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21.
1. Recent observations of actuarial senescence – an increase in mortality rate with age – have challenged the assertion that the brevity of adult insect life spans precludes ageing. 2. Here the rate of senescence in 22 species of Lepidoptera was quantified by fitting demographic models to adult survivorship data drawn from a range of field and laboratory studies. 3. Senescence was evident in all 22 species investigated, with a model of age‐related mortality consistently fitting the survivorship curves significantly better than an alternative model which assumes constant mortality. 4. The rates of senescence varied significantly among species. The rates of senescence also differed significantly between sexes for all species tested, but not in a consistent way. 相似文献
22.
Geoffrey P Dobson 《BBA》2002,1553(3):261-267
Our aim was to estimate a number of bioenergetic parameters in the beating mouse, rat and guinea pig heart in situ and compare the values to those in hearts of mammals over a 2000-fold range in body mass. For the mouse, rat and guinea pig heart, we report a phosphorylation ratio of 1005±50 (n=16), 460±32 (n=10) and 330±22 (n=5) mM−1 and a free cytosolic [ADP] concentration of 13, 18 and 22 μM, respectively. When each parameter was plotted against body mass, they scaled closely to the quarter power (−0.28, r=0.99 and −0.23, r=0.97). A similar regression slope was found when the inverse of free [ADP] was plotted against absolute mitochondrial (slope=−0.26, r=0.99) and myofibrillar volumes (slope=−0.24, r=0.99). The similar slopes indicate that the ratio of absolute mitochondria and myofibrillar volumes in the healthy mammalian heart is a constant, and independent of body size. In conclusion, our study supports the hypothesis that the mammalian heart has a number of highly conserved thermodynamic and kinetic parameters that obey quarter-power laws linking the phosphorylation ratio, ATP turnover rates, free [ADP] and absolute mitochondrial volumes to body size. The results are discussed in terms of possible mechanisms and potential deviations from these laws in some disease states. 相似文献
23.
24.
《Free radical research》2013,47(2):82-88
AbstractEndothelial dysfunction characterized by decreased nitric oxide (NO) bioavailability is the first stage of coronary artery disease. It is known that one of the factors associated with an increased risk of coronary artery disease is a high plasma level of uric acid. However, causative associations between hyperuricaemia and cardiovascular risk have not been definitely proved. In this work, we tested the effect of uric acid on endothelial NO bioavailability. Electrochemical measurement of NO production in acetylcholine-stimulated human umbilical endothelial cells (HUVECs) revealed that uric acid markedly decreases NO release. This finding was confirmed by organ bath experiments on mouse aortic segments. Uric acid dose-dependently reduced endothelium-dependent vasorelaxation. To reveal the mechanism of decreasing NO bioavailability we tested the effect of uric acid on reactive oxygen species production by HUVECs, on arginase activity, and on acetylcholine-induced endothelial NO synthase phosphorylation. It was found that uric acid increases arginase activity and reduces endothelial NO synthase phosphorylation. Interestingly, uric acid significantly increased intracellular superoxide formation. In conclusion, uric acid decreases NO bioavailability by means of multiple mechanisms. This finding supports the idea of a causal association between hyperuricaemia and cardiovascular risk. 相似文献
25.
OKSANA P. ANDRUSHCHYSHYN KEVIN P. WILSON D. DUDLEY WILLIAMS 《Freshwater Biology》2007,52(9):1745-1761
1. Ciliated protozoans (Phylum Ciliophora) were collected from five sites in a shallow groundwater system in southern Ontario, Canada over a 13‐month period: one at the spring source, two along the channel banks, and two in the stream channel. Ciliates and environmental data were collected from surface water and at five depths into the sediment, located at 20, 40, 60, 80 and 100 cm. 2. Species richness was high (170 ciliate species belonging to 89 genera were identified) and variable, both spatially and temporally. Highest species richness (86) occurred between 20 and 60 cm, and typically decreased below 60 cm. 3. Ciliate densities were also seasonally and spatially variable. Densities peaked in March between 40 cm (as high as 69 900 cells L−1) and 60 cm, and again in May and June at 80 and 100 cm. Densities were lowest in winter. The surface‐water ciliate community had a different species composition and lower population densities. 4. At all depths, small (<50 μm) bacterivorous ciliates typically dominated, but omnivorous and predatory species were also present (combined, up to 30% of the average density). 5. Several ciliate genera, traditionally considered planktonic, occurred at low densities from 40 cm down to 100 cm. 6. Ordination analysis indicated that the main factors influencing the shallow groundwater ciliate communities were depth and temperature. 7. Dissolved oxygen also appeared to influence these communities in that they typically comprised genera that preferred either low‐oxygen or anaerobic conditions. 相似文献
26.
1. When dissolved oxygen levels decline in aquatic systems, prey may be unable to maintain behaviours protecting them from predators. We examined how oxygen availability affected anti‐predator responses in the freshwater clam, Corbicula fluminea. 2. When attacked, bivalves protect their soft tissues by closing their protective valves. This reduces vulnerability to small predators, but ventilation and oxygen uptake are suspended. We found that after a simulated attack, clams under low oxygen conditions reopened their valves sooner than clams under high oxygen conditions, suggesting that hypoxia increases vulnerability to predation. 3. Bivalves may also evade predators through burial into the substratum. Deeper burial confers greater refuge from predators, but increases the costs of ventilation. In a second experiment, we studied how burial depth of C. fluminea is affected by oxygen availability. Additionally, we examined whether clams changed burial depth following a simulated attack by a small predator, and whether this response was affected by oxygen availability. Our results offered partial support for the hypothesis that burial depth is reduced under hypoxic conditions, but the simulated attack did not affect burial depth in any oxygen treatments. 相似文献
27.
Abstract. The wood-degrading white-rot fungus Phanerochaete chrysosporium , has been the subject of intensive research in recent years and, based upon isolation of the extracellular enzyme ligninase, major advances have now been made toward elucidating the mechanism by which this fungus degrades lignin. From these developments, a model emerges which could explain the process by which wood-degrading fungi in general, attack lignin. 相似文献
28.
Sudha Rao Gopalakrishna Kamath Gururaj Maralihalli Anil S. Bhagwat 《Photosynthesis research》1987,12(2):155-164
The -aminolevulinic acid dehydratase activity was irreversibly inactivated by irradiation of the enzyme in presence of flavin mononucleotide. The loss of enzyme activity was dependent on time of irradiation, concentration of FMN and intensity of irradiance. It required oxygen and was markedly enhanced in heavy water. The presence of levulinic acid (a competitive inhibitor of -ALAD) during irradiation prevented the inactivation considerably indicating photooxidative damage at or near the active site. Superoxide dismutase, sodium benzoate and sodium formate offered no protection, but singlet oxygen quenchers like azide and tryptophan were effective. NADH, electron donor to excited flavins, also prevented the loss of enzyme activity. These results indicate that singlet oxygen produced by light absorption of FMN was responsible for the photooxidative inhibition of the enzyme.Abbreviations ALAD
-aminolevulinic acid dehydratase
- FMN
flavin mononucleotide
- O2
-
superoxide
- H2O2
hydrogen peroxide
- 102
singlet oxygen
- LA
levulinic acid
- PBG
porphobilinogen
- BSA
bovine serum albumin
- BME
2-mercaptoethanol
- SOD
superoxide dismutase
- pHMB
para-hydroxymercuribenzoate
- DTT
dithiothreitol
- FAD
flavin adenine dinucleotide
- NADH
nicotinamide adenine dinucleotide 相似文献
29.
Summary The maximum density achievable by aquatic organisms is an inverse linear function of their body size. As a consequence, the maximum achievable biomass is independent of body size, and is 2 orders of magnitude higher than the biomass in natural populations. The minimum interorganismic terorganismic distance, calculated from the maximum density to allow comparison between aquatic and terrestrial organisms, scales as the 1/3 power of body size in both habitats. The similarities in the interorganismic distance of terrestrial and aquatic plant and animal communities suggest a fundamental regularity in the way organisms use the space. 相似文献
30.
A. Tyagi J. Hermans J. Steppuhn Ch. Jansson F. Vater R. G. Herrmann 《Molecular & general genetics : MGG》1987,207(2-3):288-293
Summary Several cDNA clones encoding the 33 kDa protein associated with the photosynthetic water oxidation activity of spinach were sequenced. A 1208 bp insert of one of the clones encodes the entire 331 amino acid residues of the precursor protein including 84 amino acids (8.5 kDa) of the amino-terminal transit peptide, 49 bp of the 5 and 111 bp of the 3 untranslated segment of the mRNA. The 3 poly(A) tail starts 19 bp downstream from a putative polyadenylation signal, TATAAA. The hydrophilic mature protein consists of 247 amino acid residues corresponding to an Mr of 26.5 kDa, which is 6.5 kDa smaller than the value determined by SDS-polyacrylamide gel electrophoresis (33–34 kDa), and shows a certain degree of conservation with the putative Mn-complexing active sites of bacterial Mn-dependent superoxide dismutases. The anatomy of the unusually long transit sequence is discussed with regard to current concepts of protein import into and protein routein within the organelle. 相似文献