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D L Rabenstein

Publications and source records attributed to D L Rabenstein.

At least 55 records · Page 3Linked to original sources
PubMed1982

A proton nuclear magnetic resonance study of the interaction of mercury with intact human erythrocytes.

The binding of mercuric ion (Hg(II)) by small molecules in the intracellular region of intact human erythrocytes has been studied by 1H-NMR spectroscopy. HgCl2 added to intact erythrocytes in saline-glucose suspension is found to cross the membrane and reach an equilibrium distribution among the molecules of the erythrocyte within 4 min. In the intracellular region Hg(II) reacts with GSH and hemoglobin to form the ternary mixed-ligand complex GSH-Hg(II)-hemoglobin. The analogous complex with ergothioneine is formed after all the GSH is complexed. 1H-NMR spectra show that the GSH-Hg(II)-hemoglobin complex also forms in simpler solutions containing HgCl2, GSH and hemoglobin, whereas the complex Hg(GSH)2 predominates in solutions of GSH and HgCl2. The lifetime of the GSH in the GSH-Hg(II)-hemoglobin complex is shown to be less than 30 s, which provides direct evidence for the first time that Hg(II) complexes in biological systems are quite labile, even though their thermodynamic stability is large. The effectiveness of eight sulfhydryl-containing ligands, some of which have been used as antidotes for Hg(II) poisoning, for releasing GSH from its Hg(II) complex in hemolyzed erythrocytes was also studied. Dithiol ligands were found to be more effective than monothiols, with dithioerythritol the most effective of the dithiols.

Antidotes↗
PubMed1982

A proton nuclear magnetic resonance study of the binding of methylmercury in human erythrocytes.

The binding of methylmercury, CH3Hg(II), by small molecules in the intracellular region of human erythrocytes has been studied by 1H-NMR spectroscopy. To suppress or completely eliminate interfering resonances from the much more abundant hemoglobin protons, spectra were measured by a technique based on the transfer of saturation throughout the envelope of hemoglobin resonances following a selective presaturation pulse or by the spin-echo Fourier transform method. With these techniques, 1H-NMR spectra were measured for the more abundant intracellular small molecules, including glycine, alanine, creatine, lactic acid, ergothioneine and glutathione, both intact and hemolyzed erythrocytes to which CH3Hg(II) had been added. The results for intact erythrocytes indicate that part of the CH3Hg(II) is complexed by intracellular glutathione. These results also indicate that exchange of CH3Hg(II) among glutathione molecules is fast, with the average lifetime of a CH3Hg(II)-glutathione complex estimated to be less than 0.01 s. From exchange-averaged chemical shifts of the resonance for the proton on the alpha-carbon of the cysteine residue of glutathione, it is shown that, in hemolyzed erythrocytes, the sulfhydryl group of glutathione binds CH3Hg(II) more strongly than the sulfhydryl groups of hemoglobin.

Erythrocytes↗
PubMed1979

Proton magnetic resonance studies on [methionine]-enkephalin and beta-endorphin in aqueous solution.

Proton magnetic resonance studies of [Met5]-enkephalin (lipotropin 61-65) in aqueous solution indicate a conformational preference for the pentapeptide backbone. The structural differences between [Met5]-enkephalin and other, more flexible peptides have been investigated using paramagnetic probe techniques. An outline structure for beta-endorphin (lipotropin 61-91) in aqueous solution is obtained from binding studies using Gd(III) as a relaxation probe.

Animals↗
PubMed1978

The mobility of methylmercury in biological systems.

Toxicology studies indicate that methylmercury in humans and other species is bonded to sulfhydryl ligands and that the methylmercury in such complexes is labile even though their thermodynamic stability is large. It is shown in this paper that bimolecular nucleophilic displacement of complexed ligand by sulfhydryl-deprotonated ligand is the major pathway for ligand exchange at physiological pH, while at the pH of the stomach the proton-assisted dissociation of the complex is the predominant means by which exchange occurs. The dynamic and equilibrium aspects of the distribution of methylmercury between chloride and sulfhydryl ligands under the solution conditions of the stomach are also considered with respect to a possible role for lipid-soluble CH3HgCl in the absorption of methylmercury from the stomach.

Cysteine↗
PubMed1978

Analysis for glutathione in blood by high-performance liquid chromatography.

A high-performance liquid chromatographic method is presented for determination of glutathione in whole blood. Sample preparation involves hemolysis, protein precipitation, centrifugation, and filtration. The glutathione in the filtrate is then separated from other sulfhydryl-containing molecules by liquid chromatography with Zipax SCX cation-exchanger followed by detection with a mercury-based electrochemical detector. The liquid-chromatographic analysis time is approximately 5 min. Because of the chromatographic separation and the selectivity of the detector, the detection step is free from interferences from other components of blood. The method has been checked by comparison with the colorimetric assay based on reaction with 5,5'-dithiobis(2-nitrobenzoic acid). The chromatographic results are consistently slightly lower, presumably because of the greater selectivity of this method.

Chromatography, High Pressure Liquid↗
PubMed1977

Determination of the microscopic and macroscopic acid dissociation constants of glycyl-L-histidyl-L-lysine and related histidine peptides.

Proton magnetic resonance studies of the acid-base chemistry of the glycyl ammonium, histidyl imidazolium, and lysyl ammonium groups of glycyl-L-histidyl-L-lysine and of the glycyl ammonium and histidyl imidazolium groups of glycyl-L-histidine and glycyl-L-histidylglycine are described. Chemical-shift data indicate that, at the molecular level, the glycyl ammonium and the histidyl imidazolium groups are titrated over the same pH range, with the acidity of the imidazolium group some 8 to 10 times that of the glycyl ammonium group, depending on the peptide. The lysyl ammonium group of Gly-His-Lys is much less acidic and is titrated over a higher pH range. Microscopic and macroscopic acid-dissociation constants were determined from chemical-shift data for each of the peptides. It is shown how microscopic formation constants for protonated metal complexes of these ligands, which are being used increasingly as models for the binding of metal ions by proteins, can be calculated from the macroscopic formation constants and the microscopic acid-dissociation constants. The acid-base chemistry of Gly-His-Lys is discussed with respect to its recently discovered biological activity.

Glycine↗
PubMedDate not supplied

1H-NMR study of the removal of methylmercury from intact erythrocytes by sulfhydryl compounds.

The effectiveness of penicillamine, N-acetylpenicillamine, meso-2,3-dimercaptosuccinic acid, 2,3-dimercaptopropanesulfonic acid, and dithioerythritol for removing methylmercury (CH3Hg(II) from intact human erythrocytes has been studied by 1H-nuclear magnetic resonance spectroscopy. The removal of CH3Hg(II) was monitored by measuring the chemical shift of the resonance for the proton on the alpha-carbon of the cysteinyl residue of intracellular glutathione in 1H-NMR spectra of intact, CH3Hg(II)-containing erythrocytes in suspensions to which the sulfhydryl ligands were added. Because exchange of intracellular glutathione between its free and CH3Hg(II) complexed forms is fast, the chemical shift of the cysteinyl resonance provides a direct, noninvasive measure of the fraction of intracellular glutathione that is complexed. The sulfhydryl ligands were found to remove CH3Hg(II) from intact erythrocytes in the order 2,3-dimercaptosuccinic acid greater than 2,3-dimercaptopropane sulfonic acid greater than dithioerythritol greater than penicillamine approximately N-acetylpenicillamine, which also is the order of the conditional formation constants of the CH3Hg(II) complexes at pH 7.4. All five ligands removed CH3Hg(II) from intact erythrocytes much more rapidly than can be accounted for by a mechanism in which the ligand crosses the membrane, combines with the CH3Hg(II), and then transports it out of the cell. An alternative mechanism is proposed in which the ligand reacts with CH3Hg(II) which is complexed by sulfhydryl groups of the membrane, which in turn react with the intracellular CH3Hg(II) to bring more CH3Hg(II) into the membrane, where it can react with the added sulfhydryl ligand.

Erythrocytes↗