PubMed · 9451326
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P Lheureux. 1998. Sensitivity, specificity, and predictive values.. https://doi.org/10.1016/s0735-6757(98)90077-8
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The aim of this study was to find a suitable biomarker for pyrethroid adverse effects. It was shown that there is a correlation between the half-life time (t(1/2)) of pyrethroids in plasma and the clinical findings. We hypothized that this finding indicates an interindividual different amount of total esterase activity or even a polymorphism. By in vitro experiments it was demonstrated that pyrethroids are cleaved by carboxylesterases. After it turned out that carboxylesterase activity in human plasma is too low for detection, a method for specific determination of carboxylesterase activity in human isolated lymphocytes was developed. As a substrate for carboxylesterase activity, cyfluthrin was added to the lymphocyte suspension. As a proof for cyfluthrin degradation by carboxylesterases the produced hydrocyanic acid was determined by GC/MS. First hints for interindividual differences in carboxylesterase activity in lymphocytes were found.
Normal, habituated and transformed in vitro tissue lines of sugar beet (Beta vulgaris L.), horseradish (Armoracia lapathifolia Gilib.) and potato (Solanum tuberosum L.) were studied with regard to isoesterase patterns. Isoenzymes were separated in gradient gels (5-12%) of polyacrylamide and by isoelectric focussing in pH range 4-9. 1- and 2-naphtylacetate were used as substrates of broad spectrum which cover also esterases (arylesterases and carboxylesterases) reacting with organophosphorous compounds. Distinct isoesterase patterns were noticed in sugar beet normal, habituated and crown gall tumour tissues. Horseradish tumour and teratoma, on the contrary, differed only in one anodic isoenzyme. Even the malformed shoots and unorganised tissue of teratoma had the same patterns. In potato tuber tissue, change in isoesterase pattern, characterised by disappearance of a dominant dark area, was observed during tumour development. The gradient gels gave more stable and reproducible isoenzyme patterns than isoelectric focussing.
The backbone dynamics of Fusarium solani pisi cutinase in complex with a phosphonate inhibitor has been studied by a variety of nuclear magnetic resonance experiments to probe internal motions on different time scales. The results have been compared with dynamical studies performed on free cutinase. In solution, the enzyme adopts its active conformation only upon binding the inhibitor. While the active site Ser120 is rigidly attached to the stable alpha/beta core of the protein, the remainder of the binding site is very flexible in the free enzyme. The other two active site residues Asp175 and His188 as well as the oxyanion hole residues Ser42 and Gln121 are only restrained into their proper positions upon binding of the substrate-like inhibitor. The flap helix, which opens and closes the binding site in the free molecule, is also fixed in the cutinase-inhibitor complex. Our results are in contrast with the X-ray analysis results, namely that in the protein crystal, free cutinase has a well-defined active site and a preformed oxyanion hole and that it does not need any rearrangements to bind its substrate. Our solution studies show that cutinase does need conformational rearrangements to bind its substrate, which may form the rate-limiting step in catalysis.