Home About us Contact
|
Home About us Contact | ||
|
|
||
Inhibition Effects (inhibition + effects)
Selected AbstractsCombined effects of the fungicide propiconazole and agricultural runoff sediments on the aquatic bryophyte Vesicularia dubyanaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2005Qinglan Wu Abstract Pesticides, firmly attached to the topsoil, might enter nearby watercourses at periods with high erosive loss of sediments. Therefore, exposure of aquatic organisms to these low mobility pesticides, in many cases, will coincide with a high sediment concentration. In this study, both individual and combined effects of propiconazole and runoff sediment on the aquatic model bryophyte Vesicularia dubyana are studied. Individual exposure to propiconazole induced responses in V. dubyana at rather low concentration levels (,1 ,g/L), showing that harmful effects of propiconazole potentially may occur in watercourses draining propiconazole-treated fields. Individual exposure to the sediment size fractions S1 (0.16,2 ,m) and S2 (0.03,0.16 ,m) caused plant stress at a concentration of 100 mg/L. The coarser fraction S1 showed strong inhibition effects on photosynthesis, probably due to light attenuation. Compared to S1, the suspension with the finer fraction S2 showed lower turbidity, higher nutrient content, and a higher proportion of sediment-bound propiconazole. The combined effects of propiconazole and suspended sediment are dependent on concentrations of sediment and propiconazole. At low sediment concentration (e.g., 100 mg/L), neither S1 nor S2 reduce the toxicity of propiconazole, as only 2% of propiconazole are bound to particles. An increase in sediment concentration decreases the bioavailable concentration of propiconazole; however, at the same time, this increases the turbidity, thereby inhibiting plant photosynthesis. [source] Intermediate accumulation and efficiency of anaerobic digestion treatment of surfactant (alcohol sulfate)-rich wastewater at increasing surfactant/biomass ratiosJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2002Heiko Feitkenhauer Abstract Textile (eg cotton) finishing industry wastewater is characterised by high concentrations of surfactants (up to 2,g,dm,3) and of readily biodegradable biopolymers (COD 5,15,g,dm,3). The anionic surfactant decyl sulfate (DS) was chosen as model surfactant and soluble starch (size) as model compound for the readily biodegradable fraction of the wastewater. Twenty-two batch experiments with increasing DS/biomass ratio (and starch/biomass ratio) were started simultaneously. Biomass concentrations ranged from 50 to 15,000,mg,dm,3. Minor inhibition effects were found for the surfactant degradation itself at all DS/biomass ratios (maximum biodegradation rate 7.7,mgDS gbiomass,1h,1). The starch hydrolysis started without a lag-phase at DS/biomass ratios of up to 0.15,gDS gbiomass,1. The lag-phase was prolonged to about 100,h at a very high DS/biomass ratio (3,gDS gbiomass,1). The relative importance of the accumulated intermediates was dependent on the DS/biomass ratio. Above 0.3,gDS gbiomass,1 10% of the substrate organic carbon accumulated as ethanol, but no ethanol accumulation was observed at low DS/biomass ratios. Moderate DS/biomass ratios caused a considerable delay of the methanogenesis; high DS/biomass ratios prevented the methanogenesis almost completely. © 2002 Society of Chemical Industry [source] Scirpusin A, a hydroxystilbene dimer from Xinjiang wine grape, acts as an effective singlet oxygen quencher and DNA damage protectorJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 5 2010Qingjun Kong Abstract BACKGROUND: Grapes and red wines are rich sources of phenolic compounds such as anthocyanins, catechins, flavonols and stilbenes, most of which are potent antioxidants showing cardioprotective properties. We first isolated scirpusin A, a hydroxystilbene dimer, from a wine grape of Xinjiang, and studied its antioxidant activity. RESULTS: Reactive oxygen species scavenging effects and the protection against reactive singlet oxygen-induced DNA damage of scirpusin A have been investigated in our experiments. The concentration of scirpusin A required to inhibit 50% of 1O2 generation was 17 µmol L,1, while addition of scirpusin A at 140 µmol L,1 caused complete inhibition. Further kinetic study revealed that the reaction of Scirpusin A with singlet oxygen has an extremely high rate constant (ka = 4.68 × 109 L mol,1 s,1). Scirpusin A (140 µmol L,1) exhibited significant inhibition effects on pBR322 DNA breakage. However, scavenging effects of scirpusin A on superoxide anion O2,, and hydroxyl radical ·OH were not potent as the inhibitor rates at a concentration of 1400 µmol L,1 were 28.83% and 19.5%, respectively. CONCLUSION: The present study shows that scirpusin A is a selective quencher of singlet oxygen and a protector against reactive singlet oxygen-induced pBR322 DNA damage at very low concentrations. Copyright © 2010 Society of Chemical Industry [source] Ortho Effects in Quantitative Structure Activity Relationships for Lipase Inhibition by Aryl CarbamatesMOLECULAR INFORMATICS, Issue 8 2003Gialih Lin Abstract Ortho -substituted phenyl- N -butyl carbamates (1,11) are synthesized and evaluated for their inhibition effects on Pseudomonas species lipase. Carbamates 1,11 are characterized as pseudo-substrate inhibitors of the enzyme. The logarithms of dissociation constant (Ki), carbamylation constant (k2), and bimolecular inhibition constant (ki) multiply linearly correlate with Hammett substituent constant (,), Taft-Kutter-Hansch ortho steric constant (ES), and Swan-Lupton field constant (F). For ,logKi -, logk2 -, and logki -correlations, values of ,, ,, f, ,XR are 0.2, ,0.06, ,1.7, 0.8; 0.0, 0.0, 1.0, ,0.07; and ,1.8, 7, 0.6, 5; respectively. The enzyme inhibition mechanism is composed of four steps: 1) the first step which is protonation of carbamates 1,11, 2) the second step (Ki1) which involves in the proton 1,3-shift of protonated carbamates 1,11 then the pseudo- trans to cis conformational change, 3) the third step (Ki2) which is formation of a negative charged enzyme-inhibitor tetrahedral intermediate, and 4) the fourth step (k2) which is the carbamylation step. The former three steps are likely composed of the Ki step. There is little ortho steric enhancement effect in the Ki step. From cross-interaction correlations, distance between carbamate and phenyl substituents in transition state for the Ki step is relatively short due to a large ,XR value of 7. The k2 step is insensitive to ortho steric effect. The k2 step involves in departure of leaving group, substituted phenol in which is protonated from the proton 1,3-shift but not from the active site histidine of the enzyme. From cross-interaction correlations, the distance between carbamate and phenyl substituents in transition state for the k2 step is relatively long due to a small ,XR value of 0.6. [source] Independence of valence modulation and prepulse inhibition of startlePSYCHOPHYSIOLOGY, Issue 1 2000Larry W. Hawk This study sought to determine whether prepulse inhibition and valence modulation of startle are independent, both within and across individuals. Acoustic probes (105 dB) were delivered as 68 undergraduates viewed pleasant, neutral, and unpleasant pictures. Weak acoustic stimuli (8 dB above background) preceded half of the probes by 120 ms. As expected, startles were larger during unpleasant than during pleasant pictures, and smaller on prepulse than no-prepulse trials. In general, valence modulation and prepulse inhibition of startle were unrelated. That is, prepulse inhibition was consistent across affective states, valence modulation did not differ between no-prepulse and prepulse trials, and valence modulation and prepulse inhibition effects were uncorrelated across individuals. Analysis of raw and percent modification scores generally led to similar conclusions. It is concluded that valence modulation and prepulse inhibition are independent startle modulatory phenomena, although this conclusion is tempered by a finding of poor internal consistency reliability for valence modulation. [source] Biokinetic models for representing the complete inhibition of microbial activity at high substrate concentrationsBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2001Gunaseelan Alagappan Abstract This paper reintroduces the Wayman and Tseng model for representing substrate inhibition effects on specific growth rate by further documenting its potential predictive capabilities. It also introduces a modification to this model in which an Andrews inhibition function is used in place of the Monod noninhibitory substrate function. This modification better represents the relationship between specific growth rate and substrate concentration for those substrates that show Andrews type inhibition at lower substrate concentrations, rather than the Monod type noninhibitory behavior described in the model of Wayman and Tseng. Results from nonlinear, least squares regression analysis are used to evaluate the ability of these models to empirically represent experimental data (both new and from the literature). The statistical goodness of fit is evaluated by comparing the regression results against those obtained using other empirical models. Finally, possible mechanisms of toxicity responsible for the observed inhibition trends are used to further justify use of these empirical models. The dominant mechanism considered to be relevant for conceptually explaining complete inhibition at high concentrations of solvents is the deterioration of cell membrane integrity. Literature citations are used to support this argument. This work should lead to improvements in the mathematical modeling of contaminant fate and transport in the environment and in the simulation of microbial growth and organic compound biodegradation in engineered systems. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 75: 393,405, 2001. [source] | |||||||||||||