Spin labels, phospholipid

This is a fortunate result, since the paramagnetic resonance spectra of phospholipid spin labels such as (V), (VI), (IX), and (X) are sensitive to their state of aggregation, concentration, and rates of lateral motion. This... 

Table 8.1 Resonance data for phospholipid spin labels II (m, n) in Egg-lecitin-cholesterol...

Fig. 8.17 The order parameter Sn for fatty acid spin label I(m,n) in smectic liquid crystals (a), fatty acid spin label I (m,n) (b), and phospholipid spin label II (m,n) (c) in...

Fig. 8.18 The order parameter as a function of n phospholipid spin label II (m,n) in aqueous dispersions of dipalmitoyUecitin (a) 4°C below and (b) 1°C above the transition temperature at 39°C. The figure is adapted from [20] with permission from the American Chemical Society...

The structural and dynamic properties of polymerized surfactant aggregates such as detergent micelles, vesicles and bilayers have been studied extensively (32). From a biological aspect, it is of interest to determine in which way these structures mimic the properties of natural membranes (33). Most luminescent anisotropy studies of lipid rotation have employed the fluorescence characteristics of incorporated probes (34,35), as the time scales of lipid rotation are usually in the ns regime. However, a recent electron spin study using incorporated phospholipid spin-labels (36), indicated that rotation about the long axis of dimyristoyl-phosphatidylcholine (DMPC) lipids below the phase transition occurrs with time constants of about 60-100 is. Such values lie within the time domain of phosphorescence anisotropy measurements. 

A planar BLM cannot be investigated by means of the molecular spectroscopical methods because of the small amount of substance in an individual BLM. This disadvantage is removed for liposomes as they can form quite concentrated suspensions. For example, in the application of electron spin resonance (ESR) a spin-labelled phospholipid is incorporated into the liposome membrane this substance can be a phospholipid with, for example, a 2,2,6,6-tetramethylpiperidyl-A-oxide (TEMPO) group ... 

Gaffney, B.J. and McConnell, H.M. 1974. The paramagnetic resonance spectra of spin labels in phospholipid membranes. Journal of Magnetic Resonance 16 1-28. 

Hubbell, W.L. and McConnell, H.M. 1971. Molecular motion in spin-labeled phospholipids and membranes. Journal of the American Chemical Society 93 314—326. 

A. Chattopadhyay and E. London, Parallax method for direct measurement of membrane penetration depth utilizing fluorescence quenching by spin-labeled phospholipids, Biochemistry 26, 39-45 (1987). 

E. London and G. W. Feigenson, Fluorescence quenching in model membranes. 1. Characterization of quenching caused by a spin-labeled phospholipid, Biochemistry 20, 1932-1938 (1981). 

Lateral diffusion of phospholipids in model membranes at ambient pressure has been studied over the years by a variety of techniques including fluorescence recovery after photobleaching (FRAP), spin-label ESR, pulse field gradient NMR (PFG-NMR), quasielastic neutron scattering (QENS), excimer fluorescence and others.In general, the values reported for the lateral diffusion coefficient (D) range from 10 to 10 cm /s in the... 

NITRENE NITROGENASE NITROGEN FIXATION Nitroxide spin-labeled phospholipids, PHOSPHOLIPID FLIP-FLOP NOISE... 

Seigneuret, M., and Devaus, P. R, ATP-dependent asymmetric distribution of spin-labeled phospholipids in the erythrocyte membrane Relation to shape change. Proc. Natl. Acad. Sci. U.S.A. 81, 3751-3755 (1984). 

The rates of lateral diffusion of phospholipids in lipid bilayer membranes, and in biological membranes, were first measured using spin-labeled lipids.26 50 10 11 9 In general, these rates have been determined by incorporating spin-labeled lipids such as (V) and (VI) in phospholipid bilayers, or multilayers. The paramagnetic resonance spectra of labels such as (V), as well as the nuclear resonance spectra of other lipids in membranes containing (V), depend on the concentration c of the label in the membrane and the rate of lateral motion of the lipids. Two methods... 

Fig. 4. Schematic representation of transient method employed by Devaux and McConnell9 to measure the rates of lateral diffusion of phospholipids in model membranes. The upper diagram represents a concentrated patch of labels at the beginning of the experiment, time f = 0. At later times f>0, the molecules diffuse laterally, as shown in the lower two drawings. The paramagnetic resonance spectra depend on the spin-label concentration in the plane of the membrane, and an analysis of the time dependence of these spectra yielded the diffusion constant. [Reprinted with permission from P. Devaux and H. M. McConnell, J. Am. Chem. Soc., 94, 4475 (1972). Copyright by American Chemical Society.]...

A second steady-state method involves the analysis of the broadening of the nuclear magnetic resonance spectra of phospholipids in bilayers containing low concentrations of spin-labeled phospholipids. A theoretical analysis of the relation between this line broadening and diffusion rates has been given by Brulet and McConnell.3 [In this paper (6) is not correct the subsequent equations are nonetheless correct. For an alternative derivation, see Brulet.2] In this paper it is shown that a number of measurements of nuclear relaxation rates T71 of nuclei in phospholipids are consistent with lateral diffusion constants in the range 10 7 to 10 R cm2/s. 

Fig. 10. Effect of antibody binding on the paramagnetic resonance spectrum of spin-label hapten (X) in phospholipid vesicles.

Spin trapping has also been applied to the investigation of lipid peroxidation catalysed by myoglobin in linoleate emulsions,204 as well as the oxidation of phospholipids in low-density lipoproteins (18.1) by HOC1.205 Hiramoto et al. have shown that, by quenching the attacking radicals, linoleic acid can protect DNA from oxidation.206 Lipid peroxidation has also been monitored by spin labelling.207... 

Zervamicin IIA, a hexadecapeptide antibiotic isolated from fungi, forms ion channels in phospholipid bilayers. When it was spin-labelled at the C-terminal end with tempamine, PELDOR measurements in glassy toluene methanol gave average distances between the spin labels in the aggregates of 25-35 A, depending on solvent composition, which indicated that the peptides oriented in anti-parallel fashion.51... 

This nitroxide is more soluble in liquid regions of bilayers than it is in solid regions. As bilayers are warmed in the EPR spectrometer, the solubility of this spin-labeled compound in the lipid can be followed (see figure). The lower of the three spectra approximates that of the spin label in water alone, while the others are composite spectra for which part of the spin label has dissolved in the phospholipid bilayers. 

There is much evidence, usually based upon ESR studies with spin labels, for conformational changes in the protein during the enzyme cycle. Enzyme activity shows a discontinuity in the Arrhenius plot, once attributed to phase transitions in the membrane phospholipid, but which is similar to discontinuities in the Arrhenius plot for rotational mobility and which have been rationalized in terms of a conformational change in the ATPase.142... 

Fig. 3.17 Change in the order parameter (S ) of spin labels I [3 (7,4) and I [3 (7,8) 1 -stearoyl-2-(10-doxyl) stearoyl-glycero-3-phosphocholine in phospholipid vesicles in the presence of varying amounts of halothane and methoxyflurane.

Lai, C. S., Joseph, J., and Shih, C. C. (1989), Molecular dynamics of antitumor ether-linked phospholipids in model membranes A spin-label study,Biochem. Biophys. Res. Commun., 160,1189-1195. 

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