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- Mesoscopic Structure in the Chain-Melting Regime of Anionic ...Mesoscopic Structure in the Chain-Melting Regime of Anionic Phospholipid Vesicles: DMPG
Biophysical Journal, Volume 86, Issue 6, 1 June 2004, Pages 3722-3733
K.A. Riske, L.Q. Amaral, H.-G. Döbereiner and M.T. Lamy
AbstractIn a range of low ionic strength, aqueous dispersions of the anionic phospholipid DMPG (dimyristoylphosphatidylglycerol) have a transparent intermediate phase (IP, between and ) between the turbid gel and fluid membrane phases, evidenced in turbidity data. Small angle x-ray scattering results on DMPG dispersions show that, besides the bilayer peak present in all phases, a peak corresponding to a mesoscopic structure at ∼400Å is detected only in IP. The dependence of this peak position on DMPG concentration suggests a correlation in the bilayer plane, consistent with the stability of vesicles in IP. Moreover, observation of giant DMPG vesicles with phase contrast light microscopy show that vesicles “disappear” upon cooling below and “reappear” after reheating. This further proves that although vesicles cannot be visualized in IP, their overall structure is maintained. We propose that the IP in the melting regime corresponds to unilamellar vesicles with perforations, a model which is consistent with all described experimental observations. Furthermore, the opening of pores across the membrane tuned by ionic strength, temperature, and lipid composition is likely to have biological relevance and could be used in applications for controlled release from nanocompartments.
Abstract | Full Text | PDF (464 kb) - Determination of Melting Sequences in DNA and DNA-Protein Co...Determination of Melting Sequences in DNA and DNA-Protein Complexes by Difference Spectra
Biophysical Journal, Volume 9, Issue 4, 1 April 1969, Pages 473-488
Anthony P. Russell, Robert L. Herrmann and LeNeal E. Dowling
AbstractA graphical formula is presented for determining the base ratio of melted DNA. By use of this formula, the composition of sequences which melt in different portions of the melting curves of DNA, DNA, and mouse DNA were determined. As the DNA melts, the per cent of adenine and thymine (AT) in the melted sequences decreases linearly with temperature. The average composition of sequences which melt in a given part of the melting curve is proportional to the base ratio of the DNA. The concentration and average composition of sequences were determined for three parts of the melting curves of the DNA samples, and a frequency distribution curve was constructed. The curve is symmetrical and has a maximum at about 56% AT. The distribution of GC-rich sequences on the chromosome was estimated by shearing, partially melting, and fractionating the DNA on hydroxylapatite. GC-rich sequences appear to occur every thousand base pairs, and have a maximum length of about 180 base pairs. The graphical formula was applied to the determination of the composition of sequences which melt in different parts of the melting curve of chromatin. Throughout the melting curve, the composition of the melting sequences is about 60% AT, which appears to suggest that relatively long sequences are melting simultaneously. Their melting temperature may be a function of the composition of the protein on different parts of the DNA. The problem of light scattering in DNA-protein and DNA was also investigated. A formula is presented which corrects for light scattering by relating the intensity of the scattered light to the rate of change of absorbance of DNA with wavelength.
Abstract | PDF (973 kb) - Energetics of Hydrophobic Matching in Lipid-Protein Interact...Energetics of Hydrophobic Matching in Lipid-Protein Interactions
Biophysical Journal, Volume 94, Issue 10, 15 May 2008, Pages 3996-4013
Derek Marsh
AbstractLipid chain length modulates the activity of transmembrane proteins by mismatch between the hydrophobic span of the protein and that of the lipid membrane. Relative binding affinities of lipids with different chain lengths are used to estimate the excess free energy of lipid-protein interaction that arises from hydrophobic mismatch. For a wide range of integral proteins and peptides, the energy cost is much less than the elastic penalty of fully stretching or compressing the lipid chains to achieve complete hydrophobic matching. The chain length dependences of the free energies of lipid association are described by a model that combines elastic chain extension with a free energy term that depends linearly on the extent of residual mismatch. The excess free energy densities involved lie in the region of 0.5–2.0.nm. Values of this size could arise from exposure of hydrophobic groups to polar portions of the lipid or protein, but not directly to water, or alternatively from changes in tilt of the transmembrane helices that are energetically comparable to those activating mechanosensitive channels. The influence of hydrophobic mismatch on dimerization of transmembrane helices and their transfer between lipid vesicles, and on shifts in chain-melting transitions of lipid bilayers by incorporated proteins, is analyzed by using the same thermodynamic model. Segmental order parameters confirm that elastic lipid chain distortions are insufficient to compensate fully for the mismatch, but the dependence on chain length with tryptophan-anchored peptides requires that the free energy density of hydrophobic mismatch should increase with increasing extent of mismatch.
Abstract | Full Text | PDF (386 kb) - …more
Copyright © 1974 The Biophysical Society. All rights reserved.
Biophysical Journal, Volume 14, Issue 3, 178-188, 1 March 1974
doi:10.1016/S0006-3495(74)85905-9
Articles
Spin Label Translational Diffusion in Solid Tristearin
G.E. Cohn, A.D. Keith and Wallace Snipes
Abstract
Translational diffusion of the intermediate chain length spin label 7N14 has been detected and studied in a lipid environment which is in the bulk solid state. Under favorable circumstances this can occur at temperatures as much as 50°C below the optical melting point. Translational diffusion allows 7N14 molecules to coalesce into impurity pools of high spin label concentration. Two other spin labels, 2N3 and 14N27, do not show a tendency to form such impurity pools. While 2N3 undergoes rapid tumbling at temperatures far below the melting point of the tristearin matrix, the molecules remain in an isolated state with no evidence of spin exchange. 14N27 is restricted in rotational motion in the solid matrix and also does not form impurity pools.
