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PubMed1987

Phase separation and hexagonal HII phase formation by gramicidins A, B and C in dioleoylphosphatidylcholine model membranes. A study on the role of the tryptophan residues.

The role of the tryptophan-residues in gramicidin-induced HII phase formation was investigated in dioleoylphosphatidylcholine (DOPC) model membranes. 31P-NMR and small angle X-ray diffraction measurements showed, that gramicidin A and C (in which tryptophan-11 is replaced by tyrosine) induce a similar extent of HII phase formation, whereas for gramicidin B and synthetic analogs in which one tryptophan, either at position 9 or 11 is replaced by phenylalanine, a dramatic decrease of the HII phase inducing activity can be observed. Modification of all four tryptophans by means of formylation of the indole NH group leads to a complete block of HII phase formation. Sucrose density centrifugation experiments on the various peptide/lipid samples showed a quantitative incorporation of the peptide into the lipid. For all samples in a 1/10 molar ratio of peptide to lipid distinct bands were found, indicative of a phase separation. For the gramicidin A'/DOPC mixture these bands were analyzed and the macroscopic organization was determined by 31P-NMR and small-angle X-ray diffraction. The results demonstrate that a quantitative phase separation had occurred between a lamellar phase with a gramicidin/lipid ratio of 1/15 and a hexagonal HII phase, which is highly enriched in gramicidin. A study on the hydration properties of tryptophan-N-formylated gramicidin in mixtures with DOPC showed that this analog has a similar dehydrating effect on the lipid headgroup as the unmodified gramicidin. In addition both the hydration study and sucrose density centrifugation experiments showed that, like gramicidin also its analogs have a tendency to aggregate, but with differences in aggregation behaviour which seemed related to their HII phase inducing activity. It is proposed that the main driving force for HII phase formation is the tendency of gramicidin molecules to self-associate and organize into tubular structures such as found in the HII phase and that whether gramicidin (analogs) form these or other types of aggregates depends on their tertiary structure, which is determined by intra- as well as intermolecular aromatic-aromatic stacking interactions.

Gramicidin↗

PubMed1988

Cell cycle phase-specific cDNA libraries reflecting phase-specific gene expression of Ehrlich ascites cells growing in vivo.

Asynchronous populations of Ehrlich ascites tumor cells grown in vivo were separated by centrifugal elutriation into fractions of G1-, S-, and G2/M-phase cells with less than 10% cross-contamination. Cytoplasmic mRNA from phase-synchronous cells was used to prepare cDNA which was ligated with bacteriophage lambda gt10 arms and amplified in Escherichia coli C600 hfl-. EcoRI digests of DNA isolated from the sublibraries (G1, S, G2/M) were submitted to Southern hybridizations with radiolabeled probes either (a) for genes whose phase-specific expression is clearly documented, thymidine kinase, dihydrofolate reductase, and thymidylate synthase, or (b) for genes whose change of expression during the cell cycle is likely, lamin C, beta-actin, alpha- and beta-tubulin, c-myc, c-fos, p53. The cDNA sequences for genes of group (a) were found to be significantly enriched in DNA of the S-phase library indicating that the cell cycle phase-specific patterns of the respective mRNA levels are conserved in the sublibraries. Sequences belonging to group (b) were also found to be enriched in DNA isolated from the sublibraries: c-fos in G1 phase, lamin C, beta-actin, tubulins, c-myc in S phase, and p53 in G1/S phase. The unexpected prevalence of c-myc and alpha-tubulin in the S-phase library is supported by Northern analysis of RNA from phase-synchronous cells. Non-phase-specific, randomly chosen sequences hybridized equally strong with DNA isolated from the different sublibraries. No significant changes of the patterns of hybridization signals were observed with DNA from different amplifications of the sublibraries when analyzed with the same DNA probe indicating that the cDNA complexities are well conserved during amplifications. Consequently, the sublibraries are useful to obtain information about the cell cycle phase-specific expression of mRNAs for other genes of interest. Since the sublibraries reflect mRNA levels of the cells growing in vivo they supply data on the physiological in vivo pattern of gene expression undisturbed by potentially unphysiological in vitro conditions.

Animals↗

PubMed1992

Cubic phases of lipid-containing systems. The structure of phase Q223 (space group Pm3n). An X-ray scattering study.

The hexagonal (H) and the cubic (Q223) phases of the systems dodecyltrimethylammonium chloride-water and palmitoyllysophosphatidy choline-water have been studied by X-ray scattering techniques. The signs of the reflections of phase H were determined by a systematic study as a function of the water content, those of phase Q223 were assessed using a pattern recognition approach based upon the axiom that the histograms of the electron density maps of phases Q223 and H, extrapolated to the same concentration and properly normalized in scale and shape, are very similar to each other. In the case of phase Q223, all the sign combinations (the phi-sets) compatible with the observed reflections were generated, and each of the corresponding histograms was compared with the histogram of the map of phase H. One novelty of this work is the use of a highly sensitive criterion to estimate the similarity of the histograms, namely the distance in the six-dimensional space of the moments [mean value of (delta rho)n]1/n, for 3 greater than or equal to n greater than or equal to 8. In the two systems, the use of this criterion has led to the unambiguous choice of one electron density map. The maps show that the structure of phase Q223 consists of disjointed micelles (of type I), belonging to two different classes: those of one class are quasi-spherical in shape and are centered at the points a, those of the other class are disc-shaped and are centred at the points c. The results of this work rule out a structure formed by a cage-like distribution of rods enclosing a set of quasi-spherical micelles and is consistent with previous proposals. This is the second example, after that of phase Q227, of a micellar cubic phases in lipid-containing systems; all the known examples of phase Q223 are of type I, those of phase Q227 of type II.

Freeze Fracturing↗

PubMed1981

Fate of phase I and phase II Coxiella burnetii in several macrophage-like tumor cell lines.

Several macrophage-like tumor cell lines of murine origin were exposed to phase I and phase II Coxiella burnetii, and the subsequent fate of the parasites was determined by electron and bright-field microscopy. Phase I C. burnetii proliferated within and established a persistent infection of P388D1, J774, and PU-5-IR cell lines but not of WEHI-3 and WEHI-274 cell lines. Phase II C. burnetii, however, entered into and persistently infected all five cell lines. The parasites proliferated within vacuoles. Macrophage cell lines persistently infected with phase I and phase II C. burnetii were maintained for over 200 and 100 days, respectively. Within P388D1 cells, the phase I C. burnetii converted, in part, to phase II; phase II organisms remained in the phase II state. The differential fate of the two rickettsial phases after exposure to the WEHI-3 and WEHI-274 cells may be attributable to surface differences such as lipopolysaccharide content.

Animals↗

PubMed1992

Biomechanical properties of duodenal wall and duodenal tone during phase I and phase II of the MMC.

We used a new method, impedance planimetry, to look at variations in compliance, tone, and distension-induced peristaltic activity during phase I and phase II of the migrating myoelectric complex (MMC) in the human duodenum. A balloon was inflated stepwise with pressures up to 30 cmH2O in the duodenum, while the pressure and balloon cross-sectional area (CSA) were measured simultaneously. The biomechanical wall parameters were calculated from these measurements. Nine duodenal phase IIIs were recorded in six subjects. A balloon pressure of 20 cmH2O induced a smaller CSA in early phase I [266 (236-324) mm2] than in late phase II [385 (276-474) mm2] (P < 0.05). Balloon distensions elicited no contractions in phase I, whereas they increased contractile activity 60% (P < 0.05) proximal to the balloon and 4% distal to the balloon in late phase II. Step distensions in phase I with balloon pressures between 10 and 30 cmH2O increased the CSA from 40 (30-81) to 645 (603-704) mm2. It increased circumferential wall tension from 35 (28-63) to 429 (402-466) mm x cmH2O and the pressure elastic modulus from 9.7 (9.0-14.7) to 33.8 (27.6-33.8) cmH2O, respectively. Thus compliance differs from phase I to phase II. This is most likely caused by increased smooth muscle tone during phase I. Duodenal wall stiffness increases with the balloon pressure applied.

Adult↗

PubMed1990

Signal-to-noise in phase angle reconstruction: dynamic range extension using phase reference offsets.

The dynamic range of phase-reconstructed magnetic resonance images is compared to that of magnitude-reconstructed images. From analysis of propagation of errors, the phase angle noise is phase-independent and given in radians by sigma ([I])/[I], the noise-to-signal ratio of the corresponding magnitude-reconstructed image. As the phase can range from minus pi to pi, the phase angle dynamic range is 2 pi times that of the signal magnitude. These results agree with experiment, verifying that the noise in the two receiver channels is uncorrelated. An artifact-free technique is presented for correcting phase spillover, which further extends the phase angle dynamic range. The reconstruction-based reference phase is adjusted on a local basis so that the boundary of phase wraparound is reconstructed near the center of the [- pi, pi] interval. For a particular flow study, the phase signal-to-noise was extended over twofold by spillover correction, to a value 15 times that of the magnitude signal-to-noise.

Algorithms↗

PubMed1983

A low-temperature structural phase transition of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine bilayers in the gel phase.

A new thermotropic phase transition, at -30 degrees C and atmospheric pressure, was found to occur in the gel phase of aqueous DPPC dispersions. The Raman spectral changes at this phase transition are similar to those observed in the gel phase of DMPC dispersions at -60 degrees C. The thermotropic phase transition at -30 degrees C is equivalent to the barotropic GII to GIII phase transition observed in DPPC at 1.7 kbar and 30 degrees C. It is shown that the rate of the large angle interchain reorientational fluctuations decreases gradually with decreasing temperature, and that the orientationally disordered acyl chain structure of the GII phase is extended into the GIII phase of DPPC. The interchain interaction, arising from the damping of the reorientational fluctuations, increases with decreasing temperature in the GII gel phase as well as in the GIII gel phase.

Dimyristoylphosphatidylcholine↗

PubMed1985

Phase transitions and fatty acid spin label behavior in interdigitated lipid phases induced by glycerol and polymyxin.

Glycerol and polymyxin have been shown by X-ray diffraction to induce interdigitated bilayers in phosphatidylcholine (PC) and phosphatidylglycerol (PG), respectively (McDaniel, R.V., et al. (1983) Biochim. Biophys. Acta 731, 97-108; Ranck, J.-L. and Tocanne, J.-F. (1982) FEBS Lett. 143, 175-178). In the present study we have investigated the phase behavior of PC and PG in the presence of glycerol and polymyxin by differential scanning calorimetry and the use of fatty acid spin labels. Interdigitation causes a large increase in the order parameter of a fatty acid spin labeled near the terminal methyl, 16-doxylstearate, so that it was similar to that of a fatty acid labeled much closer to the polar head group region, 5-doxylstearate. Thus interdigitation abolishes the fluidity gradient found in a non-interdigitated bilayer. 16-Doxylstearate may be useful in detecting interdigitation of lipid bilayers caused by other substances. The different samples all went through two transitions on heating or cooling, or both. However, use of the fatty acid spin label showed that the molecular events during these transitions varies for different samples. The results suggested that PC-glycerol freezes from the liquid-crystalline phase into a non-interdigitated gel phase. This subsequently becomes interdigitated upon lowering the temperature a few degrees, in a low enthalpy transition. PG-polymyxin shows a similar behavior except that the enthalpy of the non-interdigitated gel to interdigitated phase transition is greater and the transition is reversible on heating. Thus on heating PG-polymyxin first goes through a transition from the interdigitated phase to a non-interdigitated gel phase and then, in a separate transition, to the liquid-crystalline phase. This occurs because the fatty acid chains in the presence of polymyxin become too disordered with increase in temperature to maintain the interdigitated state. PG-glycerol goes into the interdigitated state less readily than the other mixtures. If cooled rapidly, PG-glycerol freezes into a metastable phase which is more disordered than the interdigitated phase. It goes into the interdigitated phase in an exothermic transition on heating. An increase in fatty acid chain length causes greater steric hindrance to interdigitation but also increases the stabilizing energy gained by interdigitation.

Calorimetry, Differential Scanning↗

PubMed1985

Phase 1 and Phase 2 drug metabolism in isolated epidermal cells from adult hairless mice and in whole human hair follicles.

A sensitive fluorimetric assay to determine both Phase 1 (oxidation) and Phase 2 (conjugation) drug metabolism in epidermal cells isolated from hairless mice, using ethoxycoumarin as a model substrate, is described. Ethoxycoumarin was metabolized by isolated epidermal cells via dealkylation to 7-hydroxycoumarin (7-OHC) and subsequent conjugation. Phase 1 metabolites were extracted in ether from the aqueous incubation media, back extracted into sodium hydroxide and determined fluorimetrically. Conjugated metabolites remaining in the aqueous phase were hydrolysed by the action of beta-glucuronidase and extracted and determined in a similar manner. The production of free 7-OHC by isolated epidermal cells was biphasic at all substrate concentrations tested, exhibiting an initial linear increase followed by a plateau phase. The plateau phase was attributable to the conjugation of 7-OHC produced in situ. Metabolism was inhibited by SKF 525A, carbon monoxide, and alpha-naphthoflavone. Endogenous supplies of reducing equivalents in the form of NADPH were adequate to attain maximal rates of metabolism. With human hair follicles both Phase 1 and Phase 2 activity was detectable in 7 out of 11 subjects. The assay has the advantages of being sensitive, producing single defined metabolites from both Phase 1 and Phase 2 metabolism; is readily adaptable to human skin samples.

Animals↗

PubMed1986

Inverted micellar intermediates and the transitions between lamellar, cubic, and inverted hexagonal amphiphile phases. III. Isotropic and inverted cubic state formation via intermediates in transitions between L alpha and HII phases.

Inverted cubic and isotropic phases have been observed in phospholipid and glycolipid systems. These phases exhibit characteristic morphologies in freeze-fracture electron micrographs, isotropic 31P-NMR resonances and (in some cases) cubic X-ray diffraction patterns. It is proposed here that these phases may form from the same intermediates that are involved in lamellar/inverted hexagonal (L alpha/HII) phase transitions, and that it is possible that these cubic and isotropic phases are metastable. According to a kinetic theory of L alpha/HII phase transitions, intermediates in such transitions can form structures known as interlamellar attachments (ILAs). It is shown that ILAs should form in large numbers during L alpha/HII transitions in systems like those reported to form inverted cubic or isotropic structures. ILAs cannot readily assemble into either the HII phase or well-ordered arrays of L alpha phase bilayers, and represent a kinetic trap for intermediates in L alpha/HII transitions (although it is possible that they are marginally more stable in a thermodynamic sense than the L alpha phase in a small temperature range below TH). It is also shown that arrays of ILAs should form metastable arrays with the same morphology and isotropic 31P-NMR resonances that are observed in isotropic and inverted cubic states. In particular, under some circumstances ILAs will assemble into a structure identical to the bicontinuous inverted cubic phase previously described in monoglycerides and very similar in morphology to structures observed in phospholipid systems. Finally, since isotropic and cubic states form from ILAs, which also can mediate fusion of unilamellar vesicles, unilamellar vesicles should fuse to at least some extent under the same conditions in which multilamellar samples of the same lipid form isotropic or inverted cubic states. This correlation has been observed.

Glycolipids↗

PubMed1987

Leishmania braziliensis: protein, carbohydrate, and antigen differences between log phase and stationary phase promastigotes in vitro.

When Leishmania species are grown in vitro, parasites from the stationary phase differ from those in log phase growth in being more infective and more resistant to complement and macrophage mediated killing. In the present study, log phase and stationary phase promastigotes of Leishmania braziliensis panamensis were compared at the molecular level. Differences in polypeptide and glycoprotein composition and antigenicity between log and stationary phase promastigotes of L. b. panamensis were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting; the former showed that two polypeptides were unique to log phase promastigotes and one was unique to stationary phase promastigotes. There were also differences in surface lectin binding characteristics of log and stationary phase promastigotes. Live stationary phase promastigotes bound more concanavalin and lentil lectin than log phase promastigotes, indicating a greater number of mannose residues on their surfaces.

Animals↗

PubMed1995

Retention and selectivity of flavanones on homopolypeptide-bonded stationary phases in both normal- and reversed-phase liquid chromatography.

Three linear polymers of repeating amino acid units, or homopolypeptides, have been individually covalently bonded to microparticulate silica and evaluated for liquid chromatographic separations. The retention and selectivity of seven flavanones were investigated on these stationary phases and a structurally similar, commercially available reference stationary phase, Chiraspher. All three of the homopolypeptide stationary phases retain solutes in the normal-phase mode. The aromatic-containing homopolypeptide stationary phases also retain solutes in the reversed-phase mode. Selectivity values for the flavanones were higher in the normal-phase mode; chiral selectivity was observed for the amphiphilic homopolypeptide stationary phase in the reversed-phase mode. The retention mechanism of each stationary phase is suggested based on the chemical nature and conformation of the corresponding homopolypeptide ligand.

Chromatography, Liquid↗

PubMed1984

C1q solid-phase radioimmunoassay: binding properties of solid-phase C1q and evidence that C1q-binding IgG complexes in systemic lupus erythematosus are not bound to endogenous C1q.

The binding properties of C1q solid-phase radioimmunoassay (C1q SPRIA) were examined, using heat-aggregated IgG (HAG) as the model of immune complexes (IC). The free, liquid-phase C1q, which was added to the C1q-coated tubes prior to the addition of HAG, had little inhibitory effect on binding of HAG to the solid-phase C1q, suggesting that the solid-phase C1q has a higher affinity for HAG than the liquid-phase C1q. On the other hand, more than 60% inhibition was seen when HAG was preincubated with the liquid-phase C1q. These binding properties of HAG to the solid-phase C1q in the presence of the liquid-phase C1q were not essentially altered by the heat inactivation or the addition of EDTA, suggesting that these pretreatments are not essential in C1q SPRIA. Next, in similar kinds of experiments, the binding properties of C1q-binding IgG complexes in SLE sera were investigated. In contrast to HAG, the binding capacity of IgG complexes in SLE sera to the solid-phase C1q was not inhibited by the preincubation with excess liquid-phase C1q. These findings suggest that C1q-binding IgG complexes in SLE sera detected by C1q SPRIA may not be bound to endogenous C1q in the circulation.

Antigen-Antibody Complex↗

PubMed1994

cAMP contributes to mossy fiber LTP by initiating both a covalently mediated early phase and macromolecular synthesis-dependent late phase.

Memory storage has a short-term phase that depends on preexisting proteins and a long-term phase that requires new protein and RNA synthesis. Hippocampal long-term potentiation (LTP) is thought to contribute to memory storage. Consistent with this idea, a cellular representation of these phases has been demonstrated in NMDA receptor-dependent LTP. By contrast, little is known about the NMDA receptor-independent LTP of the mossy fiber pathway. We find that mossy fiber LTP also has phases. Only late phase is blocked by protein and RNA synthesis inhibitors, but both phases are blocked by inhibitors of cAMP-dependent protein kinase, and both are stimulated by forskolin and Sp-cAMPS. During early phase, paired-pulse facilitation is occluded. This occlusion decays with the onset of late phase, consistent with its using a different mechanism. Thus, although Schaffer collateral and mossy fiber pathways use very different mechanisms for early phase, both use a cAMP-mediated mechanism for late phase.

Animals↗

PubMed1986

Role of head group structure in the phase behavior of amino phospholipids. 1. Hydrated and dehydrated lamellar phases of saturated phosphatidylethanolamine analogues.

Analogues of dimyristoylphosphatidylethanolamine (DMPE) have been prepared with head groups modified by N-alkylation, alkylation of carbon 2 of the ethanolamine group, or interposition of extra methylene segments between the phosphoryl and amino groups. The phases formed by these lipids in aqueous dispersions have been examined by high-sensitivity differential scanning calorimetry and Raman spectroscopy. All of the DMPE analogues examined, excepting N-methyl-DMPE but including N-ethyl-DMPE, form hydrated gel phases that are metastable with respect to a dehydrated "high-melting" solid phase that has been observed previously for DMPE itself. The properties and the conditions of formation of this high-melting phase are qualitatively distinct from those of the "subgel" phase, which is observed for dipalmitoylphosphatidylcholine and for some of the DMPE analogues examined in this study. The high-melting phases of different DMPE analogues all exhibit similarly tight packing of the acyl chains, which however do not pack according to a single type of subcell that can be universally and specifically associated with this phase. Increasing the size of the PE head group invariably decreases the melting temperature of the hydrated gel phase, even when the normal hydrogen-bonding capability of the head group is preserved. By contrast, addition of larger alkyl substituents to either the amino group or carbon 2 of the ethanolamine moiety substantially increases the transition temperature of the high-melting solid phase, indicating that the contributions of the head group to the energies of the hydrated gel and the high-melting phases are fundamentally different. Our results suggest that the head group structural requirements for a neutral phospholipid to form stable hydrated bilayers are rather stringent, a fact that may explain the overwhelming predominance of only a few such head group structures in most natural membranes.

Calorimetry, Differential Scanning↗

PubMed1981

Quantitative solid-phase Edman degradation for evaluation of extended solid-phase peptide synthesis.

Quantitative solid-phase Edman degradation was used for the amino acid sequence analysis of synthetic peptidyl-resins prepared by the Merrifield solid-phase procedure. A model peptide, Ala-[3H]Pro-Ala-Gly-Phe-Ala-Gly-, was synthesized on a solid support and was sequenced to measure the efficiency of the solid-phase sequencing protocol used. An average of 92% of the first four residues was removed from the peptidyl-resin as indicated by subtractive amino acid analysis. Quantitation of the radioactive proline residue at cycle 2 revealed that it was efficiently recovered both from the acid conversion procedure (99%) and also following high-pressure liquid chromatography of the phenylthiohydantoin (Pth) amino acid (88%). In order to facilitate identification and quantification of the side chain protected Pth amino acids, we prepared these derivatives and characterized them by high-pressure liquid chromatography. Thereafter, by the use of solid-phase Edman degradation as an analytical procedure, the synthesis of residues 2-118 of the heavy-chain variable region (VH) of a homogeneous rabbit antibody was undertaken. At 10-15-residue intervals during the solid-phase synthesis, samples of peptidyl-resin were removed from the synthesis vessel and sequenced. When gross synthetic errors caused by deletion of amino acids residues were detected, the solid-phase synthesis was terminated and restarted by using modified protocols. A 117-residue peptidyl-resin was prepared finally which possessed the desired amino acid sequence as indicated by a series of solid-phase Edman degradation experiments. In the final degradation experiment on the 117-residue peptidyl-resin, a 92% efficiency for the automatic Edman reaction was measured ([3H]Leu, penultimate amino-terminal residue). We have found two advantages for the concurrent use of solid-phase Edman degradation during an extended solid-phase synthesis: (1) on the basis of the level of error due to incomplete incorporation of amino acids, the solid-phase assembly could be terminated in favor of restarting the synthesis, hence avoiding further work on a defective product and (2) direct verification of incorporation of amino acids, which during acid hydrolysis are destroyed (Cys, Trp) or are deamidated (Asn, Gln), is possible by high-pressure liquid chromatography of the corresponding Pth derivatives.

Amino Acid Sequence↗

PubMed1990

[Phase 3 and phase 4 block in the accessory pathway].

Pacemaker activity at a site proximal to the area of a conduction disturbance has been postulated as depressing conduction in late diastole (phase 4 block). To elucidate the correlation between the site of phase 4 depolarization and that of a conduction disturbance, we examined seven patients with intermittent Wolff-Parkinson-White syndrome who had tachycardia (phase 3) and bradycardia (phase 4) dependent on block in the accessory pathway. In each patient, antegrade conduction over the accessory pathway was absent at the sinus rate. During premature atrial stimulation a "window" of accessory pathway conduction was identified in each patient. The outer limit of the window ranged from 420 to 670 ms; the inner limit, from 330 to 620 ms. The duration of the window ranged from 20 to 160 ms. Four patients with orthodromic atrioventricular reentrant tachycardia exhibited preserved retrograde accessory pathway conduction. In one patient with unsustained orthodromic atrioventricular reentrant tachycardia, retrograde accessory pathway conduction also exhibited phase 3 and phase 4 blocks. The remaining two patients had no retrograde accessory pathway conduction. In two patients, retrograde concealed conduction in the accessory pathway induced by ventricular stimulation eliminated a phase 4 block in antegrade accessory pathway conduction. These results suggest that 1) an antegrade phase 4 block may have phase 4 depolarization in the accessory pathway and block at the ventricular insertion of the accessory pathway; 2) a retrograde phase 4 block may have a conduction disturbance at the atrial insertion of the accessory pathway; and 3) a complete retrograde block may occur at the atrial insertion of the accessory pathway.

Adolescent↗

PubMed1981

Analysis of the hexagonal II phase and its relations to lipidic particles and the lamellar phase. A freeze-fracture study.

Model systems of phosphatidylethanolamine (PE) and cardiolipin (DPG), as pure components and in binary mixtures with phosphatidylcholine (PC) have been morphologically analysed. The relation between the hexagonalII (HII) phase and lipidic particles as well as between the HII phase and the lamellar phase has been studied. Moreover, the periodicity of the various HII tubes was determined. (1) The periodicity of the HII phase of cardiolipin is dependent on the cation involved. DPG-Ca exhibits the smallest tube to tube distance when compared to Mg2+ and Mn2+. Moreover, the DPG-Ca tubes are quite straight, in contrast to the Mg2+ and Mn2+ tubes, which appear to be frequently curved. (2) HII tubes with two distinct diameters have been observed in HII phase containing lipid mixtures. The thickness of the HII tube is related to the composition of the tube. In the cardiolipin-lecithin system, structural separation of the pure cardiolipin HII phase has been suggested with Mg2+ and Mn2+, but not with Ca2+. (3) Models for the HII to lamellar phase transition and for the HII phase to the lipidic particles are presented. (4) Lipidic particles are exclusively found in lipid model systems, which contain HII phase favouring lipids. Morphological evidence is presented which suggests these lipidic particles represent inverted micells. These observations include: (i) there is a strong topological and quantitative relation between HII tubes and lipidic particles, (ii) lipidic particles occur densely packed in conglomerates without the presence of a smooth layer.

Animals↗