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881.
Red blood cells from mice infected with Plasmodium berghei and from uninfected mice were labeled with stable, free radical derivatives of stearic acid. Electron spin resonance spectra of these samples showed that the degree of molecular order in these membranes decreased, and the rate of motion of the probe increased, with increasing levels of parasitemia. Parasitemia increased the ratio of unsaturated to saturated 18-carbon fatty acids, and decreased the percentage of arachidonic acid and of cholesterol. The effects of parasitemia on the membrane properties correlated with decreases in cholesterol/fatty acid ratios. 相似文献
882.
C.R. Toppin I.E. Thomas E.V. Bobst A.M. Bobst 《International journal of biological macromolecules》1983,5(1):33-36
The synthesis of novel spin labelled deoxynucleoside-5′-triphosphates and their enzymatic incorporation with terminal deoxynucleotidyl transferase into DNA are described. 相似文献
883.
Shoji Takigami Machiko Shimada
Peter A. Williams
Glyn O. Phillips 《International journal of biological macromolecules》1993,15(6):367-371The order to disorder transition of xanthan molecules in aqueous solutions has been studied using e.s.r. spectroscopy. Nitroxide spin-label was covalently attached to carboxyl groups on the xanthan side chains. The e.s.r. spectra obtained for aqueous spin-labelled xanthan solutions at varying ionic strengths contained both isotropic and anisotropic components at room temperature. The anisotropic component was attributed to the association of the side chains with the xanthan cellulosic backbone and was found to be present in greater proportions at increasing ionic strength. The spectra gradually changed with rising temperature and the proportion of anisotropic component decreased. This spectral change reflected the disruption of the side chain association with the backbone during the conformational change. Hysteresis effects were observed following sequential heating and cooling cycles suggesting that chain aggregation occurred. 相似文献
884.
885.
《Journal of liposome research》2013,23(3):194-202
The effects of tricylic antidepressant clomipramine (CLO) on the membrane properties of saturated dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine as well as on unsaturated egg yolk phosphatidylcholine liposomes were investigated by the electron paramagnetic resonance spin-labeling technique, in combination with the simulation of the spectra, taking into account that the membrane is heterogeneous and composed of the regions with different fluidity characteristics. Different spin labels, monitoring membrane properties in the upper and inner parts of the membrane, were used. In general, two spectral components, having different motional characteristics, were detected in all liposomes investigated. In liposomes with saturated chains, CLO decreased the phase-transition temperature, disordered the membrane, and increased polarity in the upper part of the membrane. However, less impact was observed in liposomes with unsaturated chains. In dipalmitoyl phosphatidylcholine liposomes, it also induced molecular rearrangements near the pretransition temperature. The presence of 30 mol% cholesterol increased the fluidizing effect of CLO and modified the lateral diffusion of nitroxide in the inner part of the membrane. A unique anomalous increase in diffusion of nitroxide, dependent on CLO concentration, was detected in the temperature region where the phosphatidylcholine membrane without cholesterol experiences the phase transitions. Since the changes in the central part of the membrane were even more pronounced than in the upper part of the membrane, it could be concluded that CLO incorporates into the membrane with its hydrophobic ring parallel to the phospholipid chains. 相似文献
886.
S.E. Gasanov M.A. Alsarraj N.E. Gasanov E.D. Rael 《The Journal of membrane biology》1997,155(2):133-142
Membrane-active toxins from snake venom have been used previously to study protein-lipid interactions and to probe the physical
and biochemical states of biomembranes. To extend these studies, we have isolated from Naja naja kaowthia (cobra) venom a cytotoxin free of detectable phospholipase A2 (PLA2). The amino acid composition, pI (10.2), and net charge of the cytotoxin compares well with membrane-active toxins isolated
from venoms of other cobras. The cytotoxin, shown by a spin label method, associates with PLA2 in buffers at pH values between 7.0 and 5.0, but not at pH 4.0. It is suggested that cytotoxin and PLA2 (pI close to 4.8) associate electrostatically in the native venom. The effect of the cytotoxin on model phospholipid membranes
was studied by EPR of spin probes in oriented lipid multilayers and 1H-NMR of sonicated liposomes. The cytotoxin did not significantly affect the packing of lipids in pure phosphatidylcholine
(PC) membranes and in PC membranes containing 10 mol% phosphatidic acid (PA) or cardiolipin (CL). However, the cytotoxin induced
an increase in membrane permeability and formation of nonbilayer structures in PC membranes containing 40 mol% of PA or CL.
The purified cytotoxin was cytocidal to Jurkat cells, but had little effect on normal human lymphocytes. However, both Jurkat
cells and normal lymphocytes were killed equivalently when treated with 10−9
m PLA2 and 10−5
m cytotoxin in combination. From its effect on model membranes and Jurkat cells, it is suggested that purified cytotoxin preferentially
targets and disrupts membranes that are rich in acidic phospholipids on the extracellular side of the plasma membrane.
Received: 20 March 1996/Revised: 25 September 1996 相似文献
887.
Free Radicals in Rabbit Spinal Cord Ischemia: Electron Spin Resonance Spectroscopy and Correlation with SOD Activity 总被引:2,自引:0,他引:2
Vincenzo Lombardi Ladislav Valko Svorad Štolc Marián Valko Ol'ga Ondrejičková L'ubica Horáková Jan Plaček Antonio Troncone 《Cellular and molecular neurobiology》1998,18(4):399-412
1. In nonanesthetized rabbits temporal occlusion of the abdominal aorta was used to induce oxidative stress in the lower part of the body including distal segments of the spinal cord.2. Spinal cord samples were taken from the animals exposed to 25-min aortic occlusion (AO ) or to occlusion followed by 1- or 2-hr reperfusion (AO/R1 or AO/R2, respectively) or from sham-operated animals (C). The presence of free radicals (FR) in the spinal cord samples frozen in liquid N2 was assessed by ESR spectroscopy without spin trapping. Moreover, superoxide dismutase (SOD) activity and conjugated diene (CD) levels were measured in the samples.3. In the AO group FR were detected in the spinal cord regions close to the occlusion (lower thoracic and distal segments) along with a decrease in SOD activity. The calculated g value (g = 2.0291) indicated that the paramagnetic signal recorded might be attributed to superoxide radicals. FR were absent in the AO/R1 group. Concurrently, the SOD activity revealed a significant tendency to return to the control level. FR appeared again in the AO/R2 group, mostly in the upper and middle lumbar regions, along with a decrease in SOD activity. No sample from the C group revealed FR. A significant increase in CD levels was observed in the thoracolumbar region only in the AO/R2 group. The temporary absence of FR in the AO/R1 group suggests activation of defense antioxidant mechanisms (e.g., specific enzymatic systems such as SOD), which might have been exhausted later.4. Changes in SOD activity similar to those observed in the thoracolumbar region, though less noticeable, occurred in the obviously noncompromised tissue (upper cervical region). This points to a kind of generalized reponse of the animal to aortic occlusion.5. Direct ESR spectroscopy revealed the presence of FR as well as their time course in the spinal cord during the early phase of ischemia/reperfusion injury and the inverse relationship between FR and SOD activity. 相似文献
888.
P F Coleman 《Biochemical and biophysical research communications》1977,74(4):1544-1551
At pH 6.5 in a 0.05 bis-Tris-0.1 Cl? buffer, tetra aquo ferrihemoglobin A (HbA+) binds CN? with a Hill coefficient of n = 1.4. The Hill coefficient increases slightly and the average CN? affinity decreases in the presence of excess spin labeled triphosphate (SLTP). This is probably the result of the finding that the SLTP exhibits a twofold higher affinity for HbA+ than for tetra cyano HbA+. Over the course of heme saturation with CN?, a certain fraction of the SLTP is specifically released. This shows linkage between organic phosphate binding and heme ligation. These findings bear a marked resemblance to the ligand binding phenomena in hemoglobin A (HbA) and provide good evidence that under these experimental conditions, HbA+ is undergoing a quaternary conformation change as the hemes become saturated. 相似文献
889.
Eugene N. Iheanacho Shalom Sarel Amram Samuni Schelly Avramovici-grisaru Dan T. Spira 《Free radical research》1991,15(1):1-10
Malaria parasites have been shown to be more susceptible to oxidative stress than their host erythro- cytes. In the present work, a chloroquine resistant malaria parasite, Plasmodium falciparum (FCR-3) was found to be susceptible in vitro to a pyridoxal based iron chelator — (l-[N-ethoxycarbonylmethyl- pyridoxlidenium]-2-[2'-pyridyl] hydrazine bromide — (code named L2-9). 2h exposure to 20μM L2-9 was sufficient to irreversibly inhibit parasite growth. Desferrioxamine blocked the drug effect, indicating the requirement for iron. Oxygen however, was not essential. Spectrophotometric analysis showed that under anoxic conditions, L2-9-Fe(II) chelate undergoes an intramolecular redox reaction which presumably involves a one electron transfer and is expected to result in the formation of free radical. Spin trapping coupled to electron spin resonance (ESR) studies of L2-9-iron chelate showed that L2-9-Fe(II) produced free radicals both in the presence and absence of cells, while L2-9-Fe(III) produced free radicals only in the presence of actively metabolising cells. 相似文献
890.
Polarized positive muons are incorporated as spin labels in organic free radicals adsorbed on large-area surfaces. Two muon spin resonance techniques are introduced which allow the detection of the muonanted species, either in transverse or near avoided crossings of energy levels in longitudinal magnetic fields. The radicals are characterized by their hyperfine interactions, and dynamic information is obtained from the extent of averaging of the hyperfine anisotropy. Because of the high spin polarization the method is extremely sensitive and allows the study of radicals at concentrations down to a single radical in the sample at a given time, and therefore under conditions of high mobility where conventional techniques often fail due to radical termination reactions. 相似文献