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PubMed2006

Synthesis and structure of a nucleoside with pi-conjugated nitroxide spin label forming a one-dimensional ferromagnetic chain.

Spin labeled 2'-deoxyuridine, in which a significant fraction of the spin density is delocalized from a nitroxide radical to the DNA base residue, was prepared as a crystalline solid, stable at ambient conditions. The crystal packing, which includes multiple hydrogen bonds, leads to one-dimensional chains of molecules with predominant intrachain ferromagnetic coupling and weaker interchain antiferromagnetic coupling.

Magnetics↗
PubMed1978

The lipid-protein interaction in the membrane-bound Na+, K+-ATPase: a spin label study.

The interrelated temperature induced structural changes in the protein and lipid fractions of the Na+, K+-ATPase preparations were studied. A spin-labelled analog of ATP (ATP) was used, where the paramagnetic fragment was attached to the 2' (3')-OH ribose group. It is shown that the rotational mobility of ATP changes with the temperature in a discontinuous way. This correlates with the behaviour of the enzymatic activity of Na+, K+-ATPase and with the state of lipids in the enzyme preparations, both being characterized by a break in the 20-23 degrees C temperature region. When the Mn2+ ions were substituted by Mn2+ a strong magnetic dipolar interaction between the spin label in ATP and the Mn2+ ion was observed, which proves that the complex E-ATP--Mn2+ is formed before the hydrolysis of ATP. The structural changes which occur near 20 degrees C were also observed in the neighbourhood of the SH-groups modified by spin label X, an analog of maleimide. The structural changes observed support the idea that the protein-lipid interactions in the Na+, K+-ATPase provide the relaxation of the system from the unstable state during hydrolysis of ATP and cation transport.

Adenosine Triphosphatases↗
PubMed1988

Interdigitated lipid bilayers of long acyl chain species of cerebroside sulfate. A fatty acid spin label study.

The metastable phase behavior of semi-synthetic species of cerebroside sulfate (CBS), with hydroxy and non-hydroxy fatty acids from 16 to 26 carbons in length, was compared in Li+ and K+ using differential scanning calorimetry. The structure of the metastable and various stable phases formed in the presence of these two cations was investigated using a fatty acid spin label, 16-doxylstearate. A number of stable phases with successively higher phase transition temperatures and enthalpies occur in the presence of K+ (see the preceding paper). Li+ prevents formation of the most stable phases with the highest transition temperatures and enthalpies for all species of CBS. However, it does not prevent a transition from the metastable phase to the first stable phase of the longer chain C24 and C26 species. Furthermore, it allows C24:0h-CBS to undergo a similar transition, in contrast to a high K+ concentration, which prevents it. The spin label has anisotropic motion in the metastable gel phase formed by all species of CBS on cooling from the liquid crystalline phase. The spectra resemble those in gel phase phospholipids. The spin label is partially insoluble in the most stable phases formed by all the lipids, including the unsaturated C24:1 species, preventing further elucidation of their structure using this technique. However, the spin label is soluble in the first stable phase formed on cooling by the longer chain C24:0 and C26:0-CBS in Li+ and K+ and by C24:0h-CBS in Li+, and is motionally restricted in this phase. The motional restriction is similar to that observed in the mixed interdigitated bilayers of asymmetric species of phosphatidylcholine and fully interdigitated bilayers formed by symmetric phospholipids. It strongly suggests that the highly asymmetric long chain species of CBS form a mixed interdigitated bilayer in their first stable gel phases while the metastable phase of these and the shorter chain lipids may be partially interdigitated. The metastable phase of C24:1-CBS is more disordered suggesting that it may not be interdigitated at all. Thus the results suggest that (i) the hydroxy fatty acid inhibits but does not prevent formation of a mixed interdigitated bilayer by long chain species of CBS, (ii) an increase in non-hydroxy fatty acid chain length from 24 to 26 carbons promotes it, and (iii) a cis double bond probably prevents any form of interdigitation. These results may be relevant to the physiological and pathological roles of these structural modifications of CBS.

Animals↗
PubMed1990

Lipid-protein interactions in stacked and destacked thylakoid membranes and the influence of phosphorylation and illumination. Spin label ESR studies.

The effects of membrane destacking, protein phosphorylation, and continuous illumination have been studied in pea thylakoid membranes using ESR spectroscopy of an incorporated spin-labelled phosphatidylglycerol. This spin-labelled analogue of an endogenous thylakoid lipid has previously been shown to exhibit a selectivity of interaction with thylakoid proteins. Neither destacking, phosphorylation nor illumination was found to change the ESR spectra appreciably, suggesting that for phosphatidylglycerol at least, neither the number of protein-associated membrane lipids nor their pattern of selectivity was altered. The redistribution of the thylakoid protein complexes in the membrane, under these various conditions, therefore takes place with conservation of the properties of the lipid/protein interface.

Cell Membrane↗
PubMed1984

Spin-label studies of the oligomeric structure of band 3 protein in erythrocyte membranes and in reconstituted systems.

A spin-labeled fatty acid (16-doxylstearic acid), linked by an ester bond to a maleimide or a nitrene residue, was covalently attached to band 3 of erythrocyte membranes. The electron spin resonance spectrum of the spin-labeled protein was examined at different temperatures in: (a) whole erythrocyte ghosts; (b) ghosts depleted of spectrin and actin; (c) alkaline-treated ghosts; (d) vesicles made with purified band 3 reassociated with dimyristoylphosphatidylcholine. Most spectra are composite with a major component corresponding to a large overall splitting. The determination of the percentage of the immobilized component was carried out by pairwise subtraction. At low temperatures (1-7 degrees C), the highest fraction of immobilized component was found in dimyristoylphosphatidylcholine vesicles (approx. 100%); alkaline-treated membranes had approx. 75% of the immobilized component at the same temperature; whole erythrocyte, spectrin/actin-depleted and spectrin/actin/ankyrin-depleted ghosts gave identical results (approx. 60% of immobilized component). The immobilized fraction decreased in all samples with increasing temperature or addition of a nonsolubilizing concentration of dodecyl octaethylene glycol monoether. In dimyristoylphosphatidylcholine vesicles, however, the modification in the ration of the two components was obtained only above the lipid transition temperature (23 degrees C). The strong immobilization of the spin-labeled lipid chain at all temperatures suggested trapping of the lipid chain between proteins. At low temperature, in dimyristoylphosphatidylcholine vesicles or in alkaline-treated ghosts, lipid-protein segregation is likely to take place. In whole erythrocyte ghosts, on the other hand, the large contribution of the motionally restricted component at physiological temperature indicates the oligomeric nature of band 3. Partial dissociation of the oligomers occurs as the temperature is increased, but the presence or absence of cytoskeletal proteins has no influence on the state of oligomerization of band 3.

Actins↗
PubMed1975

Orientation dependence in the Epr spectra of spin labels in glycerinated muscle fibres.

Glycerinated muscle fibres labelled with a set of five-membered maleimide spin labels revealed a complex type epr spectra, which showed a reduced rate of anisotropic motion. The spectra can be interpreted in terms of the ratio of the two down-field peaks and of the hyperfine coupling constant. The spectra clearly indicated that the preferred orientation of the 2peta molecular orbital of the odd electron is perpendicular rather than parallel to the long axis of the muscle fibres. Increasing chain length between the meleimide ring and pyrrolidine nitroxide ring reduces the orientational anisotropy. Thermal denaturation destroys the orientation dependence of the epr spectra of spin labels. The Mg-ATP induced shortening of the fibres influences the spectral parameters. The fibers which had been contracted showed a modified orientation dependence of epr spectra.

Animals↗
PubMed1986

Conformational alterations within the glycocalyx of erythrocyte membranes studied by spin labelling.

The structure of the glycocalyx of the membrane of human erythrocytes and spectrin-depleted vesicles was studied under various conditions by two spin-labelling approaches: covalently labelling sialic acid residues of the glycocalyx and incorporation of a charged hydrophobic spin probe, CAT 16, being sensitive to alterations on the membrane surface into the lipid phase. Although cell electrophoretic measurements which were performed, additionally, indicated an erection of the glycocalyx upon decreasing the ionic strength of the suspension medium a more restricted mobility of spin-labelled sialic acid residues was found, in this case probably due to electrostatic interactions. The enhanced mobility of the spin probe CAT 16 at low ionic strength as well as in the case of neuraminidase-treated cells could be caused by reduced steric and electrostatic interaction with glycoproteins and glycolipids. La3+ adsorption and virus attachment on the human erythrocyte membrane were accompanied with a reduced mobility of sugar headgroups of the surface coat. No indication of cluster formation or lateral segregation of glycophorin molecules was found upon virus binding. After denaturation of the spectrin cytoskeleton of intact erythrocytes, increased mobility of spin-labelled sialic acid residues was observed.

Electron Spin Resonance Spectroscopy↗
PubMed1982

Preparation of spin-labeled poly(U) and its activity in assays with eukaryotic ribosomes.

ESR studies on the interaction of spin-labeled polynucleotides with ribosomes require a sufficient label-to-nucleotide ratio. Using three different spin labels (SL) we have elaborated a technique to label poly(U) up to a ratio of 1 SL per 30 uridine residues. This ratio is much higher than maximal values obtained by other authors. The SL-poly(U) was shown to have the same activity as unlabeled poly(U) to direct synthesis of poly(Phe). SL-poly(U) binds to rat liver ribosomes in the presence of Mg2+ as shown by ESR. Titration with EDTA leads to a release of SL-poly(U) from ribosomes.

Animals↗
PubMed1999

Bioreduction of Tempone and spin-labeled gentamicin by gram-negative bacteria: kinetics and effect of ultrasound.

The primary objective of this study is the investigation of bioreduction kinetics of hydrophilic spin probes, 2,2,6,6, -tetramethyl-4-oxo-piperidinyl-1-oxyl (Tempone), and spin-labeled antibiotic gentamicin by gram-negative bacteria maintained at various oxygen tensions, with emphasis on the effect of probe penetration rate. This information was used to evaluate the effect of ultrasound on the penetration of hydrophilic compounds, including antibiotics, into Pseudomonas aeruginosa and Escherichia coli cells. Penetration of spin-labeled compounds into the cells was assessed by the reduction rate of the nitroxyl moiety measured by EPR. In cell suspensions, both Tempone and spin-labeled gentamicin were localized predominantly in the aqueous phase surrounding the cells. However, a gradual reduction of the probes in contact with the cells indicated that the probes penetrated through the outer membrane and periplasmic space into the cytoplasmic membrane, where the electron transport chains and other metabolic activities of gram-negative bacteria are localized. The kinetics of probe reduction depended on oxygen tension and presence of electron transport chain blockers. It was found that probe penetration rate through the outer cell membrane affected the rate of probe reduction; damaging the permeability barrier by cell incubation with EDTA or by powerful insonation above the cavitation threshold increased the rate of probe reduction. In contrast, insonation below the cavitation threshold did not affect the rate of probe reduction. These findings imply that the recently observed synergistic effect between hydrophilic antibiotics and low frequency ultrasound in killing gram-negative bacteria did not result from the enhanced antibiotic penetration through bacterial cell walls.

Cell Membrane↗
PubMed1990

NMR, calorimetric, spin-label, and optical studies on a trifluoromethyl-substituted styryl molecular probe in dimyristoylphosphatidylcholine vesicles and multilamellar suspensions: a model for location of optical probes.

NMR, calorimetric, and optical spectroscopic studies have been performed on a trifluoromethyl-substituted styryl molecular probe bound to vesicles and multilamellar suspensions formed from dimyristoylphosphatidylcholine (DMPC). In the fluorine NMR spectrum at 35 degrees C there are two partially resolved resonances, but these collapse to an apparently single resonance at temperatures above 60 degrees C. However, a line-shape analysis is not consistent with exchange between two sites on an NMR time scale, and the two resonances are assumed to be due to probe sites in the inner and outer leaflets of the vesicles. Two fluorescence lifetimes, each associated with one of these sites, characterize the decay curves for the molecular probe bound to DMPC vesicles. The shift reagent Eu(FOD)3 and several nitroxide spin labels covalently bound to lipophilic structures strongly attenuate the lower frequency component of the fluorine NMR spectrum and also shift the other resonance to higher frequencies. The effect of two spin labels on the probe fluorine T2 relaxation time has been used to estimate the distance between the spin label unpaired electron and the trifluoromethyl group. The location of the spin label site in the membrane was determined from the effect of the unpaired electron on the lipid 13C linewidths. A model for the location of the probe in the bilayer was developed from the above information and refined using molecular mechanics calculations on a probe-DMPC lipid complex. The long axis of the probe parallels the bilayer normal; the styryl-group portion of the optical chromophore is located slightly below the glycerol backbone, and the remainder of the chromophore extends well into the hydrophobic region of the bilayer. Therefore, the optical properties of the probe should not be significantly influenced by alterations of the membrane surface charge density. Parameters derived from DSC studies in the gel-to-lipid crystal phase transition of DMPC are extremely sensitive to the probe. Even at 0.0001 mol fraction of probe, the transition is substantially broadened, and the delta H for the transition has increased, just as one predicts for the formation of a tight complex described above.

Calorimetry↗
PubMed1980

A spin-label study of the effects of drugs on calcium release from isolated sarcoplasmic reticulum vesicles.

The effects of caffeine, thymol, and procaine on calcium release from fragmented sarcoplasmic reticulum (FSR) from rabbit skeletal white muscle were investigated by the spin label method at the organellar level. Two thiol-directed spin labels, 4-maleimide-2,2,6,6-tetramethylpiperidinooxyl and 4-(2-iodoacetamide)-2,2,6,6-tetramethylpiperidinooxyl, were used for the labeling of SR proteins. The ratio (W/S) of the weakly (W) and strongly (S) immobilized ESR signals was measured for the maleimide and iodoacetamide labeled FSR. The two labels gave different W/S values, which means that the two labels report conformational changes at different loci of SR proteins. The dependences of the W/S ratios on the concentration of the drugs showed that conformational changes of SR proteins induced by these drugs are not the same. From measurements of the distribution of 5-doxyldecanoic acid methylester between the lipid and water phases, it was found that the conformational changes of the SR proteins caused by thymol or procaine induced a disorder in local regions of the phospholipid bilayers of FSR, while such disordering was not induced by caffeine. On the other hand, caffeine and thymol showed definite effects on calcium release from FSR, while procaine did not. These results indicate that the effects of the drugs on the protein conformations can be well characterized at the organellar level by means of the spin label technique and that some specific changes in the conformations of SR proteins are necessary for calcium release from FSR.

Animals↗
PubMed1997

The interaction of lower alcohols with apoB in spin labeled human plasma low density lipoproteins (LDL).

In this study the interaction of alcohol with the macromolecular lipid-protein assembly represented by human plasma low density lipoproteins (LDL) was investigated. The spin label which covalently binds to the side chain amino group of lysines as well as terminal amino groups was attached to the spin labeled apoprotein (apoB) of native LDL in order to observe the protein component in the electron spin resonance (ESR) spectrum. The interaction of different lower alcohols (methanol, ethanol, propanol and butanol) with the spin labeled LDL was studied for two alcohol concentrations (0.3 and 3.0 M). The ESR spectra indicate a decrease of the hyperfine splitting and narrowing of the linewidth upon the action of alcohol that leads to the conclusion that alcohol provokes a change in the apoB conformation. These findings are explained by following the arguments of the phospholipid mediated mechanism of alcohol action, through the modulation of the lipid packing free volume which results in the protein conformational change.

Alcohols↗
PubMed1979

Lipid-protein interactions in membranes: effect of lipid composition on mobility of spin-labeled cysteine residues in yeast plasma membrane.

In order to gain direct evidence for lipid-dependent protein conformation in membrane, effects of modification of lipid composition on mobility of spin-labeled cysteine residues were investigated in the plasma membrane of the yeast Saccharomyces cerevisiae. Conversion of the bulk of phospholipids to diglycerides by treatment of the membrane with phospholipase C substantially enhanced spectral anisotropy. However, alterations of the viscosity of the lipid-bilayer by enriching the membrane with palmitelaidic or oleic acid had no effect on mobility of spin-labeled cysteine residues. These observations indicate that while the spin-labeled residues are not in direct contact with the lipid core of the membrane, there are lipid-protein interactions to the extent that removal of the polar portion of the bulk of phospholipids induces conformational changes in proteins, which in turn restrict mobility of these residues. It is concluded that conformation of membrane proteins on lipid structure and that phospholipids have a role in preserving the native conformation of proteins.

Adenosine Triphosphatases↗
PubMed1992

Oxygen diffusion-concentration product in rhodopsin as observed by a pulse ESR spin labeling method.

Permeation of molecular oxygen in rhodopsin, an integral membrane protein, has been investigated by monitoring the bimolecular collision rate between molecular oxygen and the nitroxide spin label using a pulse electron spin resonance (ESR) T1 method. Rhodopsin was labeled by regeneration with the spin-labeled 9-cis retinal analogue in which the beta-ionone ring of retinal is replaced by the nitroxide tetramethyl-oxypyrrolidine ring. The bimolecular collision rate was evaluated in terms of an experimental parameter W(x), defined as T1(-1)(air,x)--T1(-1)(N2,x) where T1's are the spin-lattice relaxation times of the nitroxide in samples equilibrated with atmospheric air and nitrogen respectively, which is proportional to the product of local oxygen concentration and local diffusion coefficient (transport). W-values at the beta-ionone binding site in spin-labeled rhodopsin are in the range of 0.02-0.13 microseconds-1, which are 10-60 times smaller than W's in water and 1.1-20 times smaller than in model membranes in the gel phase, indicating that membrane proteins create significant permeation resistance to transport of molecular oxygen inside and across the membrane. W(thereby the oxygen diffusion-concentration product) is larger in the meta II-enriched sample than in rhodopsin, indicating light-induced conformational changes of opsin around the beta-ionone binding site. W decreases with increase of temperature for both rhodopsin and meta II-enriched samples, suggesting that temperature-induced conformational changes take place in both samples. These changes were not observable using conventional ESR spectroscopy. It is concluded that W is a sensitive monitor of conformational changes of proteins.

Animals↗
PubMed1981

An in vitro ESR study of uncatalyzed rat liver protein-catalyzed spin-labeled phosphatidylcholine exchange.

ESR spectrometry has been used to study fatty acid spin-labeled phosphatidylcholine exchange from single bilayer donor vesicles to various acceptor systems, such as intact or differently treated mitochondria, phospholipid multilamellar vesicles or single bilayer vesicles. This exchange is catalyzed by soluble non-specific rat liver protein, first investigated by Bloj and Zilversmit in 1977 (J. Biol. Chem. 252, 1613--1619). Non-catalyzed phosphatidylcholine exchange has also been studied. Full inhibition of both mechanisms occurs with lipid-depleted acceptor mitochondria, while N-ethylmaleimide-treated mitochondria behave as good acceptors during catalyzed exchange but are in no way effective during spontaneous exchange. Non-catalyzed exchange does not take place with phospholipase D-treated mitochondria as acceptors, while the pure catalyzed mechanism is inhibited by 28%. Neither multilamellar nor single bilayer phospholipid vesicles exchange spin-labeled phosphatidylcholine in the absence of protein, the former being a poorer acceptor system than the latter during catalyzed exchange, when this activity is 31 and 80%, respectively, of that of intact mitochondria. The hypothesis is made that the spontaneous mechanism is active among intact natural membranes and could be of some importance in vivo. Furthermore, the biomembrane protein moiety is assumed to be involved in the catalyzed exchange more as a phospholipid spacer than as a binder between the exchange protein and the membrane involved. Phospholipids, on the contrary, appear to be important for both functions.

Animals↗
PubMed1979

The nature of the substrate inhibition in lactate dehydrogenases as studied by a spin-labeled derivative of NAD.

The formation of the ternary complex of lactate dehydrogenase (L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) from pig heart and skeletal muscle with the adduct of pyruvate to NAD", spin-labeled at N6 was studied by ultraviolet spectroscopy and ESR techniques. According to ultraviolet measurements we found identical binding characteristics for the natural coenzyme and its spin-labeled analog. The rate by which the ESR signal of free spin-labeled NAD+ decreased upon addition of pyruvate to the binary complexes was substantially different in the two isozymes. With the heart type an initial drop followed by a further linear decrease, zero order in the enzyme and coenzyme concentration was observed. In case of the skeletal muscle isozyme no immediate reaction and a first order process occurred. The initial reaction can be attributed to a non-covalent enzyme/spin-labeled NAD+/pyruvate complex with a dissociation constant for pyruvate of 11 +/- 1 mM, thus explaining the well-known substrate inhibition in the heart isozyme above 2 mM pyruvate. The further reaction is then determined by the buffer dependent enolization of pyruvate. In the muscle isozyme formation of the covalent adduct is not assisted by prior binding of pyruvate in a non-covalent ternary complex and therefore the rate depends on the binary complex concentration.

Animals↗
PubMed2006

Identification of pH-sensitive regions in the mouse prion by the cysteine-scanning spin-labeling ESR technique.

We analyzed the pH-induced mobility changes in moPrP(C) alpha-helix and beta-sheets by cysteine-scanning site-directed spin labeling (SDSL) with ESR. Nine amino acid residues of alpha-helix1 (H1, codon 143-151), four amino acid residues of beta-sheet1 (S1, codon 127-130), and four amino acid residues of beta-sheet2 (S2, codon 160-163) were substituted for by cysteine residues. These recombinant mouse PrP(C) (moPrP(C)) mutants were reacted with a methane thiosulfonate sulfhydryl-specific spin labeling reagent (MTSSL). The 1/deltaH of the central (14N hyperfine) component (M(I) = 0) in the ESR spectrum of spin-labeled moPrP(C) was measured as a mobility parameter of nitroxide residues (R1). The mobilities of E145R1 and Y149R1 at pH 7.4, which was identified as a tertiary contact site by a previous NMR study of moPrP, were lower than those of D143R1, R147R1, and R150R1 reported on the helix surface. Thus, the mobility in the H1 region in the neutral solution was observed with the periodicity associated with a helical structure. On the other hand, the values in the S2 region, known to be located in the buried side, were lower than those in the S1 region located in the surface side. These results indicated that the mobility parameter of the nitroxide label was well correlated with the 3D structure of moPrP. Furthermore, the present study clearly demonstrated three pH-sensitive sites in moPrP, i.e., (1) the N-terminal tertiary contact site of H1, (2) the C-terminal end of H1, and (3) the S2 region. In particular, among these pH-sensitive sites, the N-terminal tertiary contact region of H1 was found to be the most pH-sensitive one and was easily converted to a flexible structure by a slight decrease of pH in the solution. These data provided molecular evidence to explain the cellular mechanism for conversion from PrP(C) to PrP(Sc) in acidic organelles such as the endosome.

Animals↗
PubMed1986

Probing of mRNA binding sites involved in interactions with rat liver ribosomes using poly(U) spin labeled at the ribose moiety.

The interaction of rat liver ribosomes with poly(U), spin labeled (SL) at the 2'OH groups of ribose residues by N-(2,2,5,5-tetramethyl-3-carbonylpyrroline-1-oxyl)-imidazole, has been studied by electron spin resonance (ESR) spectroscopy. The ESR spectra demonstrate that SL-poly(U) with a modification of 1 spin label per 20 ribose residues binds to 80S ribosomes as well as to 40S subunits in a 1:1 stoichiometry at 12 mM MgCl2. The same result is found with highly modified poly(U) bearing 1 SL per 4 ribose residues. Addition of excessive amounts of unmodified poly(U) displaces bound SL-poly(U) from the ribosome which points to a competition for the same binding site at the ribosome. The biological activity of SL-poly(U) was tested with regard to trigger 80S ribosomes for binding of Phe-tRNAPhe and for poly(Phe) synthesis. SL-poly(U) bearing 1 SL group per 20 ribose residues directs the binding of only 50% of the amount of Phe-tRNAPhe bound to ribosomes in the presence of unmodified poly(U). When SL-poly(U) bearing 1 SL group per 4 ribose residues is used, this value drops to 25%. Poly(Phe) synthesis is even more impaired: In the presence of poly(U) bearing 1 SL-group per 20 ribose residues only about 30% of the amount of poly(Phe) coded by unmodified poly(U) are synthesized and in the presence of SL-poly(U) bearing 1 SL group per 4 ribose residues poly(Phe) synthesis is completely abolished. The results suggest that modification of the ribose moiety has only a relatively small influence on the binding of mRNA to ribosomes but causes substantial impairment of the mRNA function, whereas, as shown earlier (Ebert et al., Acta Biol. Med. Germ. 41, 431, 1982), modification of the base moiety of poly(U) (in a proportion of 1 SL per 30 bases) does not influence coding efficiency for poly(Phe) synthesis.

Animals↗