Cholinesterases characteristics

Biosensors ai e widely used to the detection of hazardous contaminants in foodstuffs, soil and fresh waters. Due to high sensitivity, simple design, low cost and real-time measurement mode biosensors ai e considered as an alternative to conventional analytical techniques, e.g. GC or HPLC. Although the sensitivity and selectivity of contaminant detection is mainly determined by a biological component, i.e. enzyme or antibodies, the biosensor performance can be efficiently controlled by the optimization of its assembly and working conditions. In this report, the prospects to the improvement of pesticide detection with cholinesterase sensors based on modified screen-printed electrodes are summarized. The following opportunities for the controlled improvement of analytical characteristics of anticholinesterase pesticides ai e discussed ... 

To test this possibility, they first examined the effect of phosphorofluoridates on isolated rabbit s intestine. On such a preparation the action of drugs, like acetylcholine, which act directly on the muscle differs characteristically from the action of those, like eserine, which act by inhibition of cholinesterase activity. The directly acting drugs produce an immediate contraction which proceeds rapidly to a maximum, and after the drug has been washed out the muscle again quickly relaxes. The contraction produced by cholinesterase-inhibiting drugs, such as... 

Physostigmine is an interesting alkaloid because it is generally recognized that it acts by inhibiting a specific enzyme, cholinesterase. This enzyme has been found to be at characteristic levels in the corpuscles and blood plasma of different individuals (p. 79), and it would be expected that the action of the alkaloid in different individ-... 

Almkvist, O., Jelic, V., Amberla, K., Hellstrom-Lindahl, E., MeurUng, L., Nordberg, A. (2001) Responder characteristics to a single oral dose of cholinesterase inhibitor a doubleblind placebo-controlled study with tacrine in Alzheimer patients. Dement. Geriatr. Cogn. Disord., 12, 22-32. 

Castro found DM and CS to be active Inhibitors of cholinesterase and suggested that this characteristic might explain their lacrlmatory effect. Roberts et al. demonstrated a direct effect of DM on gastric activity and, like Striker et al., H 12 found solid evidence that its lethal effects are of respiratory origin. 

Thus, the biochemical characteristics affecting the reactivation of cholinesterase are complex and only partially understood. Knowledge of the kinetics of the various rate-determining processes is essential to the understanding of the inhibitor-reactivation process. 

The nature of the configuration is the basis upon which local anaesthetics are classified. Ester local anaesthetics are characteristically unstable compounds that are broken down in the plasma by plasma cholinesterases. In contrast, the amide agents are very stable compounds that require extensive hepatic biotransformation. The more complex the linkage, the greater the tendency for toxicity. 

In this respect, the most important information has been obtained from the effect of pH changes on enzymic activity. In Fig. 2 the pH-activity curves are represented for true cholinesterase (from Torpedo marmorata) and pseudo-ChE (from human serum), with ACh as substrate. The two curves are not only similar to each other, but also to the curves, characteristic for other, unspecific esterases (37). For the correct interpretation of such curves, it is important to make sure that only the protein in the... 

Both the toxicodynamics and toxicokinetics of OP nerve agents can be explained by their biochemical characteristics of interacting with cholinesterases and other hydrolases. Inhibition of cholinesterases in the blood is the first target for OPs according to the principle of first come, first served (Benschop and de Jong, 2001). 

Pseudocholinesterase deficiency. The neuromuscular blocking action of suxamethonium is terminated by plasma pseudocholinesterase. True cholinesterase (acetylcholinesterase) hydrolyses acetylcholine released by nerve endings, whereas various tissues and plasma contain other nonspecific, hence pseudo, esterases. Affected individuals form so little plasma pseudocholinesterase that metabolism of suxamethonium is seriously reduced. The deficiency characteristically comes to light when a patient fails to breathe spontaneously after a surgical operation, and assisted ventilation may have to be undertaken for hours. Relatives of an affected individual—for this as for other inherited abnormalities carrying avoidable risk—should be sought out, checked to assess their own risk, and told of the result. The prevalence of pseudocholinesterase deficiency in the UK population is about 1 in 2500. 

Cholinesterase inhibition can sometimes persist for weeks thus, repeated exposures to small amounts of this material may result in accumulation of acetylcholinesterase inhibition with possible sudden-onset acute toxicity. Chlorpyrifos may be capable of causing organophosphate-induced delayed neurotoxicity in humans a massive overdose resulted in signs characteristic of delayed neurotoxicity. Animal studies generally indicate, however, that doses several times higher than the LD50 would be required to initiate delayed neurotoxicity. 

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