Dynamic properties of the haptenic site of lipid haptens in phosphatidylcholine membranes. Their relation to the phase transition of the host lattice

The relation between the dynamic properties of the haptenic site of lipid haptens and the phase transition of the host lattice was investigated using head group spin-labeled phosphatidylethanolamines, that is, spin-label lipid haptens (Brûlet, P., and H. M. McConnell, 1976, Proc. Natl. Acad. Sci. USA., 73:2977-2981; Brûlet, P., and H. M. McConnell, 1977, Biochemistry, 16:1209-1217). The electron spin resonance (ESR) spectra of the lipid haptens in liposomal membranes showed three narrow resonance lines, whose widths and hyperfine splitting values suggested that the haptenic site, i.e., the spin-label moiety, should be exposed in the water phase. The line width of each peak depended on the host lipid species and on the incubation temperature. A temperature study using dipalmitoylphosphatidylcholine (DPPC) liposomes showed that the dynamic properties of the haptenic site were related to the main phase transition and the subphase transition of the host lattice but not to the prephase transition. The angular amplitudes of the tumbling motion of the haptenic site were estimated using oriented multibilayer systems. The angular amplitude of dipalmitoyl-phosphatidyl-N-[[N-(1-oxyl-2,2,6, 6-tetramethyl-4-piperidinyl)-carbamoyl]-methyl]-ethanolamine in DPPC membranes was 63 degrees at 2 degrees C, and it increased slightly with an increase in temperature regardless of the phase transition of the host lattice. The value for egg phosphatidylcholine (PC) at 25 degrees C was the same as for DPPC above its main phase transition temperature. Rotational correlation time analysis showed that the axial rotation of the haptenic site was preferable to the tumbling motion of the rotational axis, and the predominance depended on the phase transition, Lc----L beta' and P beta'----L alpha. Elongation of the spacer arm between the haptenic site and phosphate increased the angular amplitude of the tumbling motion but reduced the effect of the host lattice. Spin-label lipid haptens with unsaturated fatty acyl chains were distributed heterogeneously in DPPC membranes, whereas those with the same fatty acyl chain as the host lattice were distributed randomly. The ESR spectrum of a lipid hapten under its prephase transition temperature showed two components, broad and narrow. This suggests that at least two different domains, a hapten-rich domain and a hapten-poor one, may coexist in membranes. ESR measurements at various temperatures suggested that the haptenic site fraction in the hapten-rich domain decreased in part during the phase transition from L beta' to P beta', and disappeared completely in the La phase. The spatial mobility and lateral diffusion of lipid haptens will be discussed in greater detail.

Specific interaction of arabinose residue in ginsenoside with egg phosphatidylcholine vesicles

The interaction of the specific sugar residue in ginsenosides with egg phosphatidylcholine vesicles was investigated by ESR spectrometry using phosphatidic acid spin-labeled at the polar head groups. Ginsenoside-Rc, which has an alpha-L-arabinofuranose residue and agglutinability toward egg yolk phosphatidylcholine vesicles (Fukuda, K. et al. (1985) Biochim. Biophys. Acta 820, 199-206), caused the restriction of the segmental motion of spin-labeled phosphatidic acid in egg phosphatidylcholine vesicles, indicating that the saponin interacted with the polar head groups of vesicles. Other ginsenosides-Rb2, Rb1, Rd and p-nitrophenyl glycoside derivatives which have less or no agglutinability were also investigated in the same manner. Only ginsenoside-Rb2 and p-nitrophenyl alpha-L-arabinofuranoside which have the specific sugar residue (arabinose) showed a strong interaction with the polar head groups of vesicles. To gain an insight into the mechanism of agglutination by ginsenoside-Rc, the interaction with the fatty acyl groups was also studied by using phosphatidylcholine spin-labeled at the fatty acyl groups. Ginsenoside-Rc increased the order parameter of the spin-labeled phosphatidylcholine, indicating that the saponin was inserted into lipid bilayers. In other saponins investigated, only ginsenoside-Rb2 interacted with the fatty acyl part of vesicles. The process of expression of agglutination by ginsenoside-Rc was discussed on the basis of the ESR studies.

Are single or multiple mechanisms involved in radiation-induced mammalian cell killing?

The survival curve of repair-competent mammalian cells exposed to X- or to gamma-rays has a shoulder usually followed by a region of exponential survival. A curve of this shape results from the accumulation of subeffective damage in the shoulder region. This damage has been called sublethal [Elkind & Sutton (1959), Nature, 184, 1293], a designation the basis for which has been questioned by Alper [(1977), Brit. J. Radiol., 50, 459] who noted that if the shoulder results from the progressive reduction of a repair capacity, then the damage would be potentially lethal. A series of experiments is analyzed to show that requiring an equivalence between sublethal and potentially lethal damage has limited usefulness because as many questions are raised as are answered. Moreover, the sector of repair corresponding to the shoulder region is small compared to the sector of damage which must be repaired if only a minority of the lesions in DNA are effective. It is concluded that multiple mechanism may be involved in cell killing and, in addition, that the processes connected with the shoulder region of the survival curve amount to only the tip of an iceberg whose size and properties are yet to be fully appreciated.

Potentially lethal damage, deficient repair in X-ray-sensitive caffeine-responsive Chinese hamster cells

Further studies are described with a radiation-sensitive clone of V79 Chinese hamster cells, designated V79-AL162/S-10. Extended postirradiation treatment with caffeine causes V79-AL162/S-10 cells to respond like repair-competent V79 cells, but both kinds of cells suffer enhanced killing by caffeine, in a similar fashion, when the postirradiation treatment period is relatively brief. Extended postirradiation treatment of repair-competent cells causes them to respond like sensitive cells without caffeine post-treatment. Treating irradiated V79-AL162/S-10 cells with hypertonic saline appreciably reduces the survival rescue which can be effected by caffeine. This latter observation leads to the inference that the sectors of damage affected by anisotonic shock and caffeine post-treatment overlap. From these and other results we propose that the DNA replicational machinery of the cell is the locus of action of these radiation damage/repair processes.

Micellar formation of spin-labeled fatty acyl derivatives of lipophilic muramyl dipeptides and their incorporation into liposomal membranes

A lipophilic muramyl dipeptide (MDP) with a nitroxide moiety in its acyl chain (SL-MDP) and its N-methyl derivative (SL-methyl MDP) were synthesized. The SL-MDPs formed micelles (cmc, 0.1-0.3 mM). The ESR spectra of the SL-MDPs in phosphatidylcholine (PC) liposomes at 25 degrees C consisted of an anisotropic signal and three sharp lines, indicating that both SL-MDPs partitioned between membranes and aqueous phase. The amounts of the SL-MDPs in membranes depended on the phospholipid species and the cholesterol (Chol) content, but no appreciable difference was observed between SL-MDPs. The SL-MDPs partitioned well at 25 degrees C into egg yolk PC liposomes but not into pure dipalmitoylphosphatidylcholine (DPPC), suggesting that the incorporation may be related to the membrane fluidity. Chol enhanced the incorporation into both phospholipids. The mobilities of the SL-MDPs in the membranes were less than that of the corresponding spin-labeled fatty acid. Comparison of the mobilities among SL-MDPs, spin-labeled ganglioside and spin-labeled galactosylceramide showed that the hydrophilicity of the polar group may influence the immobilization of their acyl chains.

Saponins can cause the agglutination of phospholipid vesicles

The interaction of saponins with phospholipid vesicles was investigated by means of liposomal agglutination or a precipitation assay. Ginsenoside-Rc, which has an alpha-L-arabinofuranose residue at the non-reducing terminus, exhibited remarkable agglutinability toward egg yolk phosphatidylcholine vesicles, while other saponins lacking this characteristic sugar residue showed less or no agglutinability. The molar ratio of ginsenoside-Rc to egg phosphatidylcholine in the aggregates was estimated to be 0.4-0.5 by a precipitation assay using 14C-labeled egg phosphatidylcholine vesicles. The agglutination was inhibited by p-nitrophenyl alpha-L-arabinofuranoside but not by p-nitrophenyl beta-D-glucopyranoside or arabinogalactan. The results indicated that the alpha-L-arabinofuranose residue in ginsenoside-Rc should be important for the expression of the agglutinability. The agglutinability of ginsenoside-Rc toward lipid vesicles depended on both the polar head groups and fatty acyl chains of phospholipids. Egg yolk phosphatidylcholine vesicles were strongly agglutinated by ginsenoside-Rc, although sphingomyelin, phosphatidylethanolamine, phosphatidic acid and phosphatidylserine were less agglutinated. The agglutinability of ginsenoside-Rc was effective for phosphatidylcholines with short or unsaturated fatty acyl chains. The results suggested that the interaction of ginsenoside-Rc with phospholipid membranes should be affected not only by the chemical structure of the phospholipid but also by the membrane fluidity.

Two forms of potentially lethal damage have similar repair kinetics in plateau- and in log-phase cells

The effect on the survival of X-irradiated Chinese hamster cells (line V79) of two different post-treatments is examined in plateau- and in log-phases of growth. Qualitatively similar results are obtained with cells in both growth phases; that is, similar reductions in survival are effected by post-treatments with hypertonic phosphate buffered saline, and similar increases in survival are effected by post-treatments with conditioned medium. In addition, in both kinds of cells the kinetics of the repair processes are similar even though the kinetics of the two processes differ from each other considerably. While the results indicate that there can be essential differences in the type and/or the pathways of repair of potentially lethal damage, they also illustrate a broader meaning of this term than has been customary. Considered relative to the amount of DNA damage that can be expected to be potentially lethal, it is concluded that the two types of damage that are the subjects of this study represent only small sectors of the total amount of potentially lethal damage.

Structural changes of rat liver microsomal membranes induced by the oral administration of carbon tetrachloride. 31P-NMR and spin-label studies

The acute effects of carbon tetrachloride (CCl4) on the membrane structure of rat liver microsomes were studied using 31P-NMR and spin-labeling techniques. 31P-NMR spectra of rat liver microsomes were not changed appreciably after the oral administration of CCl4, indicating that the surface structures of microsomal membranes probably are not influenced by the oral administration of CCl4. Four different spin-labeled stearic acids, 5-(N-oxyl-4',4'-dimethyloxazolidine)-stearic acid (5SLS), its methyl ester (5SLSM), 12-(N-oxyl-4',4'-dimethyloxazolidine)-stearic acid (12SLS) and its methyl ester (12SLSM), were used for the estimation of membrane fluidity. The apparent rotational correlation time of 12SLS decreased from 4.0 nsec to 3.0 nsec after the oral administration of CCl4, while the order parameter of 5SLS did not change. The results suggest that CCl4 or its metabolites increase the membrane fluidity of liver microsomes primarily at hydrophobic regions rather than at the surface layer. The ESR spectrum of 5SLSM in microsomal membranes comprised two different signals; one was an anisotropic signal and the other was a rather isotropic one. The ratio of the anisotropic signal to the isotropic one decreased markedly after the oral administration of CCl4 and depended on the dose of CCl4. The suitability of this ESR technique with 5SLSM for the estimation of membrane damage is discussed.

Haptenic activity of galactosyl ceramide and its topographical distribution on liposomal membranes. Effects of temperature and phospholipid composition

The relation between the immune reactions of phosphatidylcholine liposomes containing galactosyl ceramide and the physical properties of the glycolipid in membranes was studied. The immune-agglutination of dipalmitoyl phosphatidylcholine liposomes was affected both by reaction temperature and by cholesterol content. Fatty acyl chain length of phosphatidylcholine also influenced the immune-agglutination. The electron spin resonance and calorimetric studies indicated that the fatty acyl chain length of phosphatidylcholine and cholesterol content, as well as temperature, affect the physical properties of galactosyl ceramide in liposomal membranes. In the absence of cholesterol, most galactosyl ceramide molecules were clustered on the phosphatidylcholine liposomes below the chain-melting transition temperature of the phospholipid, whereas they were randomly distributed in the membrane above the transition temperature. Upon addition of cholesterol to the membranes below the chain-melting transition temperature, the number of glycolipid molecules in the cluster phase decreased. Cholesterol increased the ordering of galactosyl ceramide molecules in the phase of random distribution on membranes above the transition temperature. The change in topographical distribution of galactosyl ceramide in membranes was parallel with that of immune-reactivity.

Inhibitors of poly(ADP-ribose) synthesis enhance X-ray killing of log-phase Chinese hamster cells

Postirradiation incubation of V79 Chinese hamster cells with inhibitors of poly(ADP-ribose) synthesis was found to potentiate the killing of cells by X rays. Potentiation increased with incubation time and with concentration of the inhibitor. Preirradiation incubation had only a small effect. The enhanced response correlated well with the known extent of the inhibition of poly(ADP-ribose) synthesis. A radiation-sensitive line, V79- AL162 /S-10, was affected to a lesser extent than the normal cells. Cells repaired the radiation damage with which the inhibitors interacted within 1 hr, a process that has similar kinetics to what is observed when a postirradiation treatment with hypertonic buffer is used [H. Utsumi and M. M. Elkind , Radiat . Res. 77, 346-360 (1979)]. However, the sectors of damage affected by inhibitors of poly(ADP-ribose) synthesis and hypertonic buffer do not entirely overlap. The inhibitor nicotinamide enhanced the killing mainly of late S-phase cells and did not affect cells at the G1/S border. It is concluded that the repair process(es) involving poly(ADP-ribose) synthesis is important for cell survival in repair-competent cells and that the radiation-sensitive cells that were examined are partially deficient in a repair pathway in which poly(ADP-ribose) participates.

Deficient repair of potentially lethal damage in actively growing ataxia telangiectasia cells

The repair of potentially lethal damage after X rays was studied in exponentially growing normal and ataxia telangiectasia (A-T) strains of human fibroblasts. X-ray killing of all normal strains from six healthy persons was enhanced when cells were treated with treated with hypertonic phosphate-buffered saline immediately after irradiation. This treatment is not toxic to unirradiated cells and demonstrates that ordinarily these cells repair potentially lethal damage. The potentially lethal damage in normal cells is repaired within 1 hr. These data with normal human fibroblasts are similar to and consistent with those obtained with V79 Chinese hamster cells [H. Utsumi and M. M. Elkind, Radiat. Res. 77, 346-360 (1979)]. In contrast, all A-T strains from four A-T patients were completely deficient in their ability to repair potentially lethal damage. Treatment with a hypertonic solution after X irradiation is known to increase the frequency of chromosomal aberrations and to enhance cell killing, as though hypertonicity had induced the A-T state in normal cells. Recently, the effects of hypertonicity on DNA synthesis in X-irradiated normal and A-T cells were reported to be similar [R.B. Painter and B.R. Young, Radiat. Res. 92, 552-559 (1982)]. These results support the inference that the increased radiosensitivity of A-T cells can be attributed to some defect in the repair of DNA damage rather than abnormal DNA synthesis following irradiation.

Inhibitors of poly (ADP-ribose) synthesis enhance radiation response by differentially affecting repair of potentially lethal versus sublethal damage

The effect of nicotinamide and m-aminobenzamide, representative inhibitors of poly(ADP-ribose) synthesis, on the survival of V79 Chinese hamster cells following ionizing radiation was studied in plateau- and log-phase cultures. In plateau-phase, after an acute dose of X-rays, nicotinamide partially inhibited the repair of potentially lethal damage that occurs when the plating of such cells is delayed. The incompleteness of the inhibition was attributed to the slowness of the uptake of nicotinamide by unfed plateau-phase cells. Postirradiation incubation of log-phase cells with either of these inhibitors caused a pronounced enhancement of the radiation response which was reflected mainly by a reduction of the shoulder on the survival curve. However, the ability of such treated cells to repair sublethal damage was hardly affected as demonstrated by the reappearance of the shouldered survival curve during a fractionation interval. NAD levels in irradiated cells were rapidly reduced. This reduction was somewhat slower in a radiation sensitive mutant and was almost completely blocked in the presence of m-aminobenzamide. Another treatment that enhances the radiation response, i.e., incubation in D2O medium, facilitated the rate of NAD depletion in irradiated cells. We conclude that inhibitors of poly(ADP-ribose) synthesis inhibit the repair of potentially lethal damage in plateau-phase as well as in log-phase cells with little if any effect on the repair of sublethal damage. Poly(ADP-ribose) appears, therefore, to have a role in the repair of radiation damage that is potentially lethal in mammalian cells.

Partial inhibitory seizures: a report on two cases

This paper described two epileptic children with the clinical features of tonic-clonic seizures, brief atonic episodes, drop attacks and myoclonic jerks. Patient 2 also displayed absences and behavioral disturbance with episodes of minor status epilepticus. When the patients held both arms outstretched, polygraphic records revealed the spike-and-wave (sp-w) discharges in association with the sudden dropping of an outstretched arm. The drops were due to a loss of tone recorded in deltoid muscles, and coincided with the slow wave components of bilateral sp-w complexes, predominantly on the contralateral side. In the present paper, the clinical and electrophysiologic features of this particular type of seizure are presented in detail. A cortical origin of these episodes is suggested.

Caffeine-enhanced survival of radiation-sensitive, repair-deficient Chinese hamster cells

A clone of V79 Chinese hamster cells (V79-AL162/S-10) with unique properties has been isolated after a challenge of parental cells (V79-AL162) with 1 mM ouabain. Compared with parental cells, or with other clones isolated after the ouabain challenge, these cells form smaller colonies, are more sensitive to both X rays and fission-spectrum neutrons, and respond atypically to a postirradiation treatment with caffeine. Their enhanced response to X rays results mainly from a large reduction in the shoulder of their survival curve, probably because in late S phase, the most resistant phase in the cell cycle, the survival curve of these cells has a reduced shoulder width. Caffeine, and to a lesser extent theophylline, added to the colony-forming medium immediately after exposure appreciably increases the width of the shoulder of these sensitive cells, whereas caffeine has the opposite effect on the response of normal V79 cells. Because dibutyryl-cAMP added immediately after exposure actually further sensitizes these sensitive cells, it would appear that the enhanced survival due to methylxanthines, which inhibit cAMP phosphodiesterase, does not result from increases in intracellular levels of cAMP. Thus the unique response of the V79-AL162/S-10 cells to a radiation posttreatment with caffeine (increased survival) results from a net increase in their ability to repair damage that is otherwise lethal; caffeine treatment ordinarily prevents normal V79 cells from repairing damage that is only potentially lethal.

Ipsilateral disturbance of taste due to pontine haemorrhage

A patient with haemorrhage in the right tegmentum of the pons demonstrated ipsilateral disturbance of taste on both the anterior two-thirds and posterior one-third of the tongue. The contralateral medial lemniscus was not disturbed, contrary to the early descriptions that the secondary gustatory neurons from the nucleus of the solitary tract cross and turn upwards in the pons through the contralateral medial lemniscus. This finding would accord with the concept of the pontine taste area which receives ipsilaterally the secondary gustatory neurons from the anterior pole of the nucleus of the solitary tract.

Orientation of platelets on the surfaces of glass and Teflon plates as studied by a spin label technique

Platelets were found by a spin label technique to orient on flat surfaces of glass as well as of Teflon. This kind of platelet orientation was not caused by centrifugation or partial dehydration of the membrane preparation as employed usually to make oriented planar multilayers of biological membranes on the surface of a supporting plate (1-8), but was considered to be closely related to the adhesion or the aggregation properties of platelets. The amount of oriented platelets varied depending on the platelet treatment and was estimated from a computer simulation of the observed ESR spectra to be about one-half of that of the non-oriented ones in the case of thrombin-treated platelets. This technique may be useful as a new tool to explore the adhesion or aggregation properties of platelets.

Incorporation of a ganglioside and spin-labeled ganglioside analogue into cell and liposomal membranes

When an aqueous solution of a spin-labeled "two tail" gangliosidoid was incubated with liposomes or sheep erythrocytes, the broad single resonance line in the ESR spectrum disappeared and a signal showing an anisotropic motion appeared, indicating that the spin-labeled "two tail" gangliosidoid in the micellar state was transferred to the lipid phase of the acceptor membranes. The transfer was temperature- and time-dependent, irrespective of the acceptor membranes, indicating that the rate of transfer is determined by the escape of monomers from the micelles. The kinetics and temperature-dependence of the association of ganglioside II3NeuAc-GgOse4Cer with sheep erythrocytes was very similar to that of the "two tail" gangliosidoid, indicating that parts of ganglioside II3NeuAc-GgOse4Cer could be incorporated into the lipid phase of membranes via a similar mechanism.

Incorporation of spin-labeled ganglioside analogues into cell and liposomal membranes

Ganglioside analogues (gangliosides) with an electron spin resonance label in a long aliphatic hydrocarbon chain were used to investigate the possible insertion of the sialoglycolipid into the plasma membrane of cells. Three types of ESR signals observed in the labeled glycolipids were distinguished. They characteristically indicate an isotropic tumbling motion of spin label in solution, the micellar state of the glycolipid, and an anisotropic motion in a lipid bilayer. Below CMC, gangliosidoide carrying one aliphatic hydrocarbon chain showed an isotropic tumbling motion. After the gangliosidoide had been incubated with liposomes or blood cells, there was an immediate change to an ESR signal showing an anisotropic motion. The signal was typical of the spin-label in liposomes prepared in the presence of spin-labeled sialoglycolipid. It can be concluded that the gangliosidoide was inserted into the lipid phase of liposomal or cellular membranes from the incubation medium. The overall splitting (2A parallel) of 5SL-gangliosidoides in membranes was larger than those of 5SL-galactosylceramide, 5SL-phosphatidylcholine, and 5SL-stearic acid, though the 2A parallel of 12SL-gangliosidoide was almost the same as those of other lipids having a nitroxide group in the 12-position of an acyl chain. This indicates that the head group movement is restricted in gangliosidoide molecules.

Radiosensitivity of fibroblasts from patients with retinoblastoma and chromosome-13 anomalies

Diploid fibroblast cell strains derived from 14 patients with various forms of retinoblastoma (RB) and 5 non-RB patients with constitutional chromosome anomalies involving chromosome 13 were assayed for their clonogenic survival after X-irradiation. Cells from a patient with ataxia telangiectasia (AT) was used as a radiosensitive reference strain. When compared with cell strains from 7 healthy persons as normal controls, a marked radiosensitivity was observed in strain from an AT patient. However, none of the cell strains derived from RB patients or patients with inborn anomalies in chromosome 13 showed pronounced deviation from the normal range of radiosensitivity. The findings thus did not warrant either the RB as radiosensitive genetic disease or the presence of repair locus on chromosome 13, deletion or triplication of which was previously suggested to link to radiosensitivity.

Spectral dependencies of killing, mutation, and transformation in mammalian cells and their relevance to hazards caused by solar ultraviolet radiation

Using germicidal lamps and Westinghouse sunlamps with and without filtration, the effectiveness of ultraviolet and near-ultraviolet light in inducing molecular and cellular changes was measured. Cell survival and the induction of resistance to 6-thioguanine or to ouabain were measured with V79 Chinese hamster cells, cell survival and neoplastic transformation were measured with C3H mouse 10 T 1/2 cells, and the induction of pyrimidine dimers containing thymine was measured in both cell lines. The short-wavelength cutoff of the sunlamp emission was shifted from approximately 290 nm (unfiltered) to approximately 300 and approximately 310 nm by appropriate filters. Although it was found that the efficiency with which all end points were induced progressively decreased as the short-wavelength cutoff was shifted to longer wavelengths, the rates of decrease differed appreciably. For example, doses of near-ultraviolet light longer than approximately 300 nm that were effective in mutating or in transforming cells were ineffective in killing them. In respect to pyrimidine dimer induction, several but not all cellular end points were induced by dose ratios of sunlamp light (short-wavelength cutoff, approximately 290 nm) to germicidal lamp light (254 nm) in fairly close accord with the doses required to produce equivalent proportions of dimers. However, for near-ultraviolet light having cutoffs at longer wavelengths, the biological action observed was appreciably greater than what would be predicted from the proportion of dimers induced. From the latter observation, it is inferred that increasing intensities of short-wavelength ultraviolet light, as would be expected from reductions in stratospheric ozone around the earth, would result in smaller increases in biological action, e.g., skin cancer, compared to current levels of action than would be predicted from an action spectrum completely corresponding to that of a pyrimidine dimer induction spectrum in DNA.

Haptenic activity of galactosyl ceramide and its topographical distribution on liposomal membranes. I. Effect of cholesterol incorporation

The relation between the immune-reaction of phosphatidylcholine liposomes containing spin-labeled galactosyl ceramide with or without cholesterol and the topographical distribution of the glycolipid in membranes was studied. In egg yolk phosphatidylcholine liposomes, both immune agglutination and antibody binding occurred, irrespectively of the presence of cholesterol, though the motion of the fatty acyl chain of spin-labeled galactosyl ceramide was restricted by cholesterol. In dipalmitoyl phosphatidylcholine liposomes, unlike in egg yolk phosphatidylcholine liposomes, the immune-reaction depended on the cholesterol content. The electron spin resonance (ESR) spectra of spin-labeled galactosyl ceramide in dipalmitoyl phosphatidylcholine liposomes indicated that cholesterol affected the topographical distribution of spin-labeled galactosyl ceramide in the liposomes. Without cholesterol, most of the spin-labeled galactosyl ceramide was clustered on the dipalmitoyl phosphatidylcholine membrane, but with increase of cholesterol, random distribution of hapten on the membrane increased. The cholesterol-dependent change in the topographical distribution of hapten on the membranes was parallel with that of immune reactivity. 'Aggregates' composed solely of galactosyl ceramide did not show any binding activity with antibody. The findings suggest that the recognition of galactosyl ceramide by antibody depended on the topographical distribution of hapten molecules. Phosphatidylcholine and/or cholesterol may play roles as 'spacers' for the proper distribution of 'active' haptens on the membranes. The optimum density of haptens properly distributed on liposomal membranes is discussed.

Carbon-13 nuclear magnetic resonance studies on the interaction of glycophorin with lecithin in reconstituted vesicles

Glycophorin, the MN blood group substance, is a major intrinsic glycoprotein in erythrocyte membranes. The interaction of glycophorin with phosphatidylcholine, 13C-labeled in specific positions in reconstituted unilamellar vesicles, was investigated by using the 13C NMR technique. 1-Palmitoyl-2-([14-13C]linoleoyl)-sn-glycero-3-phosphocholine was synthesized and used as a probe. At 37 degrees C the spin-lattice relaxation time (T1) of vesicle bilayers consisting of this phospholipid was 0.74 s in the absence of glycophorin. The incorporation of glycophorin decreased the T1 to 0.63 s, indicating that the bulk lipid molecules are somewhat immobilized by glycophorin. In addition to the reduction in time, a broad component (delta H1/2 = approximately 40 Hz) superimposing the sharp resonance was observed in the 13C NMR spectrum of reconstituted vesicles. The T1 of the broad component was 0.32 s, suggesting that the lipid molecules contributing to the broad component may be more restricted than that of the sharp component. In order to quantify the broad component, a computer simulation was performed. The intensity of the broad component estimated from the simulation depended linearly on the concentration of glycophorin. Therefore, the broad component is considered to be contributed by a phospholipid domain surrounding the glycophorin molecules, a so-called "boundary lipid". The relationship between the broad component and the stoichiometry of the reconstituted vesicles allows the conclusion that about 30 lipid molecules are immobilized by one glycophorin monomer.

Transfer of cholestane spin label between lipid bilayer membranes and its molecular motion in membranes

The relation between the molecular motion of a steroid in lipid membranes and the transfer rate between membranes was examined using radioactive cholestane spin label. Order parameters of the molecule were determined in bilayers composedof dipalmitoylglycerophosphocholine or egg yolk phosphatidylcholine at various temperatures. The line widths of the ESR signal of the cholestane spin label in membranes, which depend upon the rate of molecular axial rotation in the membranes, were also measured. The temperature dependences of these two parameters and of the transfer rate suggest a close correlation between the rate of molecular axial rotation and the transfer rate.

Synthesis and micellar formation of spin-labeled lysolecithin

A spin-labeled lysolecithin, 1-[12'-(N-oxyl-4",4"-dimethyloxazolidine)-stearoyl]-sn-glycero-3-phosphorylcholine, has been synthesized in which the spin is covalently attached to its fatty acyl chain. The electron spin resonance spectra of this lysolecithin is an aqueous solution generally showed sharp three resonance lines superposed on a broad resonance line. Investigation of changes in the signal intensity of these spectra against the concentration of lysolecithin led to the inference that the sharp lines are due to monomers of lysolecithin while the broad one to micelles. The critical micellar concentration was consistent with that evaluated from the spectral shift of a dye. In the electron spin resonance spectra obtained from spin-labeled lysolecithin solutions with various amounts of dimyristoyllecithin, the line width of broad signal arised from micellar spin-labeled lysolecithin broadened as increase of dimyristoyllecithin. The line-broadening thus observed was briefly discussed.