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Biomedical subjects

L Finegold

Publications and source records attributed to L Finegold.

At least 19 recordsLinked to original sources
PubMed2001

Miscibility gap in fluid dimyristoylphosphatidylcholine:cholesterol as "seen" by x rays.

A binary mixture of dimyristoylphosphatidylcholine (DMPC) and cholesterol displays a fluid miscibility gap under excess water conditions. Effects due to the imperfect miscibility of the two amphiphiles are studied near to and far from thermodynamic equilibrium by time-resolved small angle x-ray diffraction. The experiment discloses that this mixture phase separates when leaving the miscibility gap upon heating, a transition that is not included in current phase diagrams. This transition appears to be reversible and shows a temperature hysteresis of only a few degrees. We suggest a model in which the transition is driven with increasing temperature by a movement of the cholesterol away from the hydrophilic-hydrophobic interface toward the hydrophobic core of the bilayer.

Biophysical Phenomena↗
PubMed1994

A new liquid crystalline phase in phosphatidylcholine bilayers as studied by X-ray diffraction.

Model membranes of diacylphosphatidylcholines (CnPC), with saturated linear acyl chains of n > 12 carbons, show a single sharp phase transition (known as the main transition) between the gel phase P beta' and the liquid crystalline phase L alpha with differential scanning calorimetry. However, C12PC (dilauroylphosphatidylcholine) shows, as well as the sharp transition at -2 degrees C, a broad peak at 5 degrees C, originally observed by S. Mabrey and J.M. Sturtevant. The broad peak is not artificial: between the two peaks a new phase Lx was predicted for (C12PC) bilayers on the basis of calorimetry (Finegold, Shaw and Singer, Chem. Phys. Lipids 53 (1990), 177-184). The existence of Lx has now been confirmed by synchrotron X-ray diffraction on samples identical to those of the previous work, of similar preparation and at corresponding scan rates. With temperature, both small-angle (long lamellar) and wide-angle (hydrocarbon chain) spacings show abrupt discontinuities, and separate broader changes, at temperatures corresponding to the calorimetric sharp and broad peaks, respectively. All the X-ray diffraction profiles and spacing results are consistent with the following phase scheme with increasing temperature: gel ripple phase P beta'-->new, less ordered liquid crystalline phase Lx-->most disordered liquid crystalline phase L alpha. The phase Lx possibly exists in other CnPCs, and its examination may provide details of the main transition. Because Lx exists at a higher temperature than the main transition from P beta', it promises to be of biological relevance.

Calorimetry, Differential Scanning↗
PubMed1990

The formation of multilamellar vesicles from saturated phosphatidylcholines and phosphatidylethanolamines: morphology and quasi-elastic light scattering measurements.

The aggregation properties of diacyl phosphatidylcholines (PC) and phosphatidylethanolamines (PE), with linear symmetrical saturated chains, were characterized at temperatures below and above the lipid solid to fluid transition. PEs in the solid state form bundles of closely apposed flat bilayer stacks which at the solid to fluid transition temperature fold into closed multilamellar vesicles. On the other hand, PCs in the solid state form extended multilayer sheets. At the solid to fluid transition, multilamellar vesicles appear to "bud off" from the surface. Quasi-elastic light scattering (QELS) measurements indicated that for the PEs, bundle size is independent of acyl chain length n, but that the sizes of vesicles which form at the solid to fluid transition are positively correlated with n. The results of temperature jump experiments showed that once the transition temperature was reached, vesicle formation was largely complete within 30 s.

Calorimetry, Differential Scanning↗
PubMed1990

Interaction of cholesterol with saturated phospholipids: role of the C(17) side chain.

Cholesterol and 5-androsten-3 beta-ol differ structurally only in the presence of an eight carbon side chain at the C(17) position in the former sterol. Both molecules decrease the main transition enthalpy change (delta H) in a series of phosphatidylcholines and phosphatidylethanolamines, of acyl chain length n, with the reduction being a linear function of sterol concentration (c). The sterol concentrations at which delta H = 0 bear a straight line relationship to n and are equivalent for both cholesterol and 5-androsten-3 beta-ol. In addition, both sterols give identical delta H versus c slopes. These results underscore the importance of acyl chain length in the cholesterol/phospholipid interaction and also indicate that the cholesterol C(17) side group is not an essential requirement for the capacity of the sterol to decrease the enthalpy change of the main transition.

Acylation↗
PubMed1990

Cholesterol interacts with all of the lipid in bilayer membranes. Implications for models.

The interaction of cholesterol with lipid membranes has been studied by differential scanning calorimetry on liposomes, a technique which involves only the natural lipids, with no exogeneous probes. The influence of cholesterol at different molar percent concentrations c on the enthalpy delta H of the main gel to liquid crystal phase transition of saturated phosphatidylcholines of acyl chain length n = 12-20 was well represented by delta H = -9.43 + 1.01n - 0.268c kcal/mol. The linear dependence of delta H simultaneously upon chain length n and upon cholesterol concentration c shows clearly that cholesterol interacts with the deeper part of the lipids, as well as the superficial parts. This observation is not accommodated in any of the current models of cholesterol-lipid interactions.

Calorimetry, Differential Scanning↗
PubMed1990

Composition and thermal properties of membrane lipids in cryptoendolithic lichen microbiota from antarctica.

In Antarctica there exists a cryptoendolithic microbiota which survives extremely low temperatures. Fatty acid analysis of the membrane phospholipids of this microbial community showed a predominance of polyunsaturated fatty acids. Artificial membranes made from the purified community phospholipids remained fluid to below -20 degrees C and had unusual hydration properties.

Journal Article↗
PubMed1986

The metastability of saturated phosphatidylcholines depends on the acyl chain length.

We report the peak temperatures and enthalpies of the main (gel to liquid crystal) transitions and 's-transitions' of symmetric saturated PC's (CnPC) with n varying from 12 to 22, where s-transition is defined as the transition between metastable and stable phases. The line for s-transition peak temperature versus n (t = 1.98n -16.0 degrees C) crosses the corresponding pre- and main-transition curves between n = 12 and 14. We also find that the metastability pattern for lipids of n less than 14 is different to that for n greater than 14 (and is similar to that of the phosphatidylethanolamine analogs). For n greater than 14 the enthalpy of the s-transition decreases with increasing n and extrapolates to zero above n = 20, implying that the s-(orthorhombic) and gel (quasi-hexagonal) phases become identical. That simultaneous gel-liquid crystal transition and metastability is restricted to the range n = 12 to 20 may be correlated with the predominance in natural lipids of these acyl chain lengths.

Liposomes↗
PubMed1986

Molecular aspects of adaptation to extreme cold environments.

Here are reviewed and summarized the strategies adopted by living organisms to survive low temperatures, from a molecular and membrane point of view. The presentation is aimed at a wide variety of readers. Two prime examples of connections between biological cold adaptation and the molecular level are (1) antifreeze proteins in fish from cold sea water, (the DNA sequence of the protein gene is now known) (2) the fluidity characteristics of cell membranes in a wide variety of organisms. In model membranes of phospholipids, stabler "s-phases" have recently been found to form at low temperatures. Antarctic endolithic organisms, living just under the surface of rocks, are exposed to long periods of low temperatures, and may develop such phases in their membranes. In the saturated phosphatidyl cholines, only lipids with a restricted range of acyl chain lengths show simultaneously s-phases and a main transition : This restricted range is about the restricted range found in natural membranes. The s-phases also form in the presence of natural cryoprotectants, and may be connected with botanical vernalization.

Acclimatization↗
PubMed1986

Effect of saturated phosphatidylcholines on the functional properties of reconstituted cytochrome oxidase.

Cytochrome oxidase was incorporated into liposomes, at various protein/lipid ratios, composed of either a phosphatidylcholine of varying chain length and symmetry or asolectin. Catalytic activity and respiratory control were assayed at two temperatures. All preparations showed higher activity at low protein/lipid ratios, but only asolectin showed respiratory control. A spectroscopic determination of the vectorial orientation of oxidase molecules showed that, for proteoliposomes with saturated lipids, 100% of oxidase molecules could be reduced by external substrate as compared with 75% for asolectin proteoliposomes. Freeze-fracture electron microscopy confirmed that oxidase was incorporated into these proteoliposomes and differential scanning calorimetry indicated that the protein induces significant disruption in the long range packing of the saturated phospholipids. We propose that the oxidase molecules in proteoliposomes formed from saturated phosphatidylcholines do not display respiratory control because they are unable to assume the transmembrane orientation necessary for full vectorial activity.

Animals↗
PubMed1985

Permeability and morphology of low temperature phases in bilayers of single and of mixtures of phosphatidylcholines.

The properties of subtransitions were studied in aqueous dispersions of saturated phosphatidylcholines (PC) by means of permeability measurements, freeze-fracture electron microscopy, and differential scanning calorimetry (DSC). For dispersions of C16PC, a C16PC analog (2,3-dipalmitoyl-cyclopentano-1-phosphocholine with four methylene residues between the nitrogen and the phosphorus atoms) and C17PC, there was good agreement between phase properties (including subtransitions) as observed by DSC and temperature-related permeability. C16PC and C17PC dispersions also displayed a 'crinkled' surface morphology in the subgel state. The phase diagram for mixtures of C14PC and C16PC was consistent with ideal mixing of these two components in the subgel state and also illustrated the relative independence of the subtransition on acyl chain length as compared to the pre- and main transitions. Together, these results indicate that (i) permeability, DSC and freeze-fracture electron microscopy measurements do correlate reasonably well with the existence of a subgel state, (ii) mixtures of lipids with similar acyl chain lengths can be used to investigate subtransitions, (iii) the development of a subtransition appears to be mainly a function of the non-acyl chain moiety of the phospholipid.

Calorimetry, Differential Scanning↗
PubMed1984

Phosphatidylcholine bilayers: subtransitions in pure and in mixed lipids.

Aqueous dispersions of C14, C16, C17 and C18 phosphatidylcholines (PC, where Cn denotes di-acyl of n carbons per chain), and mixtures of C14/C16PC and C16/C17PC were prepared and their thermal properties studied by differential scanning calorimetry (d.s.c.) after sample storage at 2-6 degrees C for up to 22 days. C16PC and C18PC display subtransitions at 22 degrees C and 29 degrees C, respectively, as previously reported by Chen et al. (Proc. Natl. Acad. Sci. U.S.A. 77 (1980) 5060-5063). C17PC shows two subtransitions at 21 degrees C and 26 degrees C, respectively, which are independent of each other. Although C16PC and C17PC individually develop subtransitions, an equimolar mixture does not. However, mixtures of C14/C16PC containing 10 or more mol% of C14PC do display a subtransition. These results underscore the primary dependence of subtransition formation in phosphatidylcholine dispersions on acyl chain structure.

Lipid Bilayers↗
PubMed1976

Cell membrane fluidity: molecular modeling of particle aggregations seen in electron microscopy.

The first simulation of the fluid mosaic model is reported. Intra-membrane particles, initially "placed" randomly in a membrane with fluid properties, are allowed to diffuse in the plane of the membrane and to interact with one another, in a model using molecular parameters. The resulting particle aggregates are very similar to those observed in freeze-fracture electron microscopy.

Diffusion↗