Phosphatidylcholine spin label

F. 8.24 lipid/peptide titration of the K26 peptide complexes with DMPC obtained from ESR difference spectra of various spin labels 14-PASL phosphatidic acid (o), 14-SASL Stearic acid ( ), 14-PSSL phosphatidylserine (A), 14-PGSL, phosphatidylglycerol ( ), and 14-PCSL phosphatidylcholine ( ) spin labels. The ratio of nP/nb (fluid/restricted) is calculated from the double integrated intensity of the fluid and motionally restricted components in the ESR spectra. The figure is adapted [24] by permission of the American Chemical Society... 

Fig. 3.5. ESR spectra of the cardiolipin spin label 14-CLSL (top row), stearic acid spin label 14-SASL (middle row) and phosphatidylcholine spin label 14-PCSL (bottom row), in ...

Strzalka, K. and W.I. Gruszecki. 1994. Effect of beta-carotene on structural and dynamic properties of model phosphatidylcholine membranes. I. An EPR spin label study. Biochim. Biophys. Acta 1194 138-142. 

Subczynski, W.K., E. Markowska, and J. Sielewiesiuk. 1993. Spin-label studies on phosphatidylcholine-polar carotenoid membranes Effects of alkyl-chain length and unsaturation. Biochim. Biophys. Acta 1150 173-181. 

Fig. 2. Phase diagram describing lateral phase separations in the plane of bilayer membranes for binary mixtures of dielaidoylphosphatidylcholine (DEPC) and dipalmitoyl-phosphatidylcholine (DPPC). The two-phase region (F+S) represents an equilibrium between a homogeneous fluid solution F (La phase) and a solid solution phase S presumably having monoclinic symmetry (P(J. phase) in multilayers. This phase diagram is discussed in Refs. 19, 18, 4. The phase diagram was derived from studies of spin-label binding to the membranes.

Devaux and McConnell9 took advantage of the fact that in fluid membranes such as egg phosphatidylcholine, the resonance spectra of spin labels such as V and VI depend strongly and monotonically on the label concentration c when c 3= 5 mole %. The normalized paramagnetic resonance spectra S0(H, c) of a series of samples, all of uniform concentration c, were determined experimentally.9 The observed time-dependent spectra are then obtained from the equation... 

Devaux and McConnell (39) measured a lateral diffusion coefficient of about 2 X 10"8 cm2/sec at 25°C for phosphatidylcholine (PC) diffusing along bimolecular leaflets in an oriented water-PC lamellar phase. Spin-labeled PC was used in this work. 

Limbacher HP Jr., Blickenstaff GD, Bowen JH, et al. Multiequilibrium binding of a spin-labeled local anesthetic in phosphatidylcholine bilayers. Biochim Biophys Acta 1985 812(l) 268-276. 

Ohtsuru et al. (25) have recently investigated the behavior of phosphatidylcholine in a model system that simulated soy milk. They used spin-labelled phosphatidylcholine (PC ) synthesized from egg lysolecithin and 12-nitroxide stearic acid anhydride. The ESR spectrum of a mixture of PC (250 yg) and native soy protein (20 mg) homogenized in water by sonication resembled that observed for PC alone before sonication. However, when PC (250 yg) was sonicated in the presence of heat-denatured soy protein (20 mg), splitting of the ESR signal occurred. On this basis, they postulated the existence of two phases PC making up a fluid lamella phase and PC immobilized probably due to the hydrophobic interaction with the denatured protein. In a study of a soy-milk model, Ohtsuru et al. (25) reported that a ternary protein-oil-PC complex occurred when the three materials were subjected to sonication under the proper condition. Based on data from the ESR study, a schematic model has been proposed for the reversible formation-deformation of the ternary complex in soy milk (Figure 2). 

BeKsto S, Bartucci R, Montesano G, Marsh D, SporteUi L (2000) Molecular and mesoscopic properties of hydrophilic polymer-grafted phospholipids mixed with phosphatidylcholine in aqueous dispersion interaction of dipalmi-toyl N-poly(ethylene glycol) phosphatidyleth-anolaminewithdipalmitoylphosphatidylcholine studied by spectrophotometry and spin-label electron spin. Biophys J 78 1420-1430... 

The nitroxide (NO) group in spin-labeled phosphatidylcholine gives a distinctive paramagnetic resonance spectrum. This spectrum disappears when nitroxides are converted into amines by reducing agents such as ascorbate. 

Lipid vesicles containing phosphatidylcholine (95%) and the spin-labeled analog (5%) were prepared by sonication and puri-... 

The initial decrease in the amplitude of the paramagnetic resonance spectrum results from the reduction of spin-labeled phosphatidylcholine molecules in the outer leaflet of the bilayer. Ascorbate does not traverse the membrane under these experimental conditions hence, it does not reduce the phospholipids in the inner leaflet. The slow decay of the residual spectrum is due to the reduction of phospholipids that have flipped over to the outer leaflet of the bilayer. 

The spin label technique appeared to be very fruitful recently in research ofmembrane-carotenoids interaction. The shape of a spin probe ESR spectrum is sensitive to the rate of its molecular motion being directly dependent on the membrane fluidity determined by the rate of lipid molecular motion. Thus, the analysis of ESR spectra of spin labels doped into pigmented membranes would provide information on the carotenoid effect on particular regions of lipid bilayers, dependent on the type of probes applied, penetrating different membrane portions. Tfiis technique was applied to study an effect of xanthophylls and j8-carotene on fluidity of lipid membranes formed with several synthetic and nonsaturated phosphatidylcholines (Subczynski et al, 1991,1992,1993 StrzalkaandGruszecki, 1991, Yin and Subczynski, 1996, Wisniewska and... 

Fig. 6. Temperature profiles of peak height (hg) of the central line of 5-SASL ESR spectra in phosphatidylcholine membranes without additions (circles) and containing 10 mol% violaxanthin (crosses). L, M, P, S and B represent DLPC (saturated alkyl chains with 12 carbons), DMPC (14 carbons), DPPC (16 carbons), DSPC (18 carbons) and DBPC (22 carbons), respectively. Arrows indicate the main phase transition temperatures of pure membranes measured using spin-labelling methods. Reproduced from Subczynski et al. (1993) with the permission of Elsevier Science-NL, Sara Burgerhartstraat 25,1055 KV Amsterdam, The Netherlands.

Figure 15. Plot of 1/7 jn vs approximate fatty acyl chain position for egg yolk phosphatidylcholine dispersions labelled within the C5 and spin labels. The l/ term is due to the relaxation mechanism in the presence of the unpaired electron of the nitroxide (taken from Godici and Landsberger, 1974).

Kusumi, A., W.K. Subczynski, M. Pasenkiewicz-Gierula, J.S. Hyde, and H. Merkle. Spin-Label Studies on Phosphatidylcholine-Gholesterol Membranes Effects of Alkyl Ghain Length and Unsaturation in the Fluid Phase, BioohvsActa 854 307-317 (1986). 

The flip-flop of phospholipid molecules in spin-labelled phosphatidylcholine vesicles has been directly measured by electron spin resonance techniques, which show that a phospholipid molecule flip-flops once in several hours, whereas lateral diffusion is 10 times faster. The lateral exchange of bilayer molecules is dependent to some extent on the length of the hydrophobic tails, the extent of head-group hydration, and temperature. 

This approach has been used to study the transfer of spin-labeled phosphatidylcholine mediated by maize protein (Kader, unpublished) or spin-labeled monogalactosyldiacylglycerol facilitated by spinach protein (Nishida and Yaraada, 1986). 

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