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91.
Bruce S. Jacobson George G. Laties Bruce N. Smith Samuel Epstein Betsy Laties 《BBA》1970,216(2):295-304
The respiration of thin aerated discs of potato tuber tissue rises sigmoidally through 24 h. Aged disc respiration is ostensibly resistant to concentrations of cyanide which inhibit the respiration of fresh discs. It has been shown that cyanide-resistant respiration does not represent indifference to the inhibitor, but is rather due to the suppression of one respiratory carbon path and the evocation of another. The predominant respiratory carbon path of aged discs in the absence of cyanide comprises glycolysis linked to the tricarboxylic acid cycle. The carbon path mediating the cyanide-induced respiration reflects tricarboxylic acid cycle-independent lipid degradation.
The respiratory substrate at any time was deduced by comparing the 13C/12C ratio of respired CO2, collected from discs in the presence or absence of cyanide, with the 13C/12C ratios characterizing endogenous potential metabolites. The determination of the predominant respiratory substrate in potato discs, which have an endogenous substrate reserve, proved possible because the relative concentrations of the stable carbon isotopes in endogenous compounds such as lipid and starch are widely different. 相似文献
92.
Norah E. M. Brown Marco Milazzo Samuel P. S. Rastrick Jason M. Hall‐Spencer Thomas W. Therriault Christopher D. G. Harley 《Global Change Biology》2018,24(1):e112-e127
Ocean acidification may have far‐reaching consequences for marine community and ecosystem dynamics, but its full impacts remain poorly understood due to the difficulty of manipulating pCO2 at the ecosystem level to mimic realistic fluctuations that occur on a number of different timescales. It is especially unclear how quickly communities at various stages of development respond to intermediate‐scale pCO2 change and, if high pCO2 is relieved mid‐succession, whether past acidification effects persist, are reversed by alleviation of pCO2 stress, or are worsened by departures from prior high pCO2 conditions to which organisms had acclimatized. Here, we used reciprocal transplant experiments along a shallow water volcanic pCO2 gradient to assess the importance of the timing and duration of high pCO2 exposure (i.e., discrete events at different stages of successional development vs. continuous exposure) on patterns of colonization and succession in a benthic fouling community. We show that succession at the acidified site was initially delayed (less community change by 8 weeks) but then caught up over the next 4 weeks. These changes in succession led to homogenization of communities maintained in or transplanted to acidified conditions, and altered community structure in ways that reflected both short‐ and longer‐term acidification history. These community shifts are likely a result of interspecific variability in response to increased pCO2 and changes in species interactions. High pCO2 altered biofilm development, allowing serpulids to do best at the acidified site by the end of the experiment, although early (pretransplant) negative effects of pCO2 on recruitment of these worms were still detectable. The ascidians Diplosoma sp. and Botryllus sp. settled later and were more tolerant to acidification. Overall, transient and persistent acidification‐driven changes in the biofouling community, via both past and more recent exposure, could have important implications for ecosystem function and food web dynamics. 相似文献
93.
Tetrathionate enrichment broth is a complex mixture of salts including iodides and other polythionates, but only thiosulfate (0.0736 m) and tetrathionate (0.0236 m) in combination were toxic for Escherichia coli. Individually, these two salts were not lethal. The lethal action of this thiosulfate-tetrathionate mixture affected only growing cells. A possible relationship between the lethality of the thiosulfate-tetrathionate mixture for a culture and its ability to reduce tetrathionate is suggested. 相似文献
94.
Starch mobilization in leaves 总被引:13,自引:0,他引:13
Starch mobilization is well understood in cereal endosperms, but both the pathway and the regulation of the process are poorly characterized in other types of plant organs. Arabidopsis leaves offer the opportunity for rapid progress in this area, because of the genomic resources available in this species and the ease with which starch synthesis and degradation can be monitored and manipulated. Progress in understanding three aspects of starch degradation is described: the role of disproportionating enzyme, the importance of phosphorolytic degradation, and new evidence about the involvement of a starch-phosphorylating enzyme in the degradative process. Major areas requiring further research are outlined. 相似文献
95.
Samuel Pineda Manuel Medina José I. Figueroa Thomas J. Henry Laura V. Mena Juan M. Chavarrieta 《Biocontrol Science and Technology》2016,26(8):1073-1086
The life cycle and several life parameters of the zoophytophagous predator Engytatus varians (Distant) (Heteroptera: Miridae), including nymphal growth according to Dyar’s rule, were examined in the laboratory. The egg, nymph (five instars), and adult stages were 9.20, 17.36, and 19.02?d in length, respectively. The growth ratio for nymphs was consistent with Dyar’s rule based on the lengths of the femora of the forelegs, the tibiae and femora of the middle legs, and the antennae. Some biological characteristics of E. varians were also evaluated when the mirid was fed three different diets (B. cockerelli third instars, Sitotroga cerealella Olivier [Lepidoptera: Gelechiidae] eggs, and a mixture of both instars and eggs). The length of the nymphal stage was three days longer on a diet of only S. cerealella eggs than when the mirids were fed the third instars of B. cockerelli only or a mixture of both. The sex ratio was not affected by the type of diet. Nymphs of E. varians consumed B. cockerelli nymphs (80–85) when fed third instars only and third instars?+?S. cerealella eggs, respectively. The potential use of this predator as a biological control agent of B. cockerelli is discussed. 相似文献
96.
Experimental evidence is increasingly being used to reassess the quality and accuracy of genome annotation. Proteomics data used for this purpose, called proteogenomics, can alleviate many of the problematic areas of genome annotation, e.g. short protein validation and start site assignment. We performed a proteogenomic analysis of 46 genomes spanning eight bacterial and archaeal phyla across the tree of life. These diverse datasets facilitated the development of a robust approach for proteogenomics that is functional across genomes varying in %GC, gene content, proteomic sampling depth, phylogeny, and genome size. In addition to finding evidence for 682 novel proteins, 1336 new start sites, and numerous dubious genes, we discovered sites of post-translational maturation in the form of proteolytic cleavage of 1175 signal peptides. The number of novel proteins per genome is highly variable (median 7, mean 15, stdev 20). Moreover, comparison of novel genes with the current genes did not reveal any consistent abnormalities. Thus, we conclude that proteogenomics fulfills a yet to be understood deficiency in gene prediction. With the adoption of new sequencing technologies which have higher error rates than Sanger-based methods and the advances in proteomics, proteogenomics may become even more important in the future. 相似文献
97.
Linda S. M. Ooi Wing-Shan Ho Karry L. K. Ngai Li Tian Paul K. S. Chan Samuel S. M. Sun Vincent E. C. Ooi 《Journal of biosciences》2010,35(1):95-103
A mannose-binding lectin (Narcissus tazetta lectin [NTL]) with potent antiviral activity was isolated and purified from the bulbs of the Chinese daffodil Narcissus tazetta var. chinensis, using ion exchange chromatography on diethylaminoethyl (DEAE)-cellulose, affinity chromatography on mannose-agarose and
fast protein liquid chromatography (FPLC)-gel filtration on Superose 12. The purified lectin was shown to have an apparent
molecular mass of 26 kDa by gel filtration and 13 kDa by SDS-PAGE, indicating that it is probably a dimer with two identical
subunits. The cDNA-derived amino acid sequence of NTL as determined by molecular cloning also reveals that NTL protein contains
a mature polypeptide consisting of 105 amino acids and a C-terminal peptide extension. Three-dimensional modelling study demonstrated
that the NTL primary polypeptide contains three subdomains, each with a conserved mannose-binding site. It shows a high homology
of about 60%–80% similarity with the existing monocot mannose-binding lectins. NTL could significantly inhibit plaque formation
by the human respiratory syncytial virus (RSV) with an IC50 of 2.30 μg/ml and exhibit strong antiviral properties against influenza A (H1N1, H3N2, H5N1) and influenza B viruses with
IC50 values ranging from 0.20 μg/ml to 1.33 μg/ml in a dose-dependent manner. It is worth noting that the modes of antiviral action
of NTL against RSV and influenza A virus are significantly different. NTL is effective in the inhibition of RSV during the
whole viral infection cycle, but the antiviral activity of NTL is mainly expressed at the early stage of the viral cycle of
influenza A (H1N1) virus. NTL with a high selective index (SI=CC50/IC50≥141) resulting from its potent antiviral activity and low cytotoxicity demonstrates a potential for biotechnological development
as an antiviral agent. 相似文献
98.
Akira Sassa William A. Beard David D. Shock Samuel H. Wilson 《Journal of visualized experiments : JoVE》2013,(78)
Human 8-oxoguanine DNA glycosylase (OGG1) excises the mutagenic oxidative DNA lesion 8-oxo-7,8-dihydroguanine (8-oxoG) from DNA. Kinetic characterization of OGG1 is undertaken to measure the rates of 8-oxoG excision and product release. When the OGG1 concentration is lower than substrate DNA, time courses of product formation are biphasic; a rapid exponential phase (i.e. burst) of product formation is followed by a linear steady-state phase. The initial burst of product formation corresponds to the concentration of enzyme properly engaged on the substrate, and the burst amplitude depends on the concentration of enzyme. The first-order rate constant of the burst corresponds to the intrinsic rate of 8-oxoG excision and the slower steady-state rate measures the rate of product release (product DNA dissociation rate constant, koff). Here, we describe steady-state, pre-steady-state, and single-turnover approaches to isolate and measure specific steps during OGG1 catalytic cycling. A fluorescent labeled lesion-containing oligonucleotide and purified OGG1 are used to facilitate precise kinetic measurements. Since low enzyme concentrations are used to make steady-state measurements, manual mixing of reagents and quenching of the reaction can be performed to ascertain the steady-state rate (koff). Additionally, extrapolation of the steady-state rate to a point on the ordinate at zero time indicates that a burst of product formation occurred during the first turnover (i.e. y-intercept is positive). The first-order rate constant of the exponential burst phase can be measured using a rapid mixing and quenching technique that examines the amount of product formed at short time intervals (<1 sec) before the steady-state phase and corresponds to the rate of 8-oxoG excision (i.e. chemistry). The chemical step can also be measured using a single-turnover approach where catalytic cycling is prevented by saturating substrate DNA with enzyme (E>S). These approaches can measure elementary rate constants that influence the efficiency of removal of a DNA lesion. 相似文献
99.
100.
Andrew J. Bladon Paul F. Donald Samuel E.I. Jones Nigel J. Collar Jarso Deng Galgalo Dadacha Yilma D. Abebe Rhys E. Green 《Ibis》2019,161(3):546-558
Climate may influence the distribution and abundance of a species through a number of demographic and ecological processes, but the proximate drivers of such responses are only recently being identified. The Ethiopian Bush‐crow Zavattariornis stresemanni is a starling‐like corvid that is restricted to a small region of southern Ethiopia. It is classified as Endangered in the IUCN Red List of globally threatened species. Previous work suggested that this range restriction is almost perfectly defined by a climate envelope that is cooler than surrounding areas, but the proximate mechanism remains unexplained. The heavily altered habitats which the species inhabits are widespread across Africa, and recent work has shown that the Bush‐crow is behaviourally adaptable and has a catholic diet. We assess whether its enigmatic distribution can be explained by behavioural responses to the higher temperatures that surround its current range. Using environmental niche models and field observations of thermally mediated behaviour, we compare the range restriction and behavioural thermoregulation of the Ethiopian Bush‐crow with those of two sympatric control species that are similar in size and ecology, but have much larger ranges that include hotter environments. White‐crowned Starling Lamprotornis albicapillus and Superb Starling L. superbus occupy similar habitats to the Ethiopian Bush‐crow and all three frequently forage together. We found that the Bush‐crow's range is limited primarily by temperature, with a secondary effect of dry season rainfall, whereas the ranges of the two starling species are better predicted by wet season rainfall alone. Bush‐crows exhibited panting behaviour and moved into the shade of trees at significantly lower ambient temperatures than did the starlings, and their food intake declined more steeply with increasing temperature. These results indicate that the limited geographical range of the Bush‐crow reflects an inability to cope with higher temperatures. This suggests that a species' response to climate change might not be easily predicted by its ecological generalism, and may represent an inherited debt from its evolutionary history. 相似文献