Vesicle surface charge and polylysine modification of ultraviolet absorption by the olefinic bonds in charged lipid

The results of electrical conductivity and ultraviolet absorption studies on bilayer vesicles, composed of various mixtures of saturated dipalmitoylphosphatidylcholine (DPPC)and unsaturated bovine brain phoaphatidylserine (PS), in the presence and absence of polylysine indicate the following. (i) The two kinds of lipid maintain a strong transbilayer segregation over a wide range of proportions. The charged lipid (PS) preferentially locates in the inner, at PS proportions of 33% or less, and in the outer layer of the membranes when its proportion is increased to 50%. (ii) At PS proportions of 33% of less, where DPPC is the major component of the outer layer, the ability of polylysine to modify ultraviolet absorption by the olefinic bonds in the PS depends on the fluidity of the phosphatidylcholine. At higher PS proportions, where PS preferentially locates in the outer layer, modification of the ultraviolet absorption spectrum of the lipid by polylysine occurs only when the surface charge of the vesicles is diminished by the addition of bivalent metal ions. (iii) The polylysine-induced change in the ultraviolet absorption spectrum of the olefinic bonds in the vesicles was found to be very similar to that induced by dispersing unsaturated fatty acids in water rather than dissolving them in a nonpolar solvent. This suggests that polylysine modification of the vesicles spectrum may be the result of deep hydrophobic penetration by the polypeptide causing hydration and(or) parallel alignment of the dipole moments of the absorbing chromophores.     

The effect of temperature on lipid-n-alkane interactions in lipid bilayers

The relationship between age-related alterations in the lipid composition of cultured rat-heart fibroblasts and several biochemical and biophysical parameters was investigated. Aged (14-15-day-old) cultures displayed higher mole ratios of sphingomyelin to phosphatidylcholine, as well as elevated cholesterol levels. A concomitant increase was observed in the total protein content of the cells and in the Vmax values of both membranal and cytoplasmic marker enzymes. Fluorescence photobleaching recovery was employed to study the lateral mobility of the lipid probe NBD-phosphatidylethanolamine and of membrane glycoproteins that bind succinylated concanavalin A. The mobile fractions of both probes were higher in aged cultures, while the lateral diffusion coefficients were lower. To further demonstrate the dependence of the above parameters on the cellular lipid composition, we have manipulated the lipid composition of old cultures by treatments with liposomes (small unilamellar vesicles) of specific compositions. Treatments which reversed the lipid composition towards that of young (5-6-day-old) cultures caused a concomitant reversal of the measured biochemical and biophysical parameters to the values observed in young cultures. These findings suggest that alterations in the organization and mobility of cell membrane constituents are involved in mediating changes in cellular functions. In view of our previous findings on cultures of rat-heart myocytes (Yechiel, E., Barenholz, Y. and Henis, Y.I. (1985) J. Biol. Chem. 260, 9132-9136), it appears that the modulation of cellular properties through the membrane lipid composition may be a general phenomenon in many cell types.     

Electrostatic interactions at charged lipid membranes. Hydrogen bonds in lipid membrane surfaces

Hydrogen-bonded structures within lipid membrane surfaces are not disrupted by water and are of thermodynamic and therefore potential structural importance in biological systems.     

Multiple bonds for the lipid interest

Polyene lipids and alkyne lipids allow study of lipid organization, dynamics and metabolism. Both types of lipids contain multiple bonds as the essential functional group, leading to minimal disturbance of the hydrophobic properties on which the characteristic behavior of lipids is based. Polyene lipids can directly be traced due to their intrinsic fluorescence, while alkyne lipids need the copper-catalyzed click reaction to an azido-reporter for detection. This review describes recent developments in synthesis and application of both types of lipid analogs with emphasis on metabolic tracing and microscopy imaging. This article is part of a Special Issue entitled Tools to study lipid functions.     

Geometrical effects of phospholipid olefinic bonds on the structure and dynamics of membranes: A molecular dynamics study

The trans isomers of fatty acids are found in human adipose tissue. These isomers have been linked with deleterious health effects (e.g., coronary artery disease). In this study, we performed molecular dynamics simulations to investigate the structures and dynamic properties of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) and 1-palmitoyl-2-elaidoyl sn-glycero-3-phosphatidylcholine (PEPC) lipid bilayers. The geometry of the olefinic bond and membrane packing effects significantly influenced the conformations and dynamics of the two CC single bonds adjacent to the olefinic bond. For the PEPC lipid, the two CC single bonds adjacent to the olefinic bond adopted mainly nonplanar skew–trans and planar cis–trans motifs; although the cis conformation featured relatively strong steric repulsion, it was stabilized through membrane packing because its planar structure is more suitable for membrane packing. Moreover, membrane packing effects stabilized the planar transition state for conformational conversion to a greater extent than they did with the nonplanar transition state, thereby affecting the dynamics of conformational conversion. The rotational motions of the first neighboring CC single bonds were much faster than those of typical saturated CC single bonds; in contrast, the rotational motions of the second neighboring CC single bonds were significantly slower than those of typical saturated torsion angles. The packing of PEPC lipids is superior to that of POPC lipids, leading to a smaller area per lipid, a higher order parameter and a smaller diffusion coefficient. The distinct properties of POPC and PEPC lipids result in PEPC lipids forming microdomains within a POPC matrix.     

The effect of ultraviolet irradiation on soluble collagen

1. The effect of ultraviolet irradiation on acid-soluble and neutral-salt-soluble calf-skin collagen was studied by chromatography, gel filtration, amino acid analysis and sedimentation of the sub-units, and the reaction kinetics of degradation were obtained from viscosity and optical rotation measurements. 2. It was demonstrated that, whereas the structure of neutral-salt-soluble calf-skin collagen may be represented by the formula (alpha(1))(2)alpha(2), the acid-soluble extract has the formula alpha(1).(alpha(2))(2). The acid-soluble collagen is also unusual in containing a large amount of a component that could be beta(22). 3. Ultraviolet irradiation causes the progressive degradation of the collagen molecule into smaller molecular fragments that subsequently lose their helical nature. The rate constants show that the denaturation of soluble collagens by ultraviolet irradiation is much slower, under the conditions used, than denaturation by heat or enzymes.     

The effect of ultraviolet irradiation on acid-soluble collagen

1. A study has been made of the effect of ultraviolet irradiation on the conformational changes taking place in cooled solutions of thermally denatured acid-soluble calf-skin collagen. 2. The increase in negative rotation and viscosity at 15° for irradiated and thermally denatured collagen solutions becomes less as the irradiation dose is increased. 3. The principal effect of ultraviolet irradiation is the fission of the primary collagen chains, eventually yielding chain lengths incapable of stabilizing a helical structure. 4. The effects of ultraviolet irradiation on acid-soluble collagen may be closely correlated with similar effects on neutral salt-soluble collagen.     

The effect of ultraviolet irradiation on collagen-fold formation

1. A study has been made of the effect of ultraviolet irradiation, in the presence of air and nitrogen, on the conformational changes taking place in cooled solutions of gelatin prepared from thermally denatured neutral-salt-soluble collagen. 2. The increase in negative rotation and viscosity at 15 degrees for irradiated and thermally denatured solutions of collagen becomes less as the irradiation time is increased. 3. The principal effect of ultraviolet irradiation is the fission of the primary collagen peptide chains, eventually yielding chain lengths incapable of stabilizing a helical structure. 4. Irradiation in both air and nitrogen results in a loss of tyrosine, histidine and phenylalanine, with more denaturation occurring in the presence of nitrogen.