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At least 1,207 records · Page 67Linked to original sources
PubMed1994

Molecular dynamics in liquids: spin-lattice relaxation of nitroxide spin labels.

Time domain pulsed saturation recovery and electron-electron double resonance spectroscopies were used to measure the spin-lattice relaxation rates of the electron and the nitrogen nucleus in nitroxide spin labels in liquids. The rotational correlation time range covered is from picoseconds to milliseconds. These rates are quantitatively explained by isotropic rotational Brownian dynamics, which modulate the interactions between the electron spin and the molecular angular momentum; the nitrogen and electron spins; and the solvent protons with both the electron and the nitrogen spins. This solves a 20-year-old problem that has limited scientific applications of nitroxides.

Cyclic N-Oxides↗
PubMed2005

Continuous arterial spin labeling at the human common carotid artery: the influence of transit times.

In evaluating the sensitivity of arterial spin labeling (CASL) and for quantification of perfusion, knowledge of the transit time from the labeling plane to the imaging slice is crucial. The purpose of the current study was to obtain estimates of transit times relevant under the specific experimental conditions of CASL in human subjects using a separate local labeling coil at the neck. Specifically, the post-label delay (PLD), i.e. the time between the end of the labeling period and the image acquisition, was varied either with or without additional application of crusher gradients to suppress intravascular signal contributions. The overall sensitivity change for varying the PLD between 1000 and 1700 ms was low. A tissue transit time from the neck to an axial supraventricular section through Broca's knee was obtained by fitting the PLD dependence to a two-compartment model. Averaging over subjects yielded 1930 +/- 110 ms for the tissue transit time, and 73 +/- 5 ml min(-1) 100 g(-1) for the cerebral blood flow. Small areas that exhibited a very high signal change upon labeling were indicative of regional variation in cerebral blood flow related to vascular anatomy.

Adult↗
PubMed1984

Distance measurements in spin-labeled lysozyme.

The single His-15 of hen egg lysozyme reacts with 2,2,6,6-tetramethyl-4-(bromoacetamido)piperidinyl-1-oxy or 2,2,5,5-tetramethyl-3-(bromoacetamido)pyrrolidinyl-1-oxy to give a spin-labeled enzyme [Wien, R. W., Morrisett, J. D., & McConnell, H. M. (1972) Biochemistry 11, 3707-3716]. High-field 1H NMR spectra (300 and 500 MHz) of these species in 2H2O contain protein peaks selectively broadened by dipolar coupling to the unpaired electron spin. While usually difficult to discern in the spectrum itself, broadened resonances are revealed in difference spectra obtained by subtracting the original spectrum from one taken after reduction of the nitroxide radical with ascorbate. The heights of difference spectra peaks are related in a simple way to r-6, where r is the label to proton distance. These distances were used to solve for the location of the electron spin by using algorithms from distance geometry. The spin was found to lie in a hydrophobic groove between Phe-3 and Asp-87. These results demonstrate the feasibility of spin-labeling for accurate distance measurements in proteins through the use of distance geometry.

Amino Acids↗
PubMed1997

Interactions of alpha-lactalbumin with fatty acids and spin label analogs.

Bovine alpha-lactalbumin (alpha-LA) has been shown by intrinsic protein fluorescence and electron spin resonance methods to interact with the spin-labeled fatty acid analog, 5-doxylstearic acid, as well as stearic acid. An intrinsic fluorescence titration of various alpha-LA forms with 5-doxylstearic acid causes first an increase and then a decrease in emission intensity with concomitant shifts in tryptophan emission wavelength. In some cases, up to three steps in the fluorescence titration curves were visible, which were fit to apparent binding steps from 10(-6) to 10(-4) M. The binding parameters of 5-doxylstearic acid for apo- and Ca2+-alpha-LA were an order of magnitude different from one another; the stronger one, apo-alpha-lactalbumin, exhibited a Kd of 35 microM. Electron spin resonance titrations of 5-doxylstearic acid-loaded apo-alpha-LA with stearate (micelles) seem to suggest separate binding loci if alpha-LA indeed binds stearate at these concentrations. The titration of alpha-LA by stearic acid results in a fluorescence emission red shift and an apparent stepped increase in fluorescence intensity. Lipid-protein association occurred at concentrations at which stearic acid micelles and aggregates begin to form in the absence of protein. Nonetheless, the relatively strong association between stearic acid and apo-alpha-LA was also confirmed by means of the fluorescent indicator acrylodated fatty acid binding protein, in which addition of alpha-LA to the stearate-loaded indicator protein reverses the decrease in fluorescence of the acrylodan chromophore conjugated to the protein.

Animals↗
PubMed1999

Linewidth analysis of spin labels in liquids. I. Theory and data analysis.

We present a method of simulating the EPR spectra of spin labels in liquids using direct convolution of hyperfine splitting with Lorentzian linewidths. The aim is to simulate the experimental lineshape by considering all spectrometer characteristics as well as inhomogeneous and homogeneous linewidth effects. A major advance in this method is the correction for the broadening produced by Zeeman modulation commonly used to obtain EPR signals; this allows experimenters much more freedom to optimize their experimental conditions for the best signal-to-noise ratio. Microwave power broadening (saturation) effects on the EPR lines are significant even at very low observer levels. Successful simulation requires that all contributions from unresolved hyperfine splittings be explicitly included. Inhomogeneous broadening is dealt with by including all spins that interact with the electron (as a set of superhyperfine interactions); there is no "effective Gaussian" to substitute for the correct superhyperfine interactions. The effects of spin exchange on the linewidth and lineshape can be observed and must be taken into account in order to extract the fundamental linewidths.

Computer Simulation↗
PubMed1993

The effect of annexin IV and VI on the fluidity of phosphatidylserine/phosphatidylcholine bilayers studied with the use of 5-deoxylstearate spin label.

An effect of annexin IV and VI on the fluidity of phosphatidylserine/phosphatidylcholine (PS/PC) membranes was studied by spin labeling technique with the use of 5-doxylstearic acid. It was found that calcium ions at micromolar concentrations induced a marked decrease in the order parameter of PS/PC membranes. This effect was completely abolished by both annexins. The influence of annexins on the mobility of fatty acid chains in the studied region in PE/PC membranes was insignificant.

Annexin A4↗
PubMed1973

Spin-labeling studies on the membrane of a facultative thermophilic bacillus.

Spin-labeling studies were conducted to elucidate the rigidity and viscosity of the membrane of a facultative thermophilic bacillus. By employing nitroxide stearate probes, it was observed that this fatty acid was incorporated into the membrane fraction. Electron spin resonance spectroscopy indicated that cells grown at 55 C contained a membrane which was more rigid and viscous than the membrane from cells grown at 37 C.

Bacillus↗
PubMed2006

An ESR spin-label study on molecular mobility in the interface between microphases of a diblock copolymer: effects of admixture of homopolymers that are miscible with one of the blocks.

Molecular mobility in the interfacial region of a microphase-separated structure was studied in binary mixtures of AB-type diblock copolymers and homopolymers (miscible with only A) by the spin-label technique. In this study, we prepared (a) binary blends of polystyrene-block-poly(methyl acrylate) (PS-block-PMA) and homopolymer poly(cyclohexyl acrylate)'s having the number-averaged molecular weight (Mn) of 1000 (PCHA-S) and (b) having the Mn of 17300 (PCHA-L), and (c) binary mixtures of the PS-block-PMA and homopolymer PS with the Mn of 900 (PS-1). Emphasis was placed on effects of the molecular weight and the miscibility of added homopolymers on the mobility in the interfacial region of the microphase separation. Selective incorporation of the added PCHA-S, PCHA-L, and PS-1 into the PS phase of the PS-block-PMA was confirmed by modulated-temperature differential scanning calorimetry (MDSC) measurement as a decrease in the glass transition temperature of the PS phase. Moreover, the MDSC and small-angle X-ray scattering (SAXS) measurements suggested that the spatial distributions of the PCHA-S and PS-1 in the PS phase were relatively uniform because of their small Mn. On the other hand, the distribution of the PCHA-L in the PS phase was somewhat heterogeneous because of the large Mn of the PCHA-L. The spin-label at the junction point of the PS-block-PMA allowed us to estimate the mobility in the interfacial region of the microphase separation. Influence of the PCHA-S and PCHA-L on the mobility in the interfacial region was negligible even though the relatively uniform distribution of the PCHA-S in the PS phase was suggested by the SAXS and MDSC. More uniform distribution of the PS-1 than that of the PCHA-S in the PS phase was suggested by the SAXS, and the mobility in the interfacial region was slightly enhanced by the addition of the PS-1. However, the mobility was almost constant against an increase in the PS-1. The PS-1 was considered to be penetrated into the interfacial region and activated the mobility, but the fraction of the PS-1 in the interfacial region was constant irrespective of the blended amount of the PS-1. These results suggest that effects of homopolymers on the mobility in the interface are significantly related to their spatial distribution in the host phase.

Journal Article↗
PubMedDate not supplied

[Segmental flexibility of Fc-region of spin labeled 2 subclasses of IgG molecule from cow blood and local conformational mobility of their carbohydrate components].

Spin-label was bound to carbohydrates of Fc-region of two subclasses of the IgG molecule from the blood serum of healthy and ill cows. By the value of rotational correlation time (10 nsec) internal flexibility of Fc-region of both IgG subclasses and by value of the order parameter (S = 0.9)--rigid attachment of oligosaccharide chains to protein parts of the molecules were found. At the same time the states of IgG1 an IgG2 molecules determined by dynamic steric characteristics for ill and healthy cows did not differ.

Animals↗
PubMed1972

Spin-label studies of dynamics of lipid alkyl chains in biological membranes: role of unsaturated sites.

Cultures of a yeast mutant, deficient in the synthesis of unsaturated fatty acids, were supplemented with either stearolic acid or with any one of three octadecanoic acids having a cis double bond 6, 9, or 11 carbons away from the acyl group. The resulting cells, with lipid alkyl chains well defined with respect to the position and nature of unsaturated sites, were then studied with spin-labeled stearic acids having a N-oxyloxazolidine ring located at 4, 6, 9, or 12 carbons away from the acyl group, and added in vitro to the cellular preparations. Differences in the molecular motion of each spin label were observed, as a function of the unsaturated site, in the intact yeast cells. Characteristic order to disorder phase transitions are inferred from data of temperature dependence. The results also indicate that triple bonds and cis double bonds inhibit a relatively ordered packing of lipid alkyl chains in the region between unsaturated sites and terminal methyl groups, leaving the hydrophobic region bounded by acyl groups and unsaturated sites unaffected.

Acylation↗
PubMed1995

The difference between ADP-beryllium fluoride and ADP-aluminium fluoride complexes of the spin-labeled myosin subfragment 1.

Electron paramagnetic resonance (EPR) spectroscopy was used for investigation of the structure of spin-labeled myosin subfragment 1 (S1) containing ADP and phosphate analogues, such as orthovanadate, aluminium fluoride (AlF4), and beryllium fluoride (BeFx). It has been shown that the local conformational changes in the region of Cys-707, induced by formation of the S1-ADP-BeFx complex, differ from those of S1 containing ADP-AlF4 or other phosphate analogues but are similar to the changes which occur in the presence of ADP or ATP gamma S. It is suggested that S1-ADP-AlF4 and S1-ADP-BeFx complexes represent structural analogues of different transition states of the ATPase cycle, namely the intermediate states S1**-ADP-P(i) and S1*-ATP, respectively.

Adenosine Diphosphate↗
PubMedDate not supplied

[Study of the flexibility of serum albumin molecules using the spin label method].

In is shown that the description of the motion character of N.- O-group of spin label conjugated with human serum albumin molecule on the basis of the jump--way isotropic diffusion model is correct. The structural flexibility of serum albumin molecule was revealed. It is the result of the ability of three domains that form the molecule for relative thermal reorientations. General tendency of elevation of protein correlation time from 20 to 45 ns with rising temperature from 5 to 44 degrees reflects the strengthening of hydrophobic interactions between domains. The presence in solution of 5 and 15% D2O essentially increases the amplitude of protein flexibility changes in the range of two thermoinduced transitions of serum albumin: 15-20 degrees and 32-35 degrees C. It reflects the important role of water in this process.

Chemical Phenomena↗
PubMed1978

Oxalate and spin-labeled oxalate as probes of the anion binding site of human transferrin. Metal to anion distance.

The spin-labeled anion N-[4-(2,2,6,6-tetramethylpiperidin-1-oxyl)] oxamate has been synthesized and characterized. In the presence of this compound, a specific iron-transferrin-anion complex is formed, as evidenced by the development of a characteristic red color. No EPR signal was observed for the nitroxyl radical in the protein complex, presumably due to broadening of the signal by the paramagnetic metal ion. Failure to observe a signal implies that the metal to nitroxyl distance is less than or equal to 6 A. This suggests that the anion is directly attached to the metal ion in the protein. The pH dependence of iron dissociation from iron-transferrin-oxalate is also reported. This complex is more stable at low pH than iron-transferrin-carbonate.

Binding Sites↗
PubMed1979

Spin-labelling of sialic acid in soluble and cell-surface glycoproteins.

A new, mild method is described for spin-labelling sialic acid residues in situ. The procedure involves the formation of C-1 sialamides and has been applied to a serum glycoprotein, a mucin, tissue sections from human colon, and erythrocyte membrane components. The selectivity of the method and its possible applicability to other types of labelling are discussed.

Colon↗
PubMed2005

Quantification of perfusion fMRI using a numerical model of arterial spin labeling that accounts for dynamic transit time effects.

A new approach to modeling the signal observed in arterial spin labeling (ASL) experiments during changing perfusion conditions is presented in this article. The new model uses numerical methods to extend first-order kinetic principles to include the changes in arrival time of the arterial tag that occur during neuronal activation. Estimation of the perfusion function from the ASL signal using this model is also demonstrated. The estimation algorithm uses a roughness penalty as well as prior information. The approach is demonstrated in numerical simulations and human experiments. The approach presented here is particularly suitable for fast ASL acquisition schemes, such as turbo continuous ASL (Turbo-CASL), which allows subtraction pairs to be acquired in less than 3 s but is sensitive to arrival time changes. This modeling approach can also be extended to other acquisition schemes.

Algorithms↗
PubMed1998

Partitioning and localization of spin-labeled amantadine in lipid bilayers: an EPR study.

EPR was used to study the distribution of the spin-labeled amantadine (AA-SL) between the bulk hydrophobic-hydrocarbon solvent, light paraffin oil, and water and between hydrophobic-hydrocarbon chain region of lipid membranes and water. The AA-SL molecules were soluble in both hydrophobic and polar regions of investigated systems. It was shown that the partition coefficient of AA-SL between the hydrocarbon region of the L-alpha-dimyristoylphosphatidylcholine fluid-phase membrane and water is much higher than between bulk hydrocarbon solvent and water. Furthermore, the partitioning of AA-SL into membranes of multilamellar liposomes made of L-alpha-dimyristoylphosphatidylcholine, L-alpha-dipalmitoylphosphatidylcholine, and L-alpha-distearoylphosphatidylcholine was studied as a function of temperature, indicating no abrupt change at the main phase transition of these membranes. It is also clear from our data that AA-SL can penetrate into the gel-phase membrane practically with the same partitioning as into the fluid-phase membrane. Furthermore, it was shown that at least part of the AA-SL molecule is deeply buried in the hydrocarbon chain region of the membrane.

Amantadine↗
PubMed1986

Glutaryl phosphatidylcholine effects on pH and composition dependent behavior of liposomes studied by spin-labeling method.

The influence of glutaryl phosphatidylcholine on the molecular organization of phosphatidylcholine liposomes was studied by spin-labeling technique. The ESR signals given by the 5-nitroxide stearic acid label showed that the presence of glutaryl lecithin (i) significantly increased the negative charge density of the polar liposome surface with increasing proton concentration depending on the bulk solution pH, and (ii) apparently decreased the packing (order) of the hydrophobic region close to the surface, essentially in the presence of saturated phospholipids. The spectral information--S (order parameter) and alpha N (isotropic nitrogen coupling constant)--resulted in the location of the probe near or in the polar zone of the membrane or in the hydrophobic region, depending on the protonation/deprotonation of the fatty acid carboxyl group of the probe. The microviscosity of the inner region of the membrane monitored by the 12- and 16-probes was not significantly altered by glutaryl lecithin. On the other hand, glutaryl lecithin has a lesser effect on liposomes containing anionic polar head groups, such as dipalmitoyl phosphatidylglycerol or phosphatidylinositol, the anionic charge of which already had the same effect on protonation of the polar surface. The temperature dependence of dipalmitoyl phosphatidylcholine liposome dynamic behavior indicates that the glutaryl lecithin effect is completely different above and below the gel-to-liquid crystalline phase transition point.

Adenosine↗
PubMed1983

Lower levels of erythrocyte membrane fluidity in diabetic patients. A spin label study.

The dynamic properties of intact erythrocyte membrane in diabetic patients were investigated by means of electron spin resonance using three stearic acid spin labels (SAL): 5-, 12-, and 16-SAL. Significantly lower levels of erythrocyte membrane fluidity were revealed with 16-SAL as a probe in diabetic patients when compared with normal controls. However, there were no significant differences in fluidity values using 5- or 12-SAL between the two groups. Therefore, it became obvious that the decrease in fluidity was located in deeper sites (hydrophobic region) of the erythrocyte double membrane in diabetic patients. It was strongly suggested that changes in the membrane cholesterol to phospholipid molar ratios are not a principal factor contributing to the fluidity change. A significant increase of sphingomyelin and decrease of phosphatidylethanolamine were found in the erythrocyte membrane of diabetic patients and an alteration in membrane phospholipid classes and their acyl-chains could conceivably be related to the fluidity change. There were no significant correlations between change in membrane fluidity and most plasma lipids, plasma lecithin-cholesterol acyl-transferase activities, erythrocyte glycosylated hemoglobin, erythrocyte adenosine triphosphate, fasting blood glucose or duration of the disease. Plasma cholesterol of high-density lipoprotein showed a significant negative correlation with the membrane fluidity values. Some of the possible factors contributing to and the significance of the lower levels of erythrocyte membrane fluidity were discussed in conjunction with both metabolic and clinical aspects in diabetic patients.

Adenosine Triphosphate↗