Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Spin Labels”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources
PubMed1977

Spin label studies on the human erythrocyte membrane. Two sites and two phases for fatty acid spin labels.

Human erythrocytes, untreated and glutaraldehyde-treated, were spin labeled with three kinds of fatty acid labels, and their electron spin resonance (ESR) spectra were studied in detail at various temperatures. 1. The better spectral resolution could be obtained by packing the erythrocytes in a hematocrit capillary tube, because of the preferential parallel orientation of the cylindrical axes of erythrocyte-disc to the centrifugal axis. 2. It was demonstrated by the incorporation and the release of the labels that the membrane possessed two kinds of the fatty acid "sites": the tightly and weakly binding "sites" at the approximate molar ratio of 1:1. The rough estimates of the binding constants were obtained, which reproducibly varied with the blood donors over a period of a year. 3. The temperature dependency of the ESR spectra revealed the presence of two distinct phases, perhaps the solid and fluid phases. With lowering of the temperature, the fluid phase became more solid but the solid phase unchanged. The pretreatment of the erythrocytes with glutaraldehyde increased the amount of the frozen phase, corresponding to the decrease of the membrane flexibility.

Albumins↗
PubMed1996

Effects of fumonisin B1 and (hydrolyzed) fumonisin backbone AP1 on membranes: a spin-label study.

Electron spin resonance (ESR) spectroscopy and spin label techniques have been used to study the effects of fumonisin B1 (FB1) and hydrolyzed fumonisin backbone (AP1) on the structural and dynamic properties of phosphatidylcholine membranes at the molecular level. Multilamellar liposomes consisting of dimyristoylphosphatidylcholine (DMPC) and egg yolk phosphatidylcholine (EYPC) were used. Six different nitroxide spin labels were used to determine what effects FB1 may impart on the ordering and mobility of lipids in membranes. The experimental results disclose the following: (1) In the fluid phase membrane, FB1 significantly increases the fluidities of n-doxylstearic acid (SA) spin labels (SL) attached to carbons 5 and 7, which disorders the alkyl chains and perturbs the surface region of the bilayer; by comparison, minimal effects were detected near the center of the bilayer. (2) In the gel phase, FB1 and AP1 imparts marked rigidifying effects on membrane fluidity, which enlarges the change in ordering on the phase transition even further. (3) FB1 also restricts the mobility of the (rigid) cholestane spin label. (4) A reduction in mobility of the tempo-stearate spin label suggests that the tricarballylic acid (TCA) moieties of FB1 might mimic the structure of polar headgroups in phospholipids. The present results may provide additional mechanisms to elucidate the toxicological activities of the fumonisins.

Dimyristoylphosphatidylcholine↗
PubMed1984

Association-dissociation of histone oligomers. A spin label study.

The spin label method has been used to obtain information about conformational changes of histone oligomers taking advantage of the fact that at a low ionic strength and in the presence of other histones about 45% of cysteine residues of histone H3 react with the 3-maleimido-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl spin label. For the labeled complexes H3-H4 and H nu the degree of immobilization of the spin label is a function of the ionic strength. This variation is identical for both complexes within a long range of ionic strengths, including the interval of 0.8-2 M NaCl, under which conditions interactions are known to exist between the tetramer (H3)2 (H4)2 and the dimer (H2A) (H2B). This finding suggests a negligible influence of the dimer for modifying the cysteine residue environment of histone H3 on octamer formation. GuHCl treatment at high ionic strength of the labeled complexes gives rise to a non-lineal increase in the degree of mobility of the spin label. This increase, at low GuHCl concentration (0-0.5 M GuHCl), is interpreted as showing a lowering in rigidity for the Cys residue environment, without affecting the general stability of the tetramer (H3)2 (H4)2. At higher GuHCl concentration (2-3 M GuHCl) the increase in the spin label mobility is related to a dissociation of the complexes in single histones. Our results are consistent with the view that the overall structure of the tetramer, as well as its conformational changes during complex structuration or denaturation, are not strongly affected by the presence of the dimer (H2A) (H2B).

Cysteine↗
PubMedDate not supplied

[Measurements of the time of rotational correlation of bovine serum albumin molecule using iodine and mercury-containing spin-labels].

New spin-labels based on iodine and hydrargirum containing imidazolids were approbated on the bovine serum albumin (BSA) molecule. It is shown that all hydrargirum labels are binded to the external SH-group of BSA practically immediately in comparison with earlier known spin-labels based on piperidine with maleimide and iodacetamide groups, requiring some minutes of hours, correspondingly. Rotational correlation times and the character of relative mobility of the spin-label were measured. Values of the rotational correlation times of the protein molecule obtained by hydrargirum containing labels were found in the range of correlation times typical for the BSA molecule and represent at pH 7.0 a rigid stretch ellipsoid of rotation. The result obtained revealed that the relative reorientation nature of spin-labels is essentially different and is taken into account in different values of order parametres S according to model--fast anisotropic rotator on slow isotropic rotator. ESR spectra based on theoretical calculations by means of computer are given.

Computer Simulation↗
PubMed1988

Methionine-90-spin-labeled bovine alpha-lactalbumin: electron spin resonance and NMR distance measurements.

The unique methionine residue of bovine alpha-lactalbumin was modified by irreversible alkylation with the bromoacetamido nitroxide spin-label 4-(2-bromoacetamido)-2,2,6,6-tetramethylpiperidine-N-oxyl. The line shape of the electron spin resonance (ESR) spectrum was indicative of a fairly mobile spin-label and was sensitive to the calcium-induced conformational change. Paramagnetic broadening of the spin-label ESR lines by a Gd(III) ion substituted at the high-affinity calcium site of the protein yielded a distance between the spin-label and the metal-binding site of 8.0 +/- 1.0 A. The extent of the paramagnetic line broadening by the covalently attached nitroxide spin-label on the proton resonances of several amino acid residues of the protein at 500 MHz allowed estimation of intramolecular distances between the methionine-90 residue and several resolvable protons.

Animals↗
PubMed1992

Spin-labeled phorbol esters and their interactions with cellular membranes--V. Electron paramagnetic resonance of spin-labeled phorbol-12,13-diesters bound to their receptors in mouse brain particulate fraction.

The relatively small concentrations required for in vivo bioactivity of diterpene ester skin irritants and promoters (approximately 10 nmol per animal; approximately 10 nM in cell cultures) has discouraged studies of EPR spectra of bioactive, TPA-analogous, spin-labeled phorbol-12,13-diesters [(n,m)PA] bound to their membrane receptors, protein kinases C (PKC). To meet the requirements of present EPR spectrometers, particulate fraction from mouse brain containing at least 25 x 10(-12) mol of receptors/mg protein (PKC species) were employed together with certain (n,m)PA selected to give an optimal ratio of specific to non-specific binding. For selection and optimization of experimental conditions, a theoretical model was developed that considers all characteristic parameters of the system. By fitting the model calculations to the experimental data of competitive agonist displacement from the particulate fraction of tritium-labeled TPA, the dissociation constants Kd for four selected (n,m)PA used as antagonists were determined. Optimal experimental conditions are met by (5,6)PA and by (5,8)PA, in that for both compounds the relative amount of displaced (n,m)PA is in accordance with the predictions derived from the model. Moreover, the model turned out also to be reliable for samples containing either small or large amounts of membranes. To obtain an EPR spectrum of an agonist bound to brain particulate fraction, the (5,6)PA was used. It shows a broad EPR spectrum typical for an immobilized molecule. The spectrum changes if an excess of TPA is added to the system; the slight differences in shape are due to displacement of (5,6)PA from specific receptor sites by non-labeled TPA and show up as a decreased central peak amplitude. This is the first time that the agonist/receptor interaction of a diterpene ester type irritant and tumor promoter has been demonstrated by direct spectroscopic measurement.

Animals↗
PubMed1980

Bacteriorhodopsin, boundary lipid and protein conformers: a spin label study.

A spin label study, as a function of temperature, has been made with the bacteriorhodopsin membrane using a stearic acid spin label. The ESR spectra show a strong variation with temperature and the presence of isosbestic points. The spectra are interpreted as indicating the presence of a two-component system with an activation energy (approx. 14 kcal/mol) corresponding to a protein conformational change. This activation energy is similar to that deduced from recent flash photolysis studies. It is concluded that the spin label is sensitive to the temperature-dependent protein conformational change in this membrane system.

Bacterial Proteins↗
PubMed1992

Spin-labeled phorbol esters and their interactions with cellular membranes--IV. Lipophilic binding and molecular orientation of spin-labeled phorbol-12,13-diesters in human erythrocyte membrane.

In human erythrocyte membranes, membrane binding of spin-labeled TPA-analogous phorbol (doxyl)esters [(n,m)PA] was investigated during measurement of the kinetics of the decay of their electron paramagnetic resonance signal by ascorbate reduction. In membrane-bound (n,m)PA the reduction rate was dependent of the position of doxyl in the aliphatic chain of their 12-O-acyl moiety. To describe quantitatively the reaction kinetics observed, two hypotheses (models) were developed and used. Model 1 is based on the assumption that ascorbate reduction takes place in the extracellular space. In this case the experimental data could be fitted by the partition and permeability coefficients of (n,m)PA determining model 1 only, if non-realistic values of these parameters were used. The more refined model 2, corresponding to a bilayer membrane structure, assumes the reduction to take place in the hydrophilic region of the membrane. Assuming a finite probability of finding the doxyl group within the hydrophilic membrane region, model 2 describes quantitatively the dependence of the reduction rate on the position of the doxyl in the aliphatic chain of the (n,m)PA used. From the validity of this model it may be postulated that the molecular orientation of TPA-analogous (n,m)PA in the bilayer membrane is determined by an anchoring of their lipophilic ester moiety in the lipophilic region of the membrane bilayer, thus locating the hydrophilic phorbol moiety within the hydrophilic region of the membrane. With regard to the well-known categories of non-specific versus specific binding of bioactive phorbol esters to protein kinase C/membrane complexes it is deduced that anchoring of (n,m)PA (and hence TPA) in the hydrophobic interior of the membrane structure may be the molecular equivalent of their non-specific binding.

Ascorbic Acid↗
PubMed1987

Probing of sulfhydryl groups in the adenosine 5'-diphosphate/adenosine 5'-triphosphate carrier by maleimide spin-labels.

Binding of spin-labeled maleimides to the mitochondrial ADP/ATP carrier was investigated both in mitochondria and in the detergent-solubilized carrier protein. In mitochondria, spin-label binding to the carrier was evaluated by preincubation with the inhibitor carboxyatractyloside. The membrane sidedness of SH groups in the carrier molecule was determined by chemical reduction of nitroxides on the cytosolic membrane surface by Fe2+ or by pretreatment of the mitochondria with impermeant SH reagents. These experiments suggest that each subunit of the dimeric carrier incorporates one spin-labeled maleimide. Roughly half of the carrier-bound spin-labels were found on either side of the mitochondrial membrane. The detergent-solubilized carrier protein was labeled with a series of maleimide derivatives containing a spacer of increasing length between the maleimide and nitroxide moieties. A total spin-label binding of 2-3 mol/mol of protein dimer, depending on the spin-label length, was found. The electron spin resonance spectra of the spin-labeled protein invariably showed strongly and weakly immobilized components. Increasing the distance of the nitroxide from the maleimide ring resulted in a strong increase of the contribution of the weakly immobilized component. These observations led to the conclusions that the geometrical constraint of spin-label mobility changes at a distance of about 10 A from the maleimide binding site.

Animals↗
PubMed1985

Probing the topography of lectins with site-specific spin-labeled glycosides.

Three new spin-labeled glycosides, spin-label I [1-[4-(beta-D-galactopyranosyloxy)phenyl]-3-(2,2,6,6-tetramethyl-1 -oxypiperidin-4-yl)-2-thiourea], spin-label II (2,2,6,6-tetramethyl-1-oxypiperidin-4-yl alpha-D-galactopyranoside), and spin-label III [1-(methyl 2-deoxy-alpha-D-galactopyranosid-2-yl)-3-(2,2,6,6- tetramethyl-1-oxypiperidin-4-yl)-2-thiourea], were investigated as structural probes of Griffonia simplicifolia I isolectins (GS I) A4 and B4, respectively, by electron spin resonance (ESR) and inhibition of guaran isolectin precipitation. The p-aminophenyl beta-galactoside spin-label I was strongly immobilized by the B4 isolectin (Kd = 0.42 mM; 2T parallel = 54.0 +/- 0.3 G), while binding to the A4 isolectin was so weak (KI congruent to 2 mM) that binding was undetectable by ESR. The preference for the B4 isolectin was indicative of a more extended hydrophobic binding locus adjacent to the carbohydrate-specific binding site. The alpha-galactosyl spin-label II bound slightly more strongly to the A4 than to the B4 isolectin, as evidenced in both Kd values and particularly by differences in the degree of immobilization (2T parallel = 53.5 vs. 51.5 G, respectively). The 2-N-substituted methyl galactoside spin-label III was so poor an inhibitor of both isolectins (KI congruent to 1-2 mM) that ESR detection of the bound complex was not feasible. In all cases above, the spin-labels were displaced by specific monosaccharide haptens.

Electron Spin Resonance Spectroscopy↗
PubMed1986

Human erythrocyte membrane permeability and nitroxyl spin-label reduction.

Nitroxyl spin labels are paramagnetic compounds that have demonstrated utility as contrast enhancing agents in proton magnetic resonance imaging. The time-course of contrast enhancement depends on distribution and elimination of these agents. Reduction, resulting in formation of the diamagnetic hydroxylamine, is the major metabolic pathway observed in vivo. This bioreduction has implications for the design of contrast agents and for understanding their imaging behavior. Bioreduction has been shown to occur, at least in part, intracellularly. As such, cell membrane permeability to nitroxyl spin labels may influence their bioreduction. In this study, this influence was examined using eight nitroxyl derivatives and the human erythrocyte suspension as a model biomembrane system. Ionizable weak acids and bases were found to equilibrate rapidly across the erythrocyte membrane with half-times of equilibration ranging from less than 10 s to 1.6 min. These derivatives had low octanol:buffer distribution coefficients and were extensively ionized at the pH of the system (7.0). A strong acid, a phosphate ester, and a quaternary amine derivative were excluded by the cell membrane. Reduction of nitroxyl spin labels by the erythrocyte was shown to occur intracellularly. Except for the impermeable probes, the reduction rate was slow in comparison with the membrane penetration rate. The structural dependence of reduction rate was unrelated to penetration rate but correlated well with that observed in other reducing systems, namely, ascorbic acid solution and rat tissue homogenates.

Buffers↗