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Biomedical subjects

E Reiner

Publications and source records attributed to E Reiner.

At least 73 records · Page 4Linked to original sources
PubMed1977

Competition between substrates for acetylcholinesterase and cholinesterase.

The kinetics of competition of pairs of two substrates for bovine erythrocyte acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) and horse serum cholinesterase (acylcholine acyl-hydrolase, EC 3.1.1.8) was studied so that the hydrolysis of only one substrate was measured at a time. The substrates were acetylthiocholine, were used as competiting substrates i.e. inhibitors. The substrate inhibition constants (Kss) and Michaelis constants for the reaction of a single substrate were also determined. It was concluded that the substrate inhibition site in the enzyme does not show up in the competition between two substrates.

Acetylcholine↗
PubMed1977

Blood levels of chlorinated hydrocarbon residues in the population of a continental town in Croatia (Yugoslavia).

Plasma or serum samples of 147 individuals from the general population of a continental town in Croatia (Yugoslavia) were analyzed for chlorinated hydrocarbons in 1975. The compounds were determined by gas chromatography and identified by comparing their retention times with those of known standards. All samples contained p,p'-DDE; mean concentration was 35.3 ppb. Only 20 samples contained p,p'-DDT; mean concentration was 22.7 ppb. Concentrations of alpha-BHC, lindane, and p,p'-TDE were 3.25, 4.09, and 11.6 ppb, respectively.

Adolescent↗
PubMed1973

Comparison of methods for measuring cholinesterase inhibition by carbamates.

The Acholest and tintometric methods are used widely for measuring blood cholinesterase activity after exposure to organophosphorus compounds. However, if applied for measuring blood cholinesterase activity in persons exposed to carbamates, the accuracy of the methods requires verification since carbamylated cholinesterases are unstable. The spectrophotometric method was used as a reference method and the two field methods were employed under controlled conditions. Human blood cholinesterases were inhibited in vitro by four methylcarbamates that are used as insecticides. When plasma cholinesterase activity was measured by the Acholest and spectrophotometric methods, no difference was found. The enzyme activity in whole blood determined by the tintometric method was </= 11% higher than when the same sample was measured by the spectrophotometric method.

Carbamates↗
PubMed1973

Effect of sample storage on human blood cholinesterase activity after inhibition by carbamates.

During an operational field trial with propoxur it was observed that the inhibition of whole blood cholinesterase was greater when samples were stored before the assay. Since measurement of cholinesterase activity is not always possible immediately after sampling, the effects of different storage conditions were evaluated. Human blood cholinesterases were inhibited in vitro by methylcarbamates and stored at different pH values, temperatures, and sample dilutions. The results showed that the degree of cholinesterase inhibition does not change if samples are diluted 300-fold with buffer at pH 5.0 at 4 degrees C and the enzyme activity measured within 4 hours after dilution. These conditions of storage were equally satisfactory for each of the three methylcarbamates studied and are therefore likely to apply to other carbamates as well.

Carbamates↗
PubMed1972

Effect of temperature and pH on carbamoylation and phosphorylation of serum cholinesterases. Theoretical interpretation of activation energies in complex reactions.

1. The effect of temperature and pH was studied on the kinetics of inhibition of horse serum and human serum cholinesterase by four organophosphorus compounds and five carbamates. 2. For all compounds, and at each pH and temperature, the inhibition followed the kinetics of a bimolecular reaction with the inhibitor in excess, and with a negligible concentration of the Michaelis complex. 3. The second-order rate constants (k(a)) for inhibition of human serum cholinesterase by one organophosphate and one carbamate increased from 5 degrees to 40 degrees C with an apparent activation energy of 46kJ/mol (11kcal/mol). 4. The k(a) constant for inhibition of horse serum cholinesterase increased with temperature from 5 degrees to 30 degrees C, and then decreased from 30 degrees to 40 degrees C. The theoretical interpretation of such an unusual effect of temperature is derived. 5. The increase of k(a) with pH (human serum cholinesterase) followed the dissociation curve for a single group on the enzyme (pK7.5). 6. Rate constants for decarbamoylation (k(+3)) were determined, and the time-course of inhibition was calculated from the k(a) and k(+3) constants.

Animals↗
PubMed1971

Spontaneous reactivation of phosphorylated and carbamylated cholinesterases.

This paper presents, in tabular form, extensive data on the rates of spontaneous reactivation of phosphorylated and carbamylated cholinesterases from numerous animal species. The half-lives clearly indicate the influence of the acyl group of the inhibitor and that of the source of the enzyme.

Acetylcholinesterase↗
PubMed1969

Acetylcholinesterase. Two types of inhibition by an organophosphorus compound: one the formation of phosphorylated enzyme and the other analogous to inhibition by substrate.

1. The kinetics of the reaction of di-(2-chloroethyl) 3-chloro-4-methylcoumarin-7-yl phosphate (haloxon) and related compounds with acetylcholinesterase were studied and found to be unusual. 2. By a progressive reaction haloxon produces a di-(2-chloroethyl)phosphorylated enzyme. The influence of substrate on this reaction leading to a phosphorylated active centre was studied. From competition experiments between inhibitor and substrate values of K(m) for acetylcholine and acetylthiocholine of 0.79mm and 0.23mm respectively were derived. 3. Haloxon also combines with acetylcholinesterase by a non-progressive reaction, producing a complex that is reversible by dilution and by high concentrations of acetylcholine and acetylthiocholine. From this non-progressive reaction the competition between haloxon and substrate was studied, and it was shown that haloxon combines with a site involved in inhibition by substrate. From competition experiments the following dissociation constants were derived: for combination of haloxon and this site K(i) is 4.9mum and for the combination of substrates with this site K(88) values are 12mm and 3.3mm for acetylcholine and acetylthiocholine respectively. 4. The non-phosphorus-containing compound 3-chloro-7-hydroxy-4-methylcoumarin was shown to be a good reagent for the site involved in inhibition by substrate; its dissociation constant for the combination with this site is 30mum. 5. In order to interpret the experimental results, theoretical equations were derived for an enzyme with two binding sites to both of which substrate and inhibitor can combine. The equations correlate the activity of the enzyme with the concentration of substrate and inhibitor, for both progressive and non-progressive inhibition. These equations are applicable to reactions of acetylcholinesterase with organophosphorus compounds, carbamates etc. and may be applicable to other enzymes possessing two binding sites.

Acetylcholine↗