Reaction Of N-ethylmaleimide Research Articles

Radical reactions of N-ethyl maleimide in radiation sensitization.

Radical reactions of N-ethyl maleimide in radiation sensitization.

Preparation and properties of smooth muscle myosin from horse esophagus

Myosin was prepared from smooth muscle of horse esophagus in good yield (about 150 mg/100 g tissue) and was designated myosin S. Its properties were compared with those of myosin A from skeletal muscle. The ratio of the absorption of myosin S at 280 nm to that at 260 nm was about 1.8, and the amount of contaminating phosphorus was only 0.91 g/10 5 g of myosin S, indicating that the latter is free of nucleic acid. The purity of this protein was examined by ultracentrifugation, gel filtration in the presence of 0.5 M KCl and 6 M urea and chromatography on DEAE-cellulose columns. These experiments all indicated that myosin S was homogeneous, like highly purified rabbit skeletal myosin A. Amino acid analyses showed differences in the composition of smooth and skeletal myosins. Myosin S contained the same amount of sulfhydryl groups per 10 5 g of protein as horse and rabbit skeletal myosin A (about 8 moles/10 5 g of protein). But it contained more asparatic acid or asparagine, more leucine and less lysine, glycine and proline. Ca 2+-ATPase of myosin S in the presence of 0.5 M KCl and Mg 2+-ATPase in the presence of 0.05 M KCl at 37° were very similar to those of skeletal myosin A. On the other hand, EDTA-ATPase and Ca 2+-ATPase in the presence of 0.05 M KCl were much lower than those of skeletal myosin A. Lowering the temperature from 37 to 25°, the degree of decrease of the ATPase activities was much larger in myosin S than in skeletal myosin A. The reaction of N-ethylmaleimide with myosin S caused inhibition of the EDTA-ATPase but did not affect the Ca 2+-ATPase activity. This behaviour was different from that of skeletal myosin A which exhibited an inhibition of EDTA-ATPase and an activation of Ca 2+-ATPase during the course of the reaction of sulfhydryl groups of myosin with N-ethylmaleimide. These facts suggest that the structure of the active site of myosin S ATPase differs significantly from that of skeletal myosin A. These differences appear to influence the interaction of myosin with F-actin, so that the rate of superprecipitation found in an actomyosin reconstituted from myosin S and F-actin was only one fortieth of that found with skeletal myosin A.

The radiosensitization of Micrococcus sodonensis by N-ethyl maleimide.

SummaryRadiosensitization of the bacterium Micrococcus sodonensis by N-ethyl maleimide (NEM) has been obtained by administering the sensitizer before, during, and after irradiation. It has been shown that there are three different mechanisms of sensitization by NEM:(i) caused by an intracellular reaction, presumably with sulphydryl groups,(ii) caused by the reaction of NEM with a reducing species, probably with the electron, to give a short-lived toxic product, and(iii) caused by interference with the post-irradiation repair processes.The experiments also indicate that NEM is able to penetrate the cell while another sulphydryl poison, iodoacetamide, cannot. This accounts for some of the difference in the mode of action of these two radiosensitizers.

Acylation reactions with cyclic imides

Maleimide reagents have been examined for a potential use in the cross-linking of amino and thiol groups in proteins. The adducts obtained by reaction of N-ethylmaleimide or of N-(4-dimethyl-3,5-dinitroaminophenyl)maleimide with cysteine, homocysteine, and glutathione were prepared and the rates of reaction of the imide rings with water and with amino groups were studied. In the cysteine—maleimide addition products, where amino and thiol groups are located in positions sterically favourable for cross-linking, intramolecular aminolysis occurs readily. In contrast, the amino group of the homocysteine and glutathione adducts is comparatively stable.

Inactivation of yeast alcohol dehydrogenase by N-alkylmaleimides

Seven N-alkylmaleamic acids were synthesized and converted through heating to the corresponding N-alkylmaleimides. Alkylmaleimides of varying chainlength were shown to effectively inactivate yeast alcohol dehydrogenase at pH 7.0. The effect of pH on the rate of hydrolysis of N-ethylmaleimide was studied in the pH range from 8.6 to 9.4 where specific base catalysis of the reaction was observed. Second-order rate constants for maleimide inactivation of yeast alcohol dehydrogenase were shown to increase with increasing chainlength of the alkyl substituents of the maleimide derivatives. A chainlength effect was not observed in the reaction of N-ethylmaleimide and N-heptylmaleimide with cysteine and glutathione. Yeast glucose 6-phosphate dehydrogenase, which is less sensitive to maleimide inactivation than is yeast alcohol dehydrogenase, was inactivated by both N-ethyl and N-heptylmaleimide at rates indicating no appreciable chainlength effect.

Spectral shifts in the reaction of N-ethylmaleimide with proteins

Spectral shifts in the reaction of N-ethylmaleimide with proteins

Some Reactions of N-Ethylmaleimide1

Some Reactions of N-Ethylmaleimide¹