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51.
The terminal electron acceptor of Photosystem II, PSII, is a linear complex consisting of a primary quinone, a non-heme iron(II), and a secondary quinone, Q(A)Fe(2+)Q(B). The complex is a sensitive site of PSII, where electron transfer is modulated by environmental factors and notably by bicarbonate. Earlier studies showed that NO and other small molecules (CN(-), F(-), carboxylate anions) bind reversibly on the non-heme iron in competition with bicarbonate. In the present study, we report on an unusual new mode of transient binding of NO, which is favored in the light-reduced state (Q(A)(-)Fe(2+)Q(B)) of the complex. The related observations are summarized as follows: (i) Incubation with NO at -30 degrees C, following light-induced charge separation, results in the evolution of a new EPR signal at g = 2.016. The signal correlates with the reduced state Q(A)(-)Fe(2+) of the iron-quinone complex. (ii) Cyanide, at low concentrations, converts the signal to a more rhombic form with g values at 2.027 (peak) and 1.976 (valley), while at high concentrations it inhibits formation of the signals. (iii) Electron spin-echo envelope modulation (ESEEM) experiments show the existence of two protein (14)N nuclei coupled to electron spin. These two nitrogens have been detected consistently in the environment of the semiquinone Q(A)(-) in a number of PSII preparations. (iv) NO does not directly contribute to the signals, as indicated by the absence of a detectable isotopic effect ((15)NO vs (14)NO) in cw EPR. (v) A third signal with g values (2.05, 2.03, 2.01) identical to those of an Fe(NO)(2)(imidazole) synthetic complex develops slowly in the dark, or faster following illumination. (vi) In comparison with the untreated Q(A)(-)Fe(2+) complex, the present signals not only are confined to a narrow spectral region but also saturate at low microwave power. At 11 K the g = 2.016 signal saturates with a P(1/2) of 110 microW and the g = 2.027/1.976 signal with a P(1/2) of 10 microW. (vii) The spectral shape and spin concentration of these signals is successfully reproduced, assuming a weak magnetic interaction (J values in the range 0.025-0.05 cm(-)(1)) between an iron-NO complex with total spin of (1)/(2) and the spin, (1)/(2), of the semiquinone, Q(A)(-). The different modes of binding of NO to the non-heme iron are examined in the context of a molecular model. An important aspect of the model is a trans influence of Q(A) reduction on the bicarbonate ligation to the iron, transmitted via H-bonding of Q(A) with an imidazole ligand to the iron. 相似文献
52.
The solution of the shortest path problem in biochemical systems constitutes an important step for studies of their evolution. In this paper, a linear programming (LP) algorithm for calculating minimal pathway distances in metabolic networks is studied. Minimal pathway distances are identified as the smallest number of metabolic steps separating two enzymes in metabolic pathways. The algorithm deals effectively with circularity and reaction directionality. The applicability of the algorithm is illustrated by calculating the minimal pathway distances for Escherichia coli small molecule metabolism enzymes, and then considering their correlations with genome distance (distance separating two genes on a chromosome) and enzyme function (as characterised by enzyme commission number). The results illustrate the effectiveness of the LP model. In addition, the data confirm that propinquity of genes on the genome implies similarity in function (as determined by co-involvement in the same region of the metabolic network), but suggest that no correlation exists between pathway distance and enzyme function. These findings offer insight into the probable mechanism of pathway evolution. 相似文献
53.
Missirlis F Rahlfs S Dimopoulos N Bauer H Becker K Hilliker A Phillips JP Jäckle H 《Biological chemistry》2003,384(3):463-472
Cellular defense systems against reactive oxygen species (ROS) include thioredoxin reductase (TrxR) and glutathione reductase (GR). They generate sulfhydryl-reducing systems which are coupled to antioxidant enzymes, the thioredoxin and glutathione peroxidases (TPx and GPx). The fruit fly Drosophila lacks a functional GR, suggesting that the thioredoxin system is the major source for recycling glutathione. Whole genome in silico analysis identified two non-selenium containing putative GPx genes. We examined the biochemical characteristics of one of these gene products and found that it lacks GPx activity and functions as a TPx. Transgene-dependent overexpression of the newly identified Glutathione peroxidase homolog with thioredoxin peroxidase activity (Gtpx-1) gene increases resistance to experimentally induced oxidative stress, but does not compensate for the loss of catalase, an enzyme which, like GTPx-1, functions to eliminate hydrogen peroxide. The results suggest that GTPx-1 is part of the Drosophila Trx antioxidant defense system but acts in a genetically distinct pathway or in a different cellular compartment than catalase. 相似文献
54.
55.
The interaction of the anticancer antibiotic altromycin B and its isostructrural Pt(II) and Pd(II) metal complexes with native calf thymus (CT) DNA was studied using UV-thermal denaturation experiments, circular dichroism spectroscopy and temperature controlled spectrophotometric titrations. Altromycin B stabilizes the double helix by raising the T(m), mainly by intercalation of its chromophore between the base pairs and interacting electrostatically via its sugar moieties with the edges of the DNA helix. Moreover, altromycin B induces a B-->A structural transition of CT DNA. The effect on DNA stability and conformation depends on the metal ion. Pt(II) and Pd(II) complexes induce the B-->A structural transition and stabilize the double helix similarly but they present lower final hyperchromicity due to premelting effects which were caused by intra- and interstrand crosslinking. Thus, a synergic effect of the metal ions to altromycin B-CT DNA interaction is observed in both cases. Altromycin B interacts with 5'-GMP, 5'-AMP and 5'-CMP by electrophilic attack of the opened epoxide ring to the N(7)G, N(1)/N(7)A and N(3)C. Thus, covalent binding between these nucleotides and altromycin B takes place and explain the multiple binding mode suggested by the studies of the interaction of altromycin B and its complexes with DNA. The [Pd(II)-altroB] complex dissociates in the presence of the nucleotides, and various species of Pd(II)-nucleotide complexes, especially with 5'-GMP, are formed. The [Pt(II)-altroB] complex dissociates too, but only one or two species of Pt(II)-nucleotide complexes are formed, and in the case of 5'-AMP interaction the formation of a tertiary altroB-Pt(II)-5'AMP complex is proposed. 5'-TMP reacts very weakly in comparison with the other three nucleotides. These interactions were followed by 1H-NMR. 相似文献
56.
Intrafamilial spread of Helicobacter pylori: a genetic analysis 总被引:4,自引:0,他引:4
Roma-Giannikou E Karameris A Balatsos B Panayiotou J Manika Z Van-Vliet C Rokkas T Skandalis N Kattamis C 《Helicobacter》2003,8(1):15-20
Background. A high incidence of Helicobacter pylori among family members of children with H. pylori gastritis has previously been documented on biopsy material. The main objective of this study was the genetic clarification of H. pylori strains involved in intrafamilial dispersion. Materials and Methods. Formalin‐fixed, paraffin‐embedded material of antral mucosa from 32 members of 11 families was studied for the presence of genetic homogeneity. To achieve this goal, the entire genome of H. pylori was studied by the polymerase chain reaction (PCR)‐based random amplified polymorphic DNA (RAPD) fingerprinting method. Furthermore, the Urease A gene was analyzed using a multiplex PCR‐assay and an alternative mutation detection method based on the Hydrolink? analysis. Results. RAPD fingerprinting confirmed that closely related H. pylori strains were involved in the intrafamilial dispersion. Mutations and small deletions in Urease A gene were found in 22 out of 32 individuals. Conclusions. The homology of the H. pylori genome in members of the same family strongly supports the hypothesis of transmission of H. pylori from person‐to‐person or from a common source. 相似文献
57.
The chemical compositions of hexane extracts of the lipid fraction of the roots of the medicinal Boraginaceous species Alkanna tinctoria, Onosma heterophylla, Macrotomia densiflora and Onosma hispidium are presented and their phytochemical relevance evaluated. The predominating fatty acids in all of the root lipids were stearic, palmitic, oleic, linoleic and gamma-linolenic acids, while the latter and stearidonic acid predominated in the seeds and leaves of various Boraginaceous species. The indigenous presence of methyl, ethyl and isopropyl esters of fatty acids, reported for the first time in the roots of higher plants, is considered to be of particular importance in the biosynthesis of fatty substances. The results suggest the use of fatty acids as chemotaxonomic markers for Boraginaceous species and the utilisation of Boraginaceous species as new commercial sources for fatty acids with valuable medicinal and nutritional properties. 相似文献
58.
Frangogiannis NG Mendoza LH Smith CW Michael LH Entman ML 《Cell and tissue research》2000,302(3):365-376
Endotoxemia is associated with a systemic inflammatory response leading to organ-specific leukocyte recruitment and tissue injury. Chemokine expression has been demonstrated in various models of sepsis and may mediate tissue infiltration with inflammatory cells. In this study we examined expression of the C-X-C chemokine interferon-gamma-inducible protein-10 (IP-10), a potent T-lymphocyte chemoattractant, in a canine model of endotoxemia and investigated mechanisms of cytokine-mediated IP-10 induction in endothelial cells. Control canine tissues showed negligible expression of IP-10 message, with the exception of the spleen. Endotoxemic dogs demonstrated a robust induction of IP-10 mRNA in the heart, lung, kidney, liver, and spleen. Immunohistochemical studies indicated that IP-10 was predominantly localized in cardiac venular endothelial cells, bronchial epithelial cells, renal mesangial cells, and in the splenic red pulp of endotoxemic dogs. In addition, IP-10 expression was associated with T-lymphocyte infiltration in canine tissues. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) induced a marked upregulation of IP-10 message in canine venular endothelial cells. IP-10 expression in TNF-alpha-stimulated endothelial cells peaked at 6 h of stimulation and returned to baseline levels after 24 h. In addition, macrophage colony-stimulating factor (M-CSF) induced a dose-dependent induction of IP-10 mRNA in canine endothelial cells. M-CSF-mediated IP-10 expression peaked after 6 h of incubation and returned to baseline levels after 24 h. Canine endotoxemia is associated with a robust early expression of IP-10 in multiple tissues. IP-10 induction may be important in regulating lymphocyte recruitment and function. TNF-alpha, IL-1 beta, and M-CSF are potent inducers of IP-10 in canine endothelial cells and may indirectly mediate lymphocyte chemotaxis and activation in inflammatory processes. 相似文献
59.
Tsoukias Nikolaos M.; Tannous Ziad; Wilson Archie F.; George Steven C. 《Journal of applied physiology》1998,85(2):642-652
Endogenousproduction of nitric oxide (NO) in the human lungs has many importantpathophysiological roles and can be detected in the exhaled breath. Anunderstanding of the factors that dictate the shape of the NOexhalation profile is fundamental to our understanding of normal anddiseased lung function. We collected single-exhalation profiles of NOand CO2 from normal human subjectsafter inhalation of ambient air (~15 parts/billion) and examined theeffect of a 15-s breath hold and exhalation flow rate(E) on thefollowing features of the NO profile:1) series dead space,2) average concentration in phaseIII with respect to time and volume,3) normalized slope of phase IIIwith respect to time and volume, and4) elimination rate at endexhalation. The dead space is ~50% smaller for NO than forCO2 and is substantially reducedafter a breath hold. The concentration of exhaled NO is inverselyrelated to E,but the average NO concentration with respect to time has a stronger inverse relationship than that with respect to volume. The normalized slope of phase III NO with respect to time and that with respect tovolume are negative at a constantE but can bemade to change signs if the flow rate continuously decreases during theexhalation. In addition, NO elimination at end exhalation vs.E produces anonzero intercept and slope that are subject dependent and can be usedto quantitate the relative contribution of the airways and the alveolito exhaled NO. We conclude that exhaled NO has an airway and analveolar source. 相似文献
60.
Anastasia E. Konstantinidou Georgios Agrogiannis Stavros Sifakis Apostolos Karantanas Vassileios Harakoglou Petros Kaminopetros Angeliki Hatzaki Michael B. Petersen Charalampos Karadimas Voula Velissariou Stylianos Velonis Nikolaos Papantoniou Aristeidis Antsaklis Efstratios Patsouris 《Birth defects research. Part A, Clinical and molecular teratology》2009,85(10):811-821
BACKGROUND: Genetic skeletal disorders of the fetus and infant are a large group of genetic disorders, comprising the groups formerly assigned as skeletal dysplasias (osteochondrodysplasias), dysostoses, and malformation syndromes with a skeletal component. Genetic skeletal disorders may be prenatally detected by ultrasonography or result in intrauterine or early postnatal death, constituting one difficult diagnostic field met by the pathologist who performs the perinatal autopsy. METHODS: In this retrospective study, we have gathered radiologic, physical, histopathologic, and molecular data regarding 41 cases of genetic skeletal disorders diagnosed among 1980 fetal and perinatal autopsies over a 10‐year period. RESULTS: Our series of cases were classified according to the 2006 Nosology and Classification of Genetic Skeletal Disorders. The overall frequency of genetic skeletal disorders was 1:48 autopsies. The FGFR3 group and osteogenesis imperfecta type 2 were the more frequently encountered disorders. The mean gestational age at autopsy was 21.9 weeks (range, 12–37 weeks). A final diagnosis was obtained in 95% of cases. Genetic skeletal disorders were detected by prenatal ultrasound in 90% of cases, with a correct typing of the disorder achieved in only 34%. Molecular analysis was confirmative in 5 cases. CONCLUSIONS: The central role of the perinatal pathologist in collaboration with specialized services is essential for the correct interpretation of the radiologic, physical, and histopathologic findings, to accurately classify specific types of genetic skeletal disorders and enable genetic counseling. Birth Defects Research (Part A), 2009. © 2009 Wiley‐Liss, Inc. 相似文献