The influence of four pesticides (atrazine, carbaryl, glyphosate and paraquat) on the catalytic behaviour of invertase, either free, immobilized on inorganic and organic soil colloids or in soils, was investigated. Invertase was immobilized on a clean clay (montmorillonite), an organic compound (tannic acid), and on synthetic organo-mineral [Al(OH)x-tannate and Al(OH)x-tannate-montmorillonite] complexes. Soils with different physico-chemical properties were utilized. The effects of pesticides on invertase performance depended not only on the nature of the pesticide but also on the “status” of the enzyme, i.e. if free, immobilized or in soil. Glyphosate and paraquat enhanced the activity of invertase either free or immobilized on montmorillonite and both pesticides behaved as mixed-type non-essential activators. Activity decreases were instead measured for the enzyme immobilized on organic and organo-mineral matrices. Contrasting results (increases, decreases and no effects) were detected for soil invertase. A general inhibition effect was exhibited by methanol on free, immobilized or soil invertase, but the extent of inhibition depended on the enzyme microenvironment. The addition of atrazine and carbaryl caused partial increases of free and immobilized invertase activity, whereas carbaryl further reduced enzymatic activity in some soils.
[Show abstract][Hide abstract] ABSTRACT: Experiments were conducted to study t he influences of synt hetic bayerite , non2crystalline aluminum ox2 ide (N2AlOH) , goet hite , non2crystalline iron oxide (N2FeOH) and kaolinite on t he adsorption , activit y , ki2 netics and t hermal stabilit y of invertase. Adsorption of invertase on iron , aluminum oxides fitted Langmuir e2 quation. The amount of invertase held on t he minerals followed t he sequence kaolinite > goet hite > N2 AlOH > bayerite > N2FeOH. No correlation was found between enzyme adsorption and t he specific surface area of minerals examined. The differences in t he surface structure of minerals and t he arrangement of enzy2 matic molecules on mineral surfaces led to t he different capacities of minerals for enzyme adsorption. The ad2 sorption of invertase on bayerite , N2AlOH , goet hite , N2FeOH and kaolinite was differently affected by p H. The order for t he activit y of invertase adsorbed on minerals was N2FeOH > N2AlOH > bayerite > reak goet hite > kaolinite. The inhibition effect of minerals on enz yme activity was kaolinite > crystalline oxides > non2crystalline oxides. The p H optimum of iron oxide2 and aluminum oxide2invertase complexes was simi2 lar to t hat of free enzyme (p H 4. 0) , whereas t he p H optimum of kaolinite2inv ertase complex was one p H u2 nit higher t han t hat of free enzyme. The affinity to substrate and t he maximum reaction velocity as well as t he t hermal stabilit y of combined invertase were lower t han t hose of t he free enzyme. Key W ords : enzyme activity , enzyme adsorption , invertase , kaolinite , oxides
[Show abstract][Hide abstract] ABSTRACT: We consider systems for demodulation/modulation which use periodically nonuniform sampling (of arbitrary order) of the bandpass signal to circumvent the carrier-frequency restrictions of uniform sampling. The design of a particular tapped-delay-line (demodulation) or piecewise-constant-impulse-response (modulation) equivalent filter determines both the actual implementation filters and system performance. The tap spacing of the former and the transition times of the latter are periodically nonuniform. Following a characterization of the equivalent filter response, the special case of second-order sampling is examined for insight into the choice of sampling offset. A set of example designs demonstrates that, while nonuniform sampling permits carrier frequencies not allowed with uniform sampling, the resulting system performance is limited by the choice of carrier frequency.
Proceedings - ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing 01/1999; 3:1721-1724. DOI:10.1109/ICASSP.1999.756326
[Show abstract][Hide abstract] ABSTRACT: We assessed the direct and indirect effect of the herbicide glyphosate on soil microbial communities from ponderosa pine (Pinus ponderosa) plantations of varying site quality. Direct, toxic effects were tested using culture media and soil bioassays at glyphosate concentrations up to 100-fold greater than expected following a single field application. Indirect effects on microbial biomass, respiration, and metabolic diversity (Biolog and catabolic response profile) were compared seasonally after 9–13 years of vegetation control using repeated glyphosate applications in a replicated field study. Three pine plantations were selected to provide a range of soil characteristics associated with glyphosate binding (clay, Fe and Al oxide content) and site growing potential from the lowest to the highest in northern California. Glyphosate was toxic to bacteria and fungi from each plantation when grown in soil-free media. Culturable populations were reduced, as was the growth rate and metabolic diversity of surviving bacteria, by increasing concentrations of glyphosate. This toxicity was not expressed when glyphosate was added directly to soil, however. Microbial respiration was unchanged at expected field concentrations (5–50 μg g−1), regardless of soil, and was stimulated by concentrations up to 100-fold greater. Increased microbial activity resulted from utilization of glyphosate as an available carbon substrate. Estimated N and P inputs from glyphosate were inconsequential to microbial activity. Long-term, repeated applications of glyphosate had minimal affect on seasonal microbial characteristics despite substantial changes in vegetation composition and growth. Instead, variation in microbial characteristics was a function of time of year and site quality. Community size, activity, and metabolic diversity generally were greatest in the spring and increased as site quality improved, regardless of herbicide treatment. Our findings suggest that artificial media assays are of limited relevance in predicting glyphosate toxicity to soil organisms and that field rate applications of glyphosate should have little or no affect on soil microbial communities in ponderosa pine plantations.
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