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61.
Sensory systems have mechanisms to respond to the external environment and adapt to them. Such adaptive responses are effective for a wide dynamic range of sensing and perception of temporal change in stimulus. However, noise generated by the adaptation system itself as well as extrinsic noise in sensory inputs may impose a limit on the ability of adaptation systems. The relation between response and noise is well understood for equilibrium systems in the form of fluctuation response relation. However, the relation for nonequilibrium systems, including adaptive systems, are poorly understood. Here, we systematically explore such a relation between response and fluctuation in adaptation systems. We study the two network motifs, incoherent feedforward loops (iFFL) and negative feedback loops (nFBL), that can achieve perfect adaptation. We find that the response magnitude in adaption systems is limited by its intrinsic noise, implying that higher response would have higher noise component as well. Comparing the relation of response and noise in iFFL and nFBL, we show that whereas iFFL exhibits adaptation over a wider parameter range, nFBL offers higher response to noise ratio than iFFL. We also identify the condition that yields the upper limit of response for both network motifs. These results may explain the reason of why nFBL seems to be more abundant in nature for the implementation of adaption systems. 相似文献
62.
Reuben Clements Darmaraj Mark Rayan Abdul Wahab Ahmad Zafir Arun Venkataraman Raymond Alfred Junaidi Payne Laurentius Ambu Dionysius Shankar Kumar Sharma 《Biodiversity and Conservation》2010,19(4):1115-1136
Three of Malaysia’s endangered large mammal species are experiencing contrasting futures. Populations of the Sumatran rhino
(Dicerorhinus sumatrensis) have dwindled to critically low numbers in Peninsular Malaysia (current estimates need to be revised) and the state of Sabah
(less than 40 individuals estimated). In the latter region, a bold intervention involving the translocation of isolated rhinos
is being developed to concentrate them into a protected area to improve reproduction success rates. For the Asian elephant
(Elephas maximus), recently established baselines for Peninsular Malaysia (0.09 elephants/km2 estimated from one site) and Sabah (between 0.56 and 2.15 elephants/km2 estimated from four sites) seem to indicate globally significant populations based on dung count surveys. Similar surveys
are required to monitor elephant population trends at these sites and to determine baselines elsewhere. The population status
of the Malayan tiger (Panthera tigris jacksoni) in Peninsular Malaysia, however, remains uncertain as only a couple of scientifically defensible camera-trapping surveys
(1.66 and 2.59 tigers/100 km2 estimated from two sites) have been conducted to date. As conservation resources are limited, it may be prudent to focus
tiger monitoring and protection efforts in priority areas identified by the National Tiger Action Plan for Malaysia. Apart
from reviewing the conservation status of rhinos, elephants and tigers and threats facing them, we highlight existing and
novel conservation initiatives, policies and frameworks that can help secure the long-term future of these iconic species
in Malaysia. 相似文献
63.
Girijavallabhan VM Chen L Dai C Feltz RJ Firmansjah L Li D Kim SH Kozlowski JA Lavey BJ Kosinski A Piwinski JJ Popovici-Muller J Rizvi R Rosner KE Shankar BB Shih NY Siddiqui MA Tong L Wong MK Yang DY Yang L Yu W Zhou G Guo Z Orth P Madison V Bian H Lundell D Niu X Shah H Sun J Umland S 《Bioorganic & medicinal chemistry letters》2010,20(24):7283-7287
Our research on hydantoin based TNF-α converting enzyme (TACE) inhibitors has led to an acetylene containing series that demonstrates sub-nanomolar potency (K(i)) as well as excellent activity in human whole blood. These studies led to the discovery of highly potent TACE inhibitors with good DMPK profiles. 相似文献
64.
Jatinder Kaur Mukker Valeriya Kotlyarova Ravi Shankar Prasad Singh Jane Alcorn 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2010,878(30):3076-3082
We report a rapid and simple HPLC method with fluorescence detection for the quantification of the major flaxseed lignan, secoisolarisiresinol diglucoside (SDG) and its major metabolites. The method is specific for SDG, secoisolarisiresinol (SECO), enterodiol (ED) and entrolactone (EL) in rat serum. The assay procedure involves chromatographic separation using a Waters Symmetry C18 reversed-phase column (4.6 mm × 150 mm, 5 μm) and mobile phase gradient conditions consisting of acetonitrile (0.1% formic acid) and water (0.1% formic acid). SDG extraction from serum requires the use of Centrifuge filters while SECO, ED and EL are extracted with diethyl ether. The organic layer is evaporated and reconstituted in 100 μL of mobile phase and 50 μL of reconstituted sample or filtrate is injected onto the column. Total run time is 25 min. Calibration curves are linear (r2 ≥ 0.997) from 0.05 to 10 μg/mL for SDG and EL and 0.01–10 μg/mL for SECO and ED. Precision and accuracy are within USFDA specified limits. The stability of all lignans is established in auto-injector, bench-top, freeze–thaw and long-term stability at −80 °C for 30 days. The method's reasonable sensitivity and reliance on more widely available HPLC technology should allow for its straightforward application to pharmacokinetic evaluations of lignans in animal model systems such as the rat. 相似文献
65.
The present study investigates the efficiency of Aspergillus niger to produce invertase, an industrially important enzyme by using powdered stem of Cympopogan caecius (Lemon grass) as sole substrate and sole carbon source for the microorganism. The molecular weight of invertase was estimated
to be 66–70 kDa by sodium do decyl sulphate poly acrylamide gel electrophoresis (SDS PAGE). The production of the enzyme was
studied at different pH scales ranging from pH 4.0 to 7.0 at a constant temperature of 30°C and 2% substrate concentration.
The maximum production of invertase (specific activity −0.0516 μk/mg protein) was obtained at pH 5.5 at 30°C temperature,
and incubation for 48 h. The activity was found to be stable at pH 5.5 for 30 min. The enzyme was found to be stable in the
temperature range of 20–55°C. The effect of divalent metal ions Cu2+, Fe2+, Co2+ on the activity of the enzyme invertase showed that these ions affected the activity by a certain factor. The study can be
further industrially exploited in a country-like India where lemon grass is found in plenty and can be used as substrate for
enzyme production. Moreover, the preparation of the substrate is also a simple process. 相似文献
66.
Crude xylanase from Aspergillus sydowii SBS 45 was tested for enzymatic bleaching of kraft (Decker) pulp. After optimization of three parameters, consistency of pulp, retention time and enzyme dose, considerable increase in the release of UV and visible absorbance spectra of materials and reducing sugars was observed, which clearly indicated the action of xylanase on pulp. Final brightness of pulp was increased from 29.42 to 70.42% and kappa number was reduced from 15.93 to 1.61, when 25 U of xylanase was given with a retention time of 5 h and at a consistency of 10%. When 10 U g−1 xylanase was given, 14.3% elemental chlorine and 14.3% H2O2 could be reduced and when 25 U g−1 xylanase was given 14.3% elemental chlorine and 28.6% H 2O2 could be reduced thereby retaining the brightness at control level. 相似文献
67.
Cortisol (20, 40 and 60 micrograms/fish for 10 days) treatment caused an increase in testicular-somatic index (TSI) in immature N. notopterus whereas in mature fish no change from that of controls was observed. Histology of testis indicated that spermatogenetic activity was activated in immature fish while it was inhibited in mature fish. Testicular cholesterol exhibited a similar response. The results indicate that cortisol inhibits spermatogenesis during mature phase while it promotes spermatogenesis during immature phase of the reproductive cycle in N. notopterus. 相似文献
68.
One hundred and forty two cotton germplasm lines were screened for cotton leaf curl virus symptoms in field evaluations during 2003, 2004, and 2005. Fifty cross combinations involving 30 of these lines classified resistant or susceptible were used for inheritance study of the disease. All the F(1) plants of crosses involving resistant x resistant, resistant x susceptible, and susceptible x resistant parents were resistant, indicating dominant expression of the disease resistance and there were no maternal or cytoplasmic effects detected from reciprocal hybridization. In 22 crosses, 4 types of segregation patterns were obtained in the F(2) generations. A good fit for 15 (resistant):1 (susceptible), 13 (resistant):3 (susceptible), 9 (resistant):7 (susceptible) ratios indicated digenic control of the trait with duplicate dominant, dominant inhibitory, and duplicate recessive epistasis, respectively. Three-gene control with triplicate dominant epistasis was obtained in one of the crosses. This segregation pattern, however, needs further confirmation due to smaller population size. The absence of complementary gene action was obtained in 1 susceptible x susceptible and 27 resistant x resistant crosses as their F(1)s were susceptible and resistant, respectively, and F(2) generation lacked segregation. 相似文献
69.
Gowri Shankar BA Sarani R Michael D Mridula P Ranjani CV Sowmiya G Vasundhar B Sudha P Jeyakanthan J Velmurugan D Sekar K 《Journal of biosciences》2007,32(4):693-704
Ion pairs contribute to several functions including the activity of catalytic triads, fusion of viral membranes, stability in thermophilic proteins and solvent-protein interactions. Furthermore, they have the ability to affect the stability of protein structures and are also a part of the forces that act to hold monomers together. This paper deals with the possible ion pair combinations and networks in 25% and 90% non-redundant protein chains. Different types of ion pairs present in various secondary structural elements are analysed. The ion pairs existing between different subunits of multisubunit protein structures are also computed and the results of various analyses are presented in detail. The protein structures used in the analysis are solved using X-ray crystallography, whose resolution is better than or equal to 1.5 A and R-factor better than or equal to 20%. This study can, therefore, be useful for analyses of many protein functions. It also provides insights into the better understanding of the architecture of protein structure. 相似文献
70.
G-quadruplexes in promoters throughout the human genome 总被引:22,自引:11,他引:11