) reduction in PC biosynthesis, whereas only 6 h after exposure to the agonists the first significant drop in cell viability was observed. The authors further showed that addition of exogenous PC resulted in a dose-dependent full prevention of neuronal death. This was specific for PC, because addition of other glycerohpids Uke, PE, PS, phosphatidylinositol and phosphatidic acid had no effect on C2-ceramide-induced apoptosis. 

All analytical techniques in the TEM are based on the inelastic scattering of the fast beam electrons by the electrons of the atoms in the material investigated. The primary event in each case is the transfer of energy and momentum from the fast electron to a sample atom, thereby exciting the... 

We examine here possible structural effects that may result from or accompany the generation of the primary photoproducts, and speculate about the consequences of concomitant changes in distances,conformations, relative orientations and charges on the electronic profiles of and interactions between the BChls, BPheos and their radicals. Because the primary events in green plant photosynthesis also involve a series of chlorophyll donors and acceptors ( ), similar trends should therefore prevail for chlorophyll radicals as well. Furthermore, radicals of porphyrins and hydroporphyrins (saturated porphyrins such as chlorins and isobacteriochlorins) have been... 

The evidence to-date shows that vertebrate photoreception is mediated by a closely related group of proteins termed opsins. These are G protein-coupled receptors characterized by their ability to bind a vitamin A based chromophore ( -cis-retinal) via a Schiff base linkage using a lysine residue in the 7th transmembrane a helix (Fig. 1). The primary events of image detection by the rods and cones occurs with the absorption of a photon of light by ll-r/r-retinal and its photoisomerization to the AUtrans state (Bums Baylor 2001, Menon et al 2001). Although photoreception is best understood in retinal rods and cones, photoreception is not confined to these structures. In non-mammalian... 

The primary events are deeply described in the literature [5] and are summarized in Eqs. (la)—(If) for the oxidative pathways in which a substrate Redi is involved ... 

The common shape observed for Tq as a function of the substrate or catalyst concentration depending on the primary events depicted in Eqs. (la)-(lf) is normally reported of saturative type as if the rate would be determined by adsorption properties of the substrate on the catalyst surface according to a Langmuir isotherm ... 

Secondary events. These are the changes that may occur in cells exposed to toxic compounds following the primary events. 

It appears that hydrogen-bonds are potentially fast enough so to allow for bimolecular proton-transfer to occur along relaxed hydrogen-bond links, thus making the preparation of such links, which may involve relatively slow solvent fluctuations, the primary event that establishes the proton transfer coordinate. 

Under moderate energies, the primary event of incident particle interaction with crystals of any nature is very simple it is an elastic pair collision resulting in displacement of atoms (ions) into an interstitial position [1, 7, 10] provided they received energy exceeding a threshold value [11] which is typically 10-20 eV. 

Lorimer, G. H., The carboxylation and oxygenation of ribulose-1,5-bisphosphate The primary events in photosynthesis and photorespiration. Ann. Rev. Plant Physiol. 32 349, 1981. Mechanisms and biochemical significance of the carboxylase and oxygenase reactions. 

The photosensitized electron transfer process involves two successive steps (eq. 5) In the primary event an encounter cage complex of the photoproducts is formed. This can either recombine to yield the original reactants or dissociate into separated photoproducts. The separated photoproducts can then recombine by a diffusional back electron transfer reaction to form the original reactants. We have introduced two conceptional approaches as a means for assisting the separation of the encounter cage complex and for the stabilization... 

A considerable amount is known about details of the primary events in electronic excitation. Electronic excitation cross sections are dependent on the charge and velocity of the incident primary ion. Both of these parameters have been confirmed to be the important variables in the emission of secondary molecular ions under bombardment by ions in the 50-100 MeV regime (1 MeV/u) (5-6). The excitation promotes electrons within atoms and molecules to very high energies resulting in ionization and emission of secondary electrons (up to 50 per incident ion) (7). The excitation of electrons in core... 

The photoinduced chemical transformation that follows the excitation process often activates an enzyme cascade or opens an ion channel. These secondary reactions amplify the primary event of light absorption. In some mechanisms, translocation of electrons (photosynthesis, for example) or of... 

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