Showing papers by "Jagiellonian University published in 1997"
TL;DR: This review discusses various aspects of the interactions between heavy metals and mycorrhizal fungi, including the effects of heavy metals on the occurrence of mycor RH fungi, heavy metal tolerance in these micro-organisms, and their effect on metal uptake and transfer to plants.
Abstract: High concentrations of heavy metals in soil have an adverse effect on micro-organisms and microbial processes. Among soil microorganisms, mycorrhizal fungi are the only ones providing a direct link between soil and roots, and can therefore be of great importance in heavy metal availability and toxicity to plants. This review discusses various aspects of the interactions between heavy metals and mycorrhizal fungi, including the effects of heavy metals on the occurrence of mycorrhizal fungi, heavy metal tolerance in these micro-organisms, and their effect on metal uptake and transfer to plants. Mechanisms involved in metal tolerance, uptake and accumulation by mycorrhizal hyphae and by endo- or ectomycorrhizae are covered. The possible use of mycorrhizal fungi as bioremediation agents in polluted soils or as bioindicators of pollution is also discussed.
786 citations
TL;DR: In this paper, the authors present four X-ray/gamma-ray spectra of Cyg X-1 observed in the hard ('low') state simultaneously by Ginga and GRO/OSSE on 1991 July 6.
Abstract: We present four X-ray/gamma-ray spectra of Cyg X-1 observed in the hard ('low') state simultaneously by Ginga and GRO/OSSE on 1991 July 6. The 3-30 keV Ginga spectra are well represented by power laws with an energy spectral index of alpha~0.6 and a Compton reflection component including a fluorescent Fe K-alpha corresponding to the solid angle of the reflector of ~0.3 times 2 Pi. The overall Ginga/OSSE spectra can be modelled by repeated Compton scattering in a mildly-relativistic, tau ~1, plasma. However, the high-energy cutoff is steeper than that due to single-temperature thermal Comptonisation. It can be described by a superposition of dominant optically-thin, thermal emission at kT~140 keV and a Wien-like component from an optically-thick plasma at kT~50 keV. The X-ray spectra do not show the presence of an anisotropy break required if thermal Compton scattering takes place in a corona above a cold disc. Also, the flat spectral index shows that the plasma is soft-photon starved, i.e., the luminosity in incident soft X-ray seed photons is very much less than that in the hard X-rays. Furthermore, the observed solid angle of the reflector is significantly less than 2 pi. These facts taken together strongly rule out a disc-corona geometry. Rather, the observed spectra are consistent with a geometry in which the cold accretion disc (which both supplies the seed soft X-rays and reflects hard X-rays) only exists at large radii, while the Comptonising hot plasma is located in an inner region with no cold disc. This hot plasma consists of either pure electron-positron pairs if the source size is ~5 Schwarzschild radii or it contains also protons if the size is larger.
282 citations
TL;DR: In this article, the Kohn-Sham (KS) density functional theory (DFT) is used to calculate the global valence, which is a generalized distance measure measuring a degree of similarity between the two charge-and-bond-order (CBO) matrices.
Abstract: The recent Hartree-Fock (HF) difference approach to the chemical valence indices (ionic and covalent), formulated in the framework of the pair-density matrix, is implemented within the Kohn-Sham (KS) density functional theory (DFT). The valence numbers are quadratic in terms of displacements of the molecular spin-resolved charge-and-bond-order (CBO) matrix elements, relative to values in the separated atoms limit (SAL). It is shown that the global valence represents a generalized “distance” quantity measuring a degree of similarity between the two CBO matrices: the molecular and SAL. Numerical values for typical molecules exhibiting single and multiple bonds demonstrate that the KS orbitals give rise to these new bond valences in good agreement with both chemical and HF predictions. This KS bond multiplicity analysis is applied to the chemisorption system including the allyl radical and a model surface cluster of molybdenum oxide. It is concluded that the quadratic valence analysis represents a valuable procedure for extracting useful chemical information from standard DFT calculations. © 1997 John Wiley & Sons, Inc.
247 citations
TL;DR: The elucidation of the kinetics of inhibition by the range of compounds and the development of the titration method for gingipains will considerably aid in future studies on the proteases elaborated by P. gingivalis.
Abstract: Porphyromonas gingivalis is one of the major pathogens associated with periodontal disease and releases powerful cysteine proteinases known as the gingipains, which are key virulence factors for this organism. The three forms of gingipains, gingipain R1, gingipain R2 (gingipain Rs) and gingipain K, which cleave specifically after arginine (R) or lysine (K) residues, were characterized in terms of the kinetics of their interaction with a wide range of synthetic peptidyl chloromethane inhibitors and a peptidyl (acyloxy)methane. Chloromethane inhibitors were found to inhibit all the enzymes to varying degree dependent on the peptidyl components of the inhibitor. Thus, inhibitors containing a basic residue at P1 rapidly inactivated the gingipains and some specificity could be seen at the P2 site. The (acyloxy)methane inhibitor, Cbz-Phe-Lys-CH2OCO-2,4,6-Me3-Ph, was very specific in its rapid inhibition of gingipain K over the gingipains R. This inhibitor, together with the peptidyl chloromethanes, D-Phe-Pro-Arg-CH2Cl and D-Phe-Phe-Arg-CH2Cl, which reacted most rapidly with the Arg-specific proteinases, could be used to active site titrate purified forms of the enzymes and enzymes found in crude fractions such as intact P. gingivalis cells, vesicles or membrane fractions. From these titrations it was evident that gingipains R were always in an excess of about 3-fold over gingipain K and that the gingipains as a whole made up 85% of the proteolytic activity associated with the bacterium. The elucidation of the kinetics of inhibition by the range of compounds and the development of the titration method for gingipains will considerably aid in future studies on the proteases elaborated by P. gingivalis.
176 citations
TL;DR: Examination of the properties of each proteinase clearly indicates a role(s) for both in the dysregulation of a number of normally tightly controlled pathways, and it seems likely that both P. gingivalis-derived proteinases are important virulence factors in the development of periodontal disease.
Abstract: Porphyromonas gingivalis contains exceedingly high concentrations of cysteine proteinases with trypsin-like activity which have been implicated as virulence factors in adult-onset periodontitis. These enzymes, referred to as gingipains, cleave protein and peptide substrates after arginine (gingipain R) and lysine residues (gingipain K), and it has been found that neither is easily inhibited by host proteinase inhibitors. Examination of the properties of each proteinase clearly indicates a role(s) for both in the dysregulation of a number of normally tightly controlled pathways. The effects of such uncontrolled proteolysis are the development of edema (kallikrein/kinin pathway activation by gingipain R), neutrophil infiltration (complement pathway activation by gingipain R), and bleeding (degradation of fibrinogen by gingipain K). Since three of the major hallmarks of periodontitis involve increased crevicular flow, neutrophil accumulation at infected sites and bleeding on probing, it seems likely that both P. gingivalis-derived proteinases are important virulence factors in the development of periodontal disease.
175 citations
TL;DR: The arbuscular mycorrhizal status of two plant communities on a calamine spoil mound in southern Poland was surveyed: an undisturbed grassland community and an early succession community that developed after complete removal of the surface layer of the calamine substrate about 10 years earlier.
Abstract: The arbuscular mycorrhizal (AM) status of two plant communities on a calamine spoil mound (rich in cadmium, lead and zinc) in southern Poland was surveyed: an undisturbed grassland community and an early succession community that developed after complete removal of the surface layer of the calamine substrate about 10 years earlier. The undisturbed site harbored 40 herbaceous species making up 87% of the absolute cover. AM colonization was recorded in 25 species accounting for 77% of the relative cover. Species with 51–75% AM root colonization such as Festuca ovina and Leontodon hispidus dominated the undisturbed turf, contributing 45% to the relative cover. Carex ssp. were the most abundant nonmycorrhizal plants and accounted for 9% of the relative cover. Spores of Glomus aggregatum, G. constrictum, G. fasciculatum, G. pansihalos, Glomus sp. and Entrophospora sp. averaged 25 per 100 g dry substrate at the undisturbed site. The disturbed site was colonized by 25 species accounting for 17% of the absolute cover. Among the AM plants, most abundant were the species with up to 20% AM root colonization, such as Agrostis stolonifera and Thymus pulegioides, wich accounted for 24% of the relative cover. Nonmycorrhizal species, such as Biscutella laevigata,Cardaminopsis arenosa, Gypsophila fastigiata and Silene vulgaris, dominated the early succession community and contributed 64% to the relative cover. Spores of G. fasciculatum and Entrophospora sp. averaged 20 per 100 g dry substrate at the disturbed site.
162 citations
TL;DR: In this paper, the authors studied the effect of the beam energies of the nucleon-nucleon collisions on the kaon production in the nuclear medium and found that the ratio of k = 0.8-1.8 GeV/nucleus with the GSI spectrometer at GSI.
Abstract: Kaon production has been studied in $\mathrm{Ni}+\mathrm{Ni}$ collisions at beam energies of 0.8--1.8 GeV/nucleon with the kaon spectrometer at GSI. The ${K}^{+}$ production cross section increases as ${E}_{\mathrm{beam}}^{5.3\ifmmode\pm\else\textpm\fi{}0.2}$. Both ${K}^{+}$ and ${K}^{\ensuremath{-}}$ mesons are predominantly produced in central collisions. The ${K}^{\ensuremath{-}}/{K}^{+}$ ratio measured at equivalent beam energies below the respective particle production threshold is considerably larger for $\mathrm{Ni}+\mathrm{Ni}$ collisions than for nucleon-nucleon collisions near threshold. This is evidence for an enhanced ${K}^{\ensuremath{-}}$ production in the nuclear medium.
158 citations
TL;DR: A dynamic programming model which optimizes resource allocation to growth, reproduction and somatic repair is reported, resulting in delayed ageing and low growth rates, delayed maturity, large body size and dramatic enhancement of survival and maximum lifespan.
Abstract: Models of life history evolution predict optimal traits of a simplified organism under various environmental conditions, but they at most acknowledge the existence of ageing. On the other hand, genetic models of ageing do not consider the effects of ageing on life histroy traits other than fecundity and longevity. This paper reports the results of a dynamic programming model which optimizes resource allocation to growth, reproduction and somatic repair. A low extrinsic (environmentally caused) mortality rate and high repair efficiency promote allocation to repair, especially early in life, resulting in delayed ageing and low growth rates, delayed maturity, large body size and dramatic enhancement of survival and maximum lifespan. The results are generally consistent with field, comprative and experimental data. They also suggest that the relationships between maximum lifespan and age at maturity and body size observed in nature may be by–products of optimal allocation strategies.
134 citations
TL;DR: It is shown that lung-derived epithelial cells not only have the capacity to synthesize functional α1-PI but also to increase the rate of its production when stimulated by specific inflammatory mediators, including oncostatin M, interleukin-1, and the glucocorticoid analogue, dexamethasone.
130 citations
TL;DR: The role of melatonin and L‐tryptophan in prevention of acute gastric lesions induced by stress, ethanol, ischemia, and aspirin is studied.
Abstract: Melatonin, a pineal hormone, synthesized from L-tryptophan, is known to exist in the gut and to scavenge oxygen free radicals but its role in gastroprotection against acute lesions induced by various strong irritants has been little studied. In this study, we determined the effects of melatonin and L-tryptophan on gastric secretion and the formation of acute gastric lesions induced by absolute ethanol, acidified aspirin (ASA), stress, and ischemia-reperfusion (I/R). Area of gastric lesions was determined by planimetry, gastric blood flow (GBF) was measured using a H2-gas clearance technique, and blood was withdrawn for the measurement of free radicals, plasma gastrin, and melatonin concentration by specific radioimmunoassay. Intragastric (i.g.) administration of melatonin (2.5-10 mg/kg) or L-tryptophan (25-200 mg/kg) failed to affect gastric lesions by ethanol and ASA but dose-dependently reduced the lesions provoked by stress and I/R; this protective effect was accompanied by a significant rise in plasma melatonin level, GBF, and DNA synthesis and by a marked fall in blood free radicals. L-tryptophan, which significantly elevated the plasma melatonin by about 3-5-fold, also reduced the stress and I/R-induced lesions and blood levels of free radicals, while increasing the GBF, DNA synthesis, and plasma gastrin levels. Inhibition of mucosal generation of PGE2 by indomethacin abolished the protection and the rise of GBF afforded by melatonin and L-tryptophan, whereas pretreatment with N(G)-nitro-L-arginine (L-NNA), to suppress nitric oxide (NO) synthase, was without any effect. We conclude that melatonin applied exogenously in pharmacological doses and that released by the administration of its precursor, L-tryptophan, protect gastric mucosa from the damage induced by stress and I/R possibly by a mechanism involving the scavenging of free radicals and gastric hyperemia probably mediated by endogenous prostaglandin but not NO.
126 citations
TL;DR: For horseshoe-type mappings which are geometrically similar to Smale's horseshoes, the existence of chaotic dynamics - the semi-conjugacy to the shift on a finite number of symbols is proved by means of the fixed point index.
Abstract: We introduce horseshoe-type mappings which are geometrically similar to Smale's horseshoes. For such mappings we prove by means of the fixed point index the existence of chaotic dynamics - the semi-conjugacy to the shift on a finite number of symbols. Our theorem does not require any assumptions concerning derivatives, it is a purely topological result. The assumptions of our theorem are then rigorously verified by computer assisted computations for the classical Henon map and for classical Rossler equations.
TL;DR: Pavloff et al. as discussed by the authors showed that the lysine-specific gingipain (gingipain K; KGP) is also biosynthesized as a polyprotein precursor that is 22% homologous to the proteinase domain of RGP-1 and multiple adhesin domains This precursor is similarly processed at distinct sites to yield active KGP.
TL;DR: This data indicates that aspirin sensitivity in individuals with adult‐onset asthma is more likely to be due to immune mechanisms than to interference with biochemical pathways.
Abstract: Background Aspirin-induced asthma (AIA) affects one in 10 individuals with adult-onset asthma. It is not known if aspirin sensitivity is due to immune mechanisms or to interference with biochemical pathways. Objective The study aimed to test for possible involvement of the genes of the Major Histocompatibility Complex (MHC) in AIA. Methods HLA-DPB1 and HLA-DRB1 genotyping was carried out by DNA methods in 59 patients with positive challenge tests for AIA and in 48 normal and 57 asthmatic controls. Results The DPB1*0301 frequency was increased in AIA patients when compared with normal controls (19.5% vs 5.2%, Odds Ratio = 4.4, 95% Confidence Interval (CI) 1.6-12.1, P = 0.002), and compared with asthmatic controls (4.4%, OR = 5.3, 95% CI = 1.9-14.4, P = 0.0001). The frequency of DPB1*0401 in AIA subjects was decreased when compared with normal controls (28.8% vs 49.0%, OR = 0.42, 95% CI = 0.24-0.74, P = 0.003) and asthmatic controls (45.6%, OR = 0.48, 95% CI = 0.28-0.83, P = 0.008). The results remained significant when corrected for multiple comparisons. There were no significant HLA-DRB1 associations with AIA. Conclusion The presence of an HLA association suggests that immune recognition of an unknown antigen may be part of the aetiology of AIA.
TL;DR: Hsp70 were found in all animals tested, including controls, and their levels were not clearly related to the laboratory treatment with chemicals or temperature or to the degree of contamination in polluted areas, in centipedes from unpolluted areas.
TL;DR: The results of this study indicate that the spectra at g = 4.3, attributable to Fe3+, provides a useful parameter for determining the amount of paramagnetic iron bound to melanin, and this data together with the magnitude of the free radical signal from melanin provides an indication of the number ofIron bound to neuromelanin in intact human substantia nigra.
TL;DR: In this paper, six precipitates of calcium phosphates with Ca P molar ratios in the range of 1.502-1.717 have been prepared by the wet method.
TL;DR: Adverse reactions to aspirin and other nonsteroidal anti-inflammatory drugs (NSAID) may have various clinical presentations and different pathogeneses (2-4).
Abstract: Shortly after its introduction into therapy, aspirin was implicated as the cause of a violent bronchospasm. Tlie association of aspirin sensitivity, asthma, and nasal polyps was described by F. Widal and eolleagues in 1922. Tliis clinical entity, subsequently named the aspirin triad, was brought to physicians' attention by Samter & Beers (1), who, in the late 1960s, presented a perceptive description of the elinical course of the syndrome. Adverse reactions to aspirin and other nonsteroidal anti-inflammatory drugs (NSAID) may have various clinical presentations and different pathogeneses (2-4). Here we discuss one of these presentations. It affects asthmatics and indeed constitutes a special type of asthma called aspirinindueed asthma (AIA).
TL;DR: A survey of the work on the catalytic oxidation of benzene to maleic anhydride over vanadia-molybdena catalysts can be found in this article, which includes the phase composition of the catalyst and its transformations under the influence of the changes in redox potential of the gas phase in catalytic reactor, kinetics of the process as well as its molecular mechanism.
Abstract: The paper presents the survey of the work on the catalytic oxidation of benzene to maleic anhydride over vanadia-molybdena catalysts. It includes the studies on the phase composition of the catalyst and its transformations under the influence of the changes in redox potential of the gas phase in catalytic reactor, kinetics of the process as well as its molecular mechanism.
TL;DR: Evidence is found that children exposed to ETS in their homes were more susceptible to acute respiratory tract illnesses than unexposed children, and a dose-response relationship between degree of exposure supports a causal explanation for the association observed.
Abstract: This study compared susceptibility to respiratory morbidity in a cohort of 9-year-old children exposed congenitally and postnatally to environmental tobacco smoke (ETS) to susceptibility in a cohort of unexposed children. The epidemiologic study included 1129 children: 594 boys and 535 girls attending the second grade of grammar schools in Krakow, Poland. We found strong evidence that children exposed to ETS in their homes were more susceptible to acute respiratory tract illnesses than unexposed children. A dose-response relationship between degree of exposure [for lower ETS exposure, odds ratio (OR) = 1.32; for higher ETS exposure, OR = 1.74] supports a causal explanation for the association observed. The significant trend of increased risk of respiratory infections due to ETS level in nonatopic children whose mothers did not smoke cigarettes during pregnancy suggests a direct effect of ETS exposure on the child's respiratory health. ETS combined with allergy nearly tripled the risk of acute respiratory tract illness (OR = 3.39; 95% CI, 1.93-5.93), and maternal smoking during pregnancy had a modifying effect on the risk of respiratory illnesses due to ETS after accounting for atopy. The stronger effect of ETS in atopic children and in those whose mothers smoked during pregnancy may be result of biologic interaction of endogenous and environmental factors. The results of this study are of relevance to public health policy, as children with higher risk of respiratory infections may be more susceptible to environmental hazards later in adolescence or in adulthood. Respiratory infections also increase demands for medical interventions in terms of outpatient services and hospital administrations. In addition, respiratory illnesses cause missed school days, and caring for a sick child may lead to absenteeism from work.
TL;DR: In this article, a method of detection of chaos in dynamical systems generated by time-periodic nonautonomous differential equations is presented, based on the existence of some sets (called periodic isolating segments) in the extended phase space, satisfying some topological conditions.
TL;DR: Melatonin and L-tryptophan protect the gastric mucosa from damage by stress and ischaemia reperfusion, and this action is mediated, at least in part, by the limitation in the free radicals, the stimulation of mucosal generation of PG and by the increase in gastric blood flow.
Abstract: Background: Melatonin, a pineal hormone that is biosynthesized from L-tryptophan, is known to scavenge oxygen free radicals and to be present in the gut, but little is known about the role of this hormone and its precursor, L-tryptophan, in protecting the gastric mucosa from damage accompanied by increase in the generation of oxygen radicals. Methods: This study was designed to determine the effects of melatonin and L-tryptophan on the formation of acute gastric lesions induced by stress and ischaemia reperfusion and, for comparison, by topical irritants such as 100% ethanol or acidified acetylsalicylic acid. Results: It was found that pretreatment with melatonin in doses ranging from 1.2 to lOmg/kg dose-dependently reduced the stress-induced gastric lesions and was accompanied by a reduction in blood-free radicals and by attenuation of the fall in gastric blood flow. L-tryptophan applied intragastrically in doses ranging from 1 to lOOmg/kg also reduced dose-dependently the lesions induced by stress; this...
TL;DR: It is concluded that melatonin is capable of protecting gastric mucosa from the damage caused by ischemia-reperfusion and that this action is mediated, at least in part, by limitation of the generation of free radicals and by attenuation of the fall in gastric blood flow.
TL;DR: It is concluded that intranasal FP is an effective therapy for chronic eosinophilic rhinitis in patients with AIA.
Abstract: We performed a double-blind, crossover, placebo-controlled study on the effect of fluticasone propionate (FP) treatment on chronic eosinophilic rhinosinusitis in 15 patients with aspirin-induced asthma (AIA). There were 10 women and five men aged 32-60 years; average: 45 years. After a 10-day run-in period, patients underwent two 4-week treatment courses (FP vs placebo), separated by a 2-week washout interval. Clinical activity of FP was evaluated by daily measurement of peak nasal inspiratory flow (PNIF) and a scoring system of subjective symptoms. Nasal challenges with E-lysine aspirin, using active anterior rhinomanometry, were performed at the entry and on the last day of each treatment period. Weekly mean values of symptom scores were generally lower and PNIF measurements higher during treatment with FP than with placebo. This difference was statistically significant for most recorded parameters for the whole 4-week FP treatment. On average, the reactions evoked by aspirin nasal challenge were significantly shorter and milder after treatment with FP than with placebo. In 8/13 patients, FP completely prevented aspirin-precipitated nasal reaction, whereas protection after placebo was observed in only 2/12 subjects (P = 0.004). We conclude that intranasal FP is an effective therapy for chronic eosinophilic rhinitis in patients with AIA.
TL;DR: In this article, the authors compared the antioxidant activity of several prenyllipids, such as plastoquinol-9, α-tocopherol quinol (α-TQH2), ubiquinol-10 (UQH-2-10), α-T, and α-COPEL quinols, in terms of the second order rate constants in Tris buffer (pH=6.5).
TL;DR: In a two-choice test, naive females were more attracted to dominant males than to subordinates as manifested by the females' higher level of activity, more sniffs, and more time spent sniffing males of high rank.
TL;DR: The protective activity of l-arginine involves gastric hyperemia mediated by NO and a mild irritant effect due to enhanced generation of endogenous PG, and the ulcer healing properties ofl-arg inine depend upon its hyperemic and angiogenic actions, possibly involving NO.
Abstract: Nitric oxide (NO) synthesized from L-arginine interacts with prostaglandins (PG) and sensory neuropeptides in the regulation of mucosal integrity, but the role of L-arginine, a substrate for NO-synthase, in gastroprotection and healing of chronic gastric ulcers has been little studied. In this study we compared the effects of intragastric (i.g.) and systemic (i.v.) administration of L-arginine or D-arginine on gastric secretion and acute gastric lesions provoked in rats by i.g. application of 100% ethanol, acidified aspirin (ASA), or the exposure to 3.5h of water immersion and restraint stress (WRS). In addition, the effects of L-arginine on ulcer healing and the formation of new vessels (angiogenesis) were determined, using monoclonal antibody (MAb E-9). L-arginine (10-200 mg/kg i.g.) failed to significantly affect gastric secretion but dose-dependently reduced the gastric lesions induced by 100% ethanol. ASA, and WRS, the doses inhibiting 50% of these lesions being 65, 94, and 72 mg/kg, respectively. This protection was accompanied by a significant rise in the gastric blood flow (GBF), whereas L-arginine given i.v. failed to affect the ethanol-lesions and the GBF. D-arginine or the NO-related amino acids--L-glutamine, L-citrulline, or L-ornithine--failed to significantly influence these lesions. Suppression of the generation of mucosal PG by indomethacin or capsaicin-denervation attenuated the protection and hyperemia induced by L-arginine. The inhibition of constitutive NO synthase by L-NNA had no significant effect on the protection afforded by L-arginine, but reduced the gastric hyperemia accompanying this protection. L-arginine (150 mg/kg per day, i.g.) accelerated the ulcer healing and increased GBF at the ulcer margin, and angiogenesis, whereas treatment with L-NNA had an opposite effect. L-arginine added to NG-nitro-L-arginine (L-NNA) restored the ulcer healing, hyperemia, and angiogenesis. We conclude that: (1) the protective activity of L-arginine involves gastric hyperemia mediated by NO and a mild irritant effect due to enhanced generation of endogenous PG, and (2) the ulcer healing properties of L-arginine depend upon its hyperemic and angiogenic actions, possibly involving NO.
TL;DR: The data indicate that photoinduced melanin radicals oxidize ascorbate via one-electron transfer reaction, and it can be concluded that melanin acts as an electron transfer agent in the absence of oxygen.
Abstract: To determine the role of major chromophores of the human retinal pigment epithelium (RPE) in photooxidation of ascorbate, we monitored spectrophotometrically rates of ascorbate depletion, induced by blue light, in suspensions of human RPE melanin, melanolipofuscin and lipofuscin and in preparation of pigmented and nonpigmented bovine RPE cells. The results clearly show that melanin is the key retinal pigment responsible for the photosensitized oxidation of exogenous ascorbate. To elucidate the mechanism of the photooxidation process, we used purified RPE melanin granules and synthetic dopa (dihydroxyphenylalanine) melanin and employed electron spin resonance (ESR) spectroscopy, ESR oximetry and oxidase electrode. Our data indicate that photoinduced melanin radicals oxidize ascorbate via one-electron transfer reaction. The reduced melanin is reoxidized by molecular oxygen with the formation of superoxide anion and hydrogen peroxide, while the ascorbate radicals decay by disproportionation. Because in the absence of oxygen, no measurable oxidation of ascorbate is observed, it can be concluded that melanin acts as an electron transfer agent. Biological implications of this study remain unclear; however, the formation of oxygen-reactive species that accompany melanin-mediated photooxidation of ascorbate may represent a potential risk to the RPE that should be minimized by yet unknown cellular mechanisms.
TL;DR: The results support the proposal that antithrombin circulates in a constrained conformation, which when released, in this study by perturbation of the bonding of P1 Arg to the body of the molecule, allows the reactive site loop to take up the active inhibitory conformation with exposure of the P1Arg.
TL;DR: Social stress, which is a part of the interaction between animals, can be defined as the set of physical stresses caused specifically by the presence and actions of certain conspecifics.
TL;DR: In this article, the electronic properties of bridging surface oxygens are investigated and the ionic character of the substrate is confirmed by the atom populations while bond order results show additional covalent binding in agreement with chemical intuition.