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991.
Summary The concept of random deaths in a computational model for population dynamics is critically examined. We claim that it is
just an artifact, albeit useful, of computational models to limit the size of the populations through the use of the socalled
Verhulst factor and has no biological foundation. Alternative implementations of random deaths strategies are discussed and
compared. 相似文献
992.
M M Fagian L Pereira-da-Silva I S Martins A E Vercesi 《The Journal of biological chemistry》1990,265(32):19955-19960
In a previous report (Macedo, D.V., Ferraz, V. L., Pereira-da-Silva, L., and Vercesi, A. E. (1988) in Integration of Mitochondrial Functions (Lemasters, J. J., et al., eds) pp. 535-542, Plenum Publishing Corp., New York), we proposed that the alterations in the inner mitochondrial membrane permeability caused by Ca2+ plus prooxidants could be the consequence of membrane protein sulfhydryl-disulfide transitions. In this study, we show that Ca2+ plus diamide, a thiol oxidant, significantly decrease the ability of beef heart submitochondrial particles to build up and sustain a membrane potential generated by succinate oxidation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of solubilized membrane proteins indicates that these effects on the membrane potential are associated with the production of protein aggregates due to thiol cross-linking. Evidence is also presented that these protein aggregates can be produced in mitoplasts previously loaded with Ca2+ and that this is potentiated by the presence of either diamide or t-butylhydroperoxide. Furthermore, dithiothreitol, a disulfide reductant, was found to be much more effective than NAD(P)+ reductants in reversing Ca2+ efflux induced by prooxidants. It is concluded that the perturbation of the inner mitochondrial membrane caused by Ca2+ plus prooxidants is associated with protein polymerization due to thiol cross-linking, resulting in the production of high molecular mass protein aggregates. 相似文献
993.
Coupled mitochondria isolated from the white leaves of cabbage (Brassica Oleracea, var. capitata) were inactive in respiration-coupled Ca2+ accumulation, in contrast to mitochondria isolated from etiolated corn (Zea mays) which showed the ability to take up Ca2+ from the medium, although with a much lower activity than liver mitochondria. The addition of corn mitochondria to aerobic medium containing succinate as respiratory substrate and a free Ca2+ concentration of 40 microM resulted in Ca2+ uptake with a decrease in free Ca2+ concentration until a steady state of about 2.0 microM was reached and maintained constant for several minutes. Perturbation of this steady state by the addition of Ca2+ or EGTA was followed by Ca2+ uptake or release, respectively, until the steady state was attained at the original extramitochondrial free Ca2+ concentration. These results indicate that corn but not cabbage mitochondria, as with some animal mitochondria, have the ability to buffer external Ca2+ and may be involved in the maintenance of Ca2+ homeostasis in the cell. 相似文献
994.
995.
DNA damage and lethal effects of hydrogen peroxide and menadione in Chinese hamster cells: distinct mechanisms are involved 总被引:2,自引:0,他引:2
Menadione (Md)-resistant variants of V79 Chinese hamster cells were derived by culturing cells in progressively higher concentrations of this drug. Along with Md resistance these cells acquired cross-resistance to H2O2, which was retained when cells were cultured back in the absence of Md for 18 cell passages. This indicates that some stable alteration is responsible for the modification and may suggest that the toxicity of Md is mediated by oxygen activation. In agreement with the latter a 2.8-fold increase in catalase activity and a 1.5-fold increase in glutathione content were observed in Md-resistant cells as compared to parental cells, whereas superoxide dismutase and glutathione peroxidase remained unaltered. The use of inhibitors of Fenton reaction, inhibitors of enzymatic and nonenzymatic lipid peroxidation and OH radical scavengers, indicated that both DNA damage and cytotoxic effects of H2O2 and Md are mediated by OH radical, without intervention of lipid peroxides. However whereas the catalysis by iron was required for toxicity of extracellular H2O2, it was not involved in Md-induced toxicity. Possible explanations for this difference have been considered, one of them assuming that an excess of the semiquinone form of Md in the cell might replace iron II as a H2O2 reductant, producing OH radical by an organic Fenton reaction. 相似文献
996.
997.
Sequestration of chemical defenses from host plants is a strategy widely used by herbivorous insects to avoid predation. Larvae of the arctiine moth Utetheisa ornatrix feeding on unripe seeds and leaves of many species of Crotalaria (Leguminosae) sequester N-oxides of pyrrolizidine alkaloids (PAs) from these host plants, and transfer them to adults through the pupal stage. PAs confer protection against predation on all life stages of U. ornatrix. As U. ornatrix also uses other Crotalaria species as host plants, we evaluated whether the PA chemical defense against predation is independent of host plant use. We fed larvae from hatching to pupation with either leaves or seeds of one of eight Crotalaria species (C. incana, C. juncea, C. micans, C. ochroleuca, C. pallida, C. paulina, C. spectabilis, and C. vitellina), and tested if adults were preyed upon or released by the orb-weaving spider Nephila clavipes. We found that the protection against the spider was more effective in adults whose larvae fed on seeds, which had a higher PA concentration than leaves. The exceptions were adults from larvae fed on C. paulina, C. spectabilis and C. vitellina leaves, which showed high PA concentrations. With respect to the PA profile, we describe for the first time insect-PAs in U. ornatrix. These PAs, biosynthesized from the necine base retronecine of plant origin, or monocrotaline- and senecionine-type PAs sequestered from host plants, were equally active in moth chemical defense, in a dose-dependent manner. These results are also partially explained by host plant phylogeny, since PAs of the host plants do have a phylogenetic signal (clades with high and low PA concentrations in leaves) which is reflected in the adult defense. 相似文献
998.
999.
Renata Roland Teixeira Miguel Mauricio Díaz Tatiane Vanessa da Silva Santos Jean Tofoles Martins Bernardes Leonardo Gomes Peixoto Olga Lucia Bocanegra Morun Bernardino Neto Foued Salmen Espindola 《PloS one》2015,10(3)
The present study examined the incidence of chronic stress in business executives (109 subjects: 75 male and 34 female) and its relationship with cortisol levels, cognitive performance, and autonomic nervous system (ANS) reactivity after an acute mental stressor. Blood samples were collected from the subjects to measure cortisol concentration. After the sample collection, the subjects completed the Lipp Inventory of Stress Symptoms for Adults and the Stroop Color-Word Test to evaluate stress and cognitive performance levels, respectively. Saliva samples were collected prior to, immediately after, and five minutes after the test. The results revealed that 90.1% of the stressed subjects experienced stress phases that are considered chronic stress. At rest, the subjects with chronic stress showed higher cortisol levels, and no gender differences were observed. No differences were found between the stressed and non-stressed subjects regarding salivary amylase activity prior to test. Chronic stress also impaired performance on the Stroop test, which revealed higher rates of error and longer reaction times in the incongruent stimulus task independently of gender. For the congruent stimulus task of the Stroop test, the stressed males presented a higher rate of errors than the non-stressed males and a longer reaction time than the stressed females. After the acute mental stressor, the non-stressed male group showed an increase in salivary alpha-amylase activity, which returned to the initial values five minutes after the test; this ANS reactivity was not observed in the chronically stressed male subjects. The ANS responses of the non-stressed vs stressed female groups were not different prior to or after the Stroop test. This study is the first to demonstrate a blunted reactivity of the ANS when male subjects with chronic psychological stress were subjected to an acute mental stressor, and this change could contribute to impairments in cognitive performance. 相似文献
1000.
Laiali Jurdi Chaar Tatiana Pereira Alves Alvaro Martins Batista Junior Lisete Compagno Michelini 《PloS one》2015,10(9)