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 1,405 records · Page 78Linked to original sources
PubMed1997

Carbohydrate induced modulation of cell membrane. VI. Binding of exogenous lectin induces susceptibility of erythrocytes to free radical damage: a spin label study.

The oxidation of erythrocyte membrane has been widely used as a model to study the damage of biomembranes by free radicals. Whether binding of lectin to erythrocytes has any effect on peroxidant injury has never been studied. This study reports for the first time that crosslinking of erythrocyte surface glycoprotein by an exogenous lectin significantly enhances the susceptibility to membrane damage by free radicals, as evidenced by the increase in membrane fluidity measured by EPR using spin label and the increase in the amount of oxyhemoglobin liberated due to cell lysis.

Animals↗
PubMed2002

The membrane-dipped neuronal SNARE complex: a site-directed spin labeling electron paramagnetic resonance study.

The formation of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex is an essential process for membrane fusion and the neurotransmitter release in neurons. As an initial step toward the determination of the membrane topology of the SNARE complex, residues at the membrane-water interface were investigated with site-specific spin labeling electron paramagnetic resonance. EPR analysis revealed that the basic amino acid-rich interfacial region, which is universal for all transmembrane SNARE proteins, inserts into the membrane, eliminating the gap between the core complex and the membrane. The result raises the possibility that core complex formation directly leads to the apposition of two membranes, which could facilitate membrane fusion.

Amino Acid Sequence↗
PubMed2000

"Spin-labelling" with the second hydrogen radioisotope: radicals formed from squalene by muonium addition.

By radio-labelling with muonium (the second hydrogen radioisotope), a free radical species has been clearly identified in squalene (2,6,10,15,19,23-hexamethyl-2,6,10,14,18,22-tetracosahexaene ) with a muon-electron hyperfine coupling of 240.7 MHz, as measured by the muon spin rotation (MuSR) technique. The radical is undetectable in pure squalene due to its high viscosity and the large molecular size which leads to extreme line broadening, but its signals may be resolved on reducing the viscosity of the medium by dilution with diethyl ether. The potential of the MuSR method is thus demonstrated as a means for spin-labelling radical species such as are formed from cellular antioxidants; ESR spectroscopy is unsuitable for studies of radicals formed from this molecule, due to extreme line-broadening and spectral complexity.

Electron Spin Resonance Spectroscopy↗
PubMed1976

Versatility of oxazolidine spin labels--a model study with acyl-alpha-chymotrypsin.

The p-nitrophenyl ester of N-oxyl-4',4'-dimethyl-3-oxazolidinebutyric acid was synthesized. The resonance spectrum of the acyl-alpha-chymotrypsin intermediate of this substrate was found to have more motional freedom at the enzyme active site as compared to the acyl-enzyme prepared from the p-nitrophenyl esters of 1-oxyl-2,2,5,5-tetramethyl-3-carboxypyrrolidine and 1-oxyl-2,2,6,6-tetramethyl-4-carboxy-1,2,5,6-tetrahydropyridine. The flexibility and the versatility of Keana's oxazolidine spin labels as covalent conformational probes is discussed.

Binding Sites↗
PubMed1985

Association of spin-labelled cardiolipin with dimyristoylphosphatidylcholine-substituted bovine heart cytochrome c oxidase. A generalized specificity increase rather than highly specific binding sites.

The endogeneous lipid of bovine heart cytochrome c oxidase has been replaced by dimyristoylphosphatidylcholine using cholate-mediated exchange. The lipid-substituted preparation contained less than 1 mole cardiolipin per mole enzyme and possessed full oxidative activity. The association of spin-labelled cardiolipin with such lipid-substituted cytochrome oxidase preparations has been assayed using ESR spectroscopy. An average relative association constant 5.4-times that for phosphatidylcholine is obtained for cardiolipin. Measurements on preparations with increasing contents of unlabelled cardiolipin, introduced during lipid exchange, reveal that this selectivity corresponds to a generalized increase in specificity for all lipid association sites on the protein.

Animals↗
PubMed1994

Effect of beta-carotene on structural and dynamic properties of model phosphatidylcholine membranes. I. An EPR spin label study.

The influence of beta-carotene on structural and dynamic properties of model membranes (multilamellar liposomes) prepared of dipalmitoylphosphatidylcholine was investigated. It was found that beta-carotene: (1) decreases order within crystalline state of the membrane; the effect of beta-carotene was more pronounced than in the case of the polar carotenoid, lutein, as revealed by means of spin label EPR; (2) increases penetration, stronger than lutein, of apolar molecules into the membrane as indicated by greater partition coefficient of 5-doxyldecane; (3) increases correlation times tau B tau C stronger than lutein. In all cases the effect of beta-carotene on a membrane was more pronounced at crystalline state than at fluid state. On this basis a hypothesis is proposed that beta-carotene plays a physiological function in the fluidization of chloroplast membranes in a chilling stress to the photosynthetic apparatus.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1985

Comparison of the active sites of atropinesterase and some serine proteases by spin-labeling.

The side chain of the serine residue in the active center of atropinesterase (AtrE), alpha-chymotrypsin (Chymo), and subtilisin A (Sub) was labeled with two paramagnetic reporter groups of different size (label I or II, respectively) by sulfonylation with N-[3-(fluorosulfonyl)phenyl]-1-oxy-2,2,5,5-tetramethyl-pyrroline-3 -carboxamide or N-[6-(fluorosulfonyl)-2-naphthyl]-1-oxy-2,2,5,5-tetramethylpyrroline+ ++-3 -carboxamide. ESR spectra of labeled enzymes in 10 mM phosphate buffer, pH 7.4, were measured at temperatures between 133 and 298 K by using a home-built spectrometer operating in the absorption mode at 10-kHz field modulation. The spectra, in particular those at 276-298 K, were analyzed by computer simulation of the overall line shape according to the methods developed by Freed and co-workers, based on eigenfunction expansion. In the case of AtrE for both labels, the best agreement between experimental and simulated solution spectra was obtained with only one mobility component showing anisotropic, axially symmetric reorientation according to the Egelstaff jump-diffusion model. The axis of preferential reorientation was found to lie in the XZ plane at a polar angle of about 30 degrees with the X axis. The corresponding rotational correlation time (tau parallel) did not show appreciable viscosity/temperature (eta/T) dependence but had a constant value of 4.4 and 2.2 ns for labels I and II, respectively. The rotational correlation time associated with rotation around the axes perpendicular to that of preferential reorientation (tau perpendicular) showed the usual eta/T dependence and had a value of 22.0 ns at 276 K for both labels. The above results strongly suggest that in AtrE both nonpolar reporter groups reside in a pocket near the active serine. Contrary to the situation in AtrE, the overall mobility of the -N-O. fragments in Chymo and Sub was found to result from contributions of at least two distinct motional states, strongly and weakly immobilized. In going from label I to label II, the relative contribution of the latter state increases at the expense of that of the former. This is ascribed to an equilibrium between a relatively free state of the aromatic cores and a firmly bound position in the specificity pocket of these proteases. The apparently more rigid embedding of the spin-labels in the enzyme structure of AtrE suggests that the size of the nonpolar binding pocket in the active center region of this esterase allows a deeper penetration of the aromatic portions of the labels than is possible for the specificity pocket of Chymo or Sub.

Binding Sites↗
PubMed2001

Effect of magainin, class L, and class A amphipathic peptides on fatty acid spin labels in lipid bilayers.

Magainins and other antimicrobial peptides increase ion flux across the membrane. They may do this by forming some type of pore or by perturbing lipid organization due to peptide lying on the bilayer surface. In order to determine if magainins perturb the lipid sufficiently to permeabilize the bilayer, their effect on the motion of fatty acid and lipid spin labels in phosphatidylcholine/phosphatidylglycerol (PC/PG) lipid vesicles was determined. Their effect was compared to two synthetic peptides, 18L and Ac-18A-NH(2), designed to mimic the naturally occurring classes of lytic (class L) and apolipoprotein (class A) amphipathic helices, respectively. We show that although magainins and 18L both had significant effects on lipid chain order, much greater than Ac-18A-NH(2), there was no correlation between these effects and the relative ability of these three peptide classes to permeabilize PC/PG vesicles in the order magainins=Ac-18A-NH(2) >> 18L. This suggests that the perturbing effects of magainins on lipid chain order at permeabilizing concentrations are not directly responsible for the increased leakage of vesicle contents. The greater ability of the magainins to permeabilize PC/PG vesicles relative to 18L is thus more likely due to formation of some type of pore by magainins. The greater ability of Ac-18A-NH(2) relative to 18L to permeabilize PC/PG vesicles despite its lack of disordering effect must be due to its ability to cause membrane fragmentation. Effects of these peptides on other lipids indicated that the mechanism by which they permeabilize lipid bilayers depends both on the peptide and on the lipid composition of the vesicles.

Amino Acid Sequence↗
PubMed2005

Murine orthostatic response during prolonged vertical studies: effect on cerebral blood flow measured by arterial spin-labeled MRI.

High-field MRI scanners are, in principle, well suited for mouse studies; however, many high-field magnets employ a vertical design that may influence the physiological state of the rodent. The purpose of this study was to investigate the orthostatic response of cerebral blood flow (CBF) in mice during a prolonged MR experiment in the vertical position. Arterial spin-labeled (ASL) MRI was performed at 4.7-Tesla with a 15-cm gradient insert that allowed horizontal and vertical CBF measurements to be obtained with the same scanner. For mice in the head-up (HU) vertical position, CBF decreased by approximately 40% compared to the horizontal position, although blood pressure did not differ. Furthermore, CBF values for vertically positioned mice treated with phenylephrine remained constant while blood pressure increased. These results support the conclusion that cerebral autoregulation was intact, albeit at a lower level. Since CBF recovers to near horizontal values by volume loading with saline, it appears that a decrease in central venous pressure (CVP) leading to an increase in sympathetic tone may be a contributing mechanism for lowered CBF. This suggests that using an HU vertical position for MRI in mice may have broader implications, especially for studies that rely on CBF (such as BOLD and fMRI).

Adaptation, Physiological↗
PubMed1990

Effect of high electrolyte concentration on the phase transition behaviour of DPPC vesicles: a spin label study.

We have investigated by Electron Spin Resonance spectroscopy, the effects of high electrolyte concentration on the phase transitions of unilamellar vesicles of dipalmitoylphosphatidylcholine at the pH values of 5.0 and 9.0. Using the 5-nitroxide stearic acid as spin probe we have found that, at both pH values, the lipid main phase transition is not quite affected by variations of the electrolyte concentration up to the value of 3 M. Instead, the pretransition at pH 5.0 disappears in the presence of 1 M electrolyte, and at pH 9.0, the pretransition temperature shifts upward from 25.5 to 31.0 degrees C when the electrolyte concentration reaches the value of 3 M. The observed results on the pre- and main phase transition widths, transition temperatures and their cooperativity indicate that the presence of salt in the bulk solution leads to structural changes of the lipid bilayer which essentially concern either the polar zone or the hydrogen belt region of the DPPC vesicles. The extent of observed perturbation depends on salt concentration.

1,2-Dipalmitoylphosphatidylcholine↗
PubMedDate not supplied

[Using the spin label and probe method in medical research].

Spin probe methods applied in membrane medical research are reviewed. The results of erythrocyte membrane studies in diabetes demonstrate potentialities of the methods in medical investigations. The new data on the changes occurring in the erythrocyte membranes of patients suffering from type I diabetes are under discussion.

Diabetes Mellitus, Type 1↗
PubMed1975

A comparison of a spin-label and a fluorescent cell membrane probe using pure and mixed monomolecular films.

Monocular films studies of 12-nitroxide stearic acid and 12-(9-anthroyl) stearic acid reveal that deviations from the behavior of the parent molecule (stearic acid) are as much dictated by the polar, or nonpolar, nature of the probe group as by its size. In mixed films under membrane-like conditions, the spin label probe, 12-nitroxide stearic acid, exhibits positive deviations from ideality and should read too high a fluidity. The picture is, however, complicated by a tendency of this probe molecule to adopt a bent conformation, a tendency apparently enhanced by specific interactions with the lecithin zwitterion. 12-(9-anthroyl) stearic acid, in contrast, shows only negative deviations from ideality in mixed dipalmitoyl lecithin films and should read too low a fluidity.

Anthracenes↗
PubMed2004

Conformation-dependent interaction of alpha-lactalbumin with model and biological membranes: a spin-label ESR study.

Alpha-lactalbumin (alpha-LA) is biosynthesized and stored at the smooth endoplasmic reticulum (ER), then transferred to the Golgi lumen when prolactin stimulation of lactose biosynthesis and secretion takes place. Because both environments are composed of membranes, it was of interest to examine the interactions of alpha-LA with relevant model and biological membranes. Using the ESR spin-labeled fatty acid analog 5-doxyl stearic acid, we found evidence reflecting the insertion of "acid-shocked" molten globule (MG) alpha-LA into lecithin or phosphatidylserine (PS) multi-lamellar vesicles. An additional approximately 3 G immobilization was observed in the alpha-LA-lecithin sample versus the lipid alone. With PS, the increased immobilization was almost 6 G, reflecting an enhanced effect caused by strong electrostatic interactions between the positively charged protein with the negatively charged headgroup at pH 2.4. This was also reflected in the broadening of the PS:alpha-LA phase transition. Additionally, we have demonstrated that alpha-LA in its apo-form also shows similar insertion characteristics with both model and natural lipid membranes. Upon addition of calcium, the apo-form is released from the membrane as the Ca(2+)-bound protein.

Animals↗
PubMed2001

Site-directed spin-labeling analysis of reconstituted Mscl in the closed state.

The mechanosensitive channel from Escherichia coli (Eco-MscL) responds to membrane lateral tension by opening a large, water-filled pore that serves as an osmotic safety valve. In an attempt to understand the structural dynamics of MscL in the closed state and under physiological conditions, we have performed a systematic site-directed spin labeling study of this channel reconstituted in a membrane bilayer. Structural information was derived from an analysis of probe mobility, residue accessibility to O(2) or NiEdda and overall intersubunit proximity. For the majority of the residues studied, mobility and accessibility data showed a remarkable agreement with the Mycobacterium tuberculosis crystal structure, clearly identifying residues facing the large water-filled vestibule at the extracellular face of the molecule, the narrowest point along the permeation pathway (residues 21-26 of Eco-MscL), and the lipid-exposed residues in the peripheral transmembrane segments (TM2). Overall, the present dataset demonstrates that the transmembrane regions of the MscL crystal structure (obtained in detergent and at low pH) are, in general, an accurate representation of its structure in a membrane bilayer under physiological conditions. However, significant differences between the EPR data and the crystal structure were found toward the COOH-terminal end of TM2.

Amino Acid Sequence↗
PubMed1991

ESR spectra reflect local and global mobility in a short spin-labeled peptide throughout the alpha-helix----coil transition.

A series of short alanine-based synthetic peptides (16 or 17 residues) have previously been shown to exhibit an anomalously high degree of alpha-helicity [Marqusee, S., et al. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 5286-5290; Marqusee, S., & Baldwin, R.L. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 8898-8902]. These peptides are ideal models for extracting position-dependent structural and dynamic information. Using the methanethiosulfonate nitroxide spin label (MTSSL), we labeled an analogue of the salt-bridge-stabilized "i+4" peptide, called the "i+4c", which has a specific attachment site created by replacing the central alanine with a cysteine. Circular dichroism (CD) spectra demonstrate that the i+4c-MTSSL peptide retains nearly the same helicity as the original i+4 peptide. The ESR spectra of the labeled peptide indicate no significant aggregation. ESR spectra were acquired throughout the helix-coil transition by temperature variation. From the motionally narrowed spectra, we extracted the rotational correlation times of the nitroxide label. Parallel measurements with circular dichroism enabled us to relate these parameters directly to the fractional helicity. For comparison, we followed a similar procedure with MTSSL-labeled glutathione (GS-MTSSL), a tripeptide that does not form an alpha-helix. Our results are interpreted in terms of a local tumbling volume, V(L), which reflects the portion of the peptide that reorients with the nitroxide label. At high fractional helicity, V(L) is similar to the volume expected for a 17-residue helix.

Amino Acid Sequence↗
PubMed1977

Electron spin resonance studies on the lipoxygenase reaction by spin trapping and spin labelling methods.

The rate of oxygenation and that of trapping linoleic acid free radicals in the lipoxygenase [EC 1.13.11.12] reaction were measured in the presence of linoleic acid, oxygen, and nitrosobenzene at various concentrations, with a Clark oxygen electrode and ESR spectroscopy. The results were interpreted under the assumption that the free radical of linoleic acid, an intermediate of the lipoxygenase reaction, reacts competitively with oxygen or nitrosobenzene. The oxidation of the iron in the active site of lipoxygenase caused by the spin label reagent, 2-(10-carboxydecyl)-2-hexyl-4,4-dimethyl-3-oxazolidinyloxyl, was also observed by ESR- and fluorescence-spectroscopy.

Electron Spin Resonance Spectroscopy↗
PubMed1994

Tissue specific perfusion imaging using arterial spin labeling.

Quantitative magnetic resonance measurements of regional tissue perfusion can be obtained using magnetically labeled arterial water as a diffusable tracer. Continuous labeling is achieved in flowing spins using adiabatic inversion. The effects of continuous labeling of proximal arterial spins and T1 relaxation in distal tissue magnetization result in a steady-state change in tissue magnetization which is tissue specific, i.e., it can be quantified in units of blood flow per gram of tissue per unit time. This magnetization is sampled using standard imaging sequences. The theoretical basis for this method, including the effects of macromolecular spin saturation, is reviewed. Recent results demonstrating the successful implementation of this technique in vitro and in vivo in rat brain, heart, and kidney, and in human brain and kidney are presented, as well as the use of a separate RF coil for arterial labeling to produce selective perfusion images in rat brain. This approach allows quantitative perfusion images to be obtained completely non-invasively at the resolution of 1H MRI, and is useful in the clinical and investigational evaluation of organ physiology.

Animals↗
PubMed1975

Rotational correlation times and partition coefficients of a spin label solute in lecithin vesicles.

Di-tert-butylnitroxide dissolved in an aqueous suspension of egg yolk lecithin vesicles is distributed between the two phases. Partition coefficients of the nitroxide between the lipid and the water, calculated from the nitroxide electron paramagnetic resonance (EPR) spectra, decrease with decreasing temperature until approximately the freezing point of the solvent. Below this temperature the nitroxide is detected only in the lecithin. The rotational correlation times of the spin label present in the lecithin were calculated for the temperature range from +45 to -60 degrees C. At low temperatures, the EPR spectra are characteristic of a superposition of two spectra resulting from the nitroxide dissolved in the lipid in two environments with different rotational correlation times.

Electron Spin Resonance Spectroscopy↗