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221.
Isabel A. Abreu Diane E. Cabelli 《Biochimica et Biophysica Acta - Proteins and Proteomics》2010,1804(2):263-274
Superoxide dismutases are enzymes that function to catalytically convert superoxide radical to oxygen and hydrogen peroxide. These enzymes carry out catalysis at near diffusion controlled rate constants via a general mechanism that involves the sequential reduction and oxidation of the metal center, with the concomitant oxidation and reduction of superoxide radicals. That the catalytically active metal can be copper, iron, manganese or, recently, nickel is one of the fascinating features of this class of enzymes. In this review, we describe these enzymes in terms of the details of their catalytic properties, with an emphasis on the mechanistic differences between the enzymes. The focus here will be concentrated mainly on two of these enzymes, copper, zinc superoxide dismutase and manganese superoxide dismutase, and some relatively subtle variations in the mechanisms by which they function. 相似文献
222.
M.J. Cardador M. Gallego 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2010,878(21):1824-1830
Haloacetic acids (HAAs) are water disinfection byproducts (DBPs) formed by the reaction of chlorine oxidizing compounds with natural organic matter in water containing bromine. HAAs are second to trihalomethanes as the most commonly detected DBPs in surface drinking water and swimming pools. After oral exposure (drinking, showering, bathing and swimming), HAAs are rapidly absorbed from the gastrointestinal tract and excreted in urine. Typical methods used to determine these compounds in urine (mainly from rodents) only deal with one or two HAAs and their sensitivity is inadequate to determine HAA levels in human urine, even those manual sample preparation protocols which are complex, costly, and neither handy nor amenable to automation. In the present communication, we report on a sensitive and straightforward method to determine the nine HAAs in human urine using static headspace (HS) coupled with GC–MS. Important parameters controlling derivatisation and HS extraction were optimised to obtain the highest sensitivity: 120 μl of dimethylsulphate and 100 μl of tetrabutylammonium hydrogen sulphate (derivatisation regents) were selected, along with an excess of Na2SO4 (6 g per 12 ml of urine), an oven temperature of 70 °C and an equilibration time of 20 min. The method developed renders an efficient tool for the precise and sensitive determination of the nine HAAs in human urine (RSDs ranging from 6 to 11%, whereas LODs ranged from 0.01 to 0.1 μg/l). The method was applied in the determination of HAAs in urine from swimmers in an indoor swimming pool, as well as in that of non-swimmers. HAAs were not detected in the urine samples from non-swimmers and those of volunteers before their swims; therefore, the concentrations found after exposure were directly related to the swimming activity. The amounts of MCAA, DCAA and TCAA excreted from all swimmers are related to the highest levels in the swimming pool water. 相似文献
223.
224.
The aim of our study was to examine the effect of mass‐rearing, in which there is no exposure to predators, on antipredator traits of insects for improving sterile insect technique programs. The duration of death‐feigning (antipredator behaviour) in sweet potato weevil Cylas formicarius (Summers) (Coleoptera: Brentidae) after mass‐rearing for 71 generations were compared with those in wild strain. There was no significant difference in the duration of death‐feigning between wild and mass‐reared strains. This indicated that the death‐feigning behaviour of mass‐reared strain was maintained for 71 generations even in the absence of predators. We discuss the reasons why death‐feigning behaviour is maintained after mass‐rearing. 相似文献
225.
Mass‐reared sterile tephritid flies released in sterile insect technique (SIT) programmes exhibit behaviour, physiology and longevity that often differ from their wild counterparts. In the present study, video recordings of flies in laboratory cages are used to determine whether the sequential processes of mass‐rearing and sterilization (using gamma radiation) that are integral to SIT affect general activity patterns of male and female Queensland fruit flies Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) (‘Q‐flies'). Compared with wild flies, mass‐reared flies exhibit a marked reduction in overall activity, and further reduction is found after sterilization. In terms of the frequency of activities, both fertile and sterile mass‐reared Q‐flies fly less often and exhibit more bouts of inactivity and grooming than wild Q‐flies. In addition, in terms of the duration of activities, fertile and sterile mass‐reared Q‐flies spend less time flying and more time walking, grooming and being inactive than wild Q‐flies. Although fertile and sterile mass‐reared flies are similar in other regards, sterile mass‐reared flies spend more time being inactive than fertile mass‐reared flies. These findings raise new questions about how changes in behaviour and activity levels may influence the performance of mass‐reared sterile Q‐flies in the field, as well as the physiological and metabolic processes that are involved. The frequency and duration of inactivity could provide a simple but powerful and biologically relevant test for quality in mass‐rearing and SIT programs. 相似文献
226.
Electrical excitability and signalling, frequently associated with rapid responses to environmental stimuli, are well known in some algae and higher plants. The presence of electrical signals, such as action potentials (AP), in both animal and plant cells suggested that plant cells, too, make use of ion channels to transmit information over long distances. In the light of rapid progress in plant biology during the past decade, the assumption that electrical signals do not only trigger rapid leaf movements in 'sensitive' plants such as Mimosa pudica or Dionaea muscipula, but also physiological processes in ordinary plants proved to be correct. Summarizing recent progress in the field of electrical signalling in plants, the present review will focus on the generation and propagation of various electrical signals, their ways of transmission within the plant body and various physiological effects. 相似文献
227.
228.
Binder H 《European biophysics journal : EBJ》2007,36(4-5):265-279
The ordering and H-bonding characteristics of the hydration water of the lipid 1-palmitoyl-2-oleoylphosphatidylcholine (POPC)
were studied using polarized infrared spectroscopy by varying either the temperature or the relative humidity of the ambient
atmosphere of multibilayer samples. The OH-stretching band of lipid-bound water was interpreted by a simplified two-state
model of well-structured, low density “network” water and of less-structured dense “multimer” water. The IR-spectroscopic
data reflect a rather continuous change of the water properties with increasing distance from the membrane and with changing
temperature. Network and multimer water distribute across the whole polar interphase with changing composition and orientation.
Upon dehydration the fraction of network water increases from about 30 to 60%, a value which is similar to that in supercooled
water at −25°C. The highly ordered gel phase gives rise to an increased fraction of structured network water compared with
the liquid crystalline phase. The IR order parameter shows that the water dipoles rearrange from a more parallel towards a
more perpendicular orientation with respect to the membrane normal with progressive hydration.
Dedicated to Prof. K. Arnold on the occasion of his 65th birthday. 相似文献
229.
By single sensillum tip recording technique, in addition to the salt and pH cells found in antennal taste sensilla of some ground beetles earlier, the third chemosensory cell of four innervating these large sensilla was electrophysiologically identified as a sugar cell in the ground beetle Pterostichus aethiops. This cell generated action potentials of considerably smaller amplitude than those of the salt and pH cells, and phasic-tonically responded to sucrose and glucose over the range of 1-1000 mM tested. Responses were concentration dependent, with sucrose generating more spikes than glucose. During the first second of the response, maximum rates of firing of the sugar cell reached up to 19 and 37 imp/s when stimulated with 1000 mM glucose and sucrose, respectively. Three to four seconds later, the responses decreased close to zero. Both sugars are important in plant carbohydrate metabolism. These ground dwelling insects may come into contact with live and decayed plant material everywhere in their habitat including their preferred overwintering sites in brown-rot decayed wood. In conclusion, we hypothesize that high content of soluble sugars in their overwintering sites and refugia is unfavourable for these ground beetles, most probably to avoid contact with dangerous fungi. 相似文献
230.
Wei SP Li XQ Chou CF Liang YY Peng JB Warnock DG Ma HP 《The Journal of membrane biology》2007,220(1-3):21-31
We used patch-clamp techniques and A6 distal nephron cells as a model to determine how cholesterol regulates the renal epithelial
sodium channel (ENaC). We found that luminal methyl-β-cyclodextrin (mβCD, a cholesterol scavenger) did not acutely affect
ENaC activity at a previously used concentration of 10 mm but significantly decreased ENaC activity both when the cell membrane was stretched and at a higher concentration of 50 mm. Luminal cholesterol had no effect on ENaC activity at a concentration of 50 μg/ml but significantly increased ENaC activity
both when the cell membrane was stretched and at a higher concentration of 200 μg/ml. Confocal microscopy data indicate that
membrane tension facilitates both mβCD extraction of cholesterol and A6 cell uptake of exogenous cholesterol. Together with
previous findings that cholesterol in the apical membrane is tightly packed with sphingolipids and that stretch can affect
lipid distribution, our data suggest that membrane tension modulates the effects of mβCD and cholesterol on ENaC activity,
probably by facilitating both extraction and enrichment of apical cholesterol. 相似文献