Recombinant lipoproteins: implications for structure and assembly of native lipoproteins.
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Animals↗
Biomedical subjects
D M Small
Publications and source records attributed to D M Small.
The ionization behavior of bile acids in different aqueous environments.
The ionization behavior of cholic acid, deoxycholic acid, and chenodeoxycholic acid in a variety of physiologically important molecular environments was studied using 13C NMR spectroscopy. The apparent pKa of the carboxyl group was determined from titration curves obtained from the dependence of the carboxyl carbon chemical shift on pH. Using 90% 13C isotopic substitution of the carboxyl carbon, a complete titration curve was obtained for cholate at a concentration below its critical micelle concentration and solubility limit in water. Incorporation of 12 mole % bile acid into mixed micelles with its taurine conjugate prevented precipitation of the unconjugated bile acid, and titration curves for cholic, deoxycholic, and chenodeoxycholic acids in the mixed micelles were obtained. The apparent pKa was also determined for 13C-enriched bile acids complexed with bovine serum albumin and in egg phosphatidylcholine vesicles. For monomers, micelles, and BSA complexes of all three bile acids and for deoxycholic and chenodeoxycholic acid in vesicles, one magnetic environment was observed. In contrast, two environments, both titratable, were detected for cholic acid in phosphatidylcholine vesicles. The apparent pKa's of the bile acids in the different environments ranged from 4.2 to 7.3. At pH 7.4, as monomers or bound to albumin, the bile acids were fully ionized, but when associated with phosphatidylcholine vesicles they were only partially ionized. In addition, aspects of the molecular motion and relative hydrophobicity of the bile acid carboxyl group in the environments studied were discerned from chemical shift, line-width, and lineshape data.
Bile Acids and Salts↗
Molecular motions and thermotropic phase behavior of cholesteryl esters with triolein.
The phase behavior of cholesteryl esters with triglyceride has been characterized by differential scanning calorimetry (DSC), light microscopy, and polarizing light microscopy (PLM). Temperature-dependent molecular motions determined by 13C NMR spectroscopy were correlated with thermotropic phase behavior. Two systems, cholesteryl oleate (CO) and a 3/1 w/w mixture of cholesteryl linoleate (CL) and CO, were examined in the presence of small amounts of triolein (TO). Both systems exhibited metastable cholesteric and smectic (or only smectic) phases. Increasing amounts of TO progressively lowered the liquid-crystalline phase transition temperatures and eventually abolished the cholesteric phase, but at differing amounts of TO for the two systems (between 4% and 5% with CL/CO and between 7% and 10% with CO). DSC and PLM showed a progressive broadening of the phase transitions as well as an overlapping of the temperature ranges of the cholesteric and smectic phases. At greater than or equal to 4% TO, a separate isotropic liquid phase coexisted with liquid-crystalline phases. 13C NMR spectroscopy was used to monitor the molecular motions of the cholesteryl ester steroid ring and acyl chain in liquid and liquid-crystalline phases. In the liquid phase, no significant changes in fatty acyl motions, as reflected in spin-lattice relaxation time (T1) and nuclear Overhauser enhancement (NOE) values, were found on addition of TO. The line width (v 1/2) of the steroid ring resonances increased markedly near (1-5 degrees C above) the isotropic liquid----liquid-crystal phase transition temperature (TLC). However, the C3/C6 v 1/2 ratio at 1 degree C above TLC was greater for mixtures exhibiting an isotropic----cholesteric transition than for mixtures exhibiting an isotropic----smectic transition. Rotational correlation times calculated for motions about the long molecular axis and the nonunique axis showed (i) that the ring motions became more anisotropic as TLC was approached and (ii) that the motions were more anisotropic at TLC + 1 degree C for systems exhibiting a cholesteric phase than for systems exhibiting only a smectic phase. 13C line widths in spectra of the cholesteryl ester liquid-crystalline phases suggested that TO perturbed the cholesteryl ester intermolecular interactions and increased the rates of cholesteryl ester molecular motions relative to neat esters.
Calorimetry, Differential Scanning↗
Structure and polymorphism of 1,2-dioleoyl-3-acyl-sn-glycerols. Three- and six-layered structures.
Triacylglycerols, which usually contain at least one unsaturated fatty acid, are the most important forms of stored biological lipids in teleosts, mammals, and most plants. Since the physical properties of such mixed-chain triacylglycerols are poorly understood, a systematic study of such compounds has been initiated. Stereospecific 1,2-dioleoyl-3-acyl-sn-glycerols were synthesized with even carbon saturated fatty acyl chains of 14-24 carbons in length. Their polymorphic behavior was examined by differential scanning calorimetry and X-ray powder diffraction. The thermal behavior revealed from one to four major polymorphic transitions depending upon saturated chain length. Plots of enthalpy of fusion and entropy vs. carbon number for melting of the most stable polymorph were linear throughout the series with slopes of 1.0 kcal/mol per carbon atom and 2.6 cal/(mol K) per carbon atom, respectively. These slopes indicate that the saturated chains are packed in a well-ordered tightly packed lattice. When the compounds were rapidly cooled to 5 degrees C, X-ray powder diffraction revealed strong beta' (ca. 3.8 and 4.2 A) reflections and weak beta (ca. 4.6 A) reflections. The beta subcell reflections intensified when the compounds were heated to within 5 degrees C of the melting temperature of the highest melting polymorph. Evidence of an alpha phase was not seen on 30-min X-ray exposures for any of the compounds. In the proposed packing arrangement the saturated and unsaturated chains are segregated into layers. The stable form of all compounds exhibits a triple layer packing mode in which a bilayer of oleoyl chains is segregated from an interdigitated layer of saturated chains.(ABSTRACT TRUNCATED AT 250 WORDS)
Calorimetry↗
Synthesis and polymorphism of 3-acyl-sn-glycerols.
3-Acyl-sn-glycerols with even-numbered saturated fatty acyl chains from decanoate to lignocerate were synthesized. Successful hydrolysis of the long acyl chain intermediate 1,2-isopropylidene-3-acyl-sn-glycerols from stearate to lignocerate was accomplished by applying the compounds to silica gel and exposing them to hydrogen chloride gas at -75 degrees C. The purity of the compounds was checked by boric acid impregnated thin-layer chromatography, 13C NMR, and reverse-phase high-pressure liquid chromatography. Differential scanning calorimetry and X-ray diffraction techniques were used to study the polymorphism of the compounds. In the beta phase obtained from solvent of crystallization, the acyl chain packing was in a two-dimensional oblique lattice with specific chain-chain interactions with a tilt angle of 55.4 degrees from the bilayer plane. The thickness of the region containing two glycerol head groups was 12.7 A. The phase transition enthalpy of melting for the beta phase was 1.06 kcal/mol of CH2. On being cooled these compounds crystallized reversibly to an unstable alpha phase, which on being further cooled underwent a second crystallization to a beta or beta' phase. The thermodynamic parameters and long spacings of these compounds in both beta and alpha phases were linear, indicating isostructural packing in each phase. The enthalpy of the melting transition of the alpha phase was 0.69 kcal/mol of CH2. In this phase, the chains were packed in a hexagonal lattice with nonspecific chain-chain interactions. The thickness of the head-group region (12.2 A) and the tilt angle (55 degrees) of the acyl chains in the alpha phase were very similar to those in the beta phase.
Calorimetry↗
Some speculations on the deposition of cholesterol in aortic lesions of familial hypercholesterolemia.
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Aorta↗
Lateral chain packing in lipids and membranes.
The aliphatic chains of many biologically important lipids are heterogeneous and often related to the functions of the molecules. Certain phospholipids containing arachidonic acid may serve as precursors for prostaglandins, certain diglycerides may serve as second messengers for certain membrane-triggered reactions (43), and other phospholipids containing a very short chain in the two position may serve as vasoactive hormones (44). The packing of such molecules is of interest. The evidence is quite clear from both the conformation of saturated and unsaturated molecules and from mixing experiments in the solid state that long and short chains don't mix well, nor do unsaturated and saturated chains, even if they are of the same chain length. There is even some evidence to indicate that some degree of chain segregation occurs even in the liquid state. However, different chains are often associated through covalent bonds, e.g., in wax esters, diacylglycerols, triacylglycerols, and phospholipids. A variety of possibilities for chain segregation are present in the neat phases of wax esters, ceramides, diacylglycerols, and triacylglycerols. However, in the unique case of membrane lipids like phospholipids or sphingolipids, the two chains are forced to lie side by side by virtue of the interaction of the polar group with water, and thus interactions between different chains must occur. Most of the evidence suggests that, when a solid phase results in these systems, the nonspecific chain packing mode (hexagonal chain packing) is preferred. In fact, for all of the phospholipids studied thus far, clearcut evidence of specific chain-chain interaction in molecules having both unsaturated and saturated chains has never been observed. However, for mixed chain triacylglycerols, evidence of specific chain-chain interactions (beta' and even beta) has been found and some suggestions have been given as to how this might occur through chain segregation mechanisms in the neat state. The literature suggests that further work needs to be done on the interaction of different chains that are covalently linked to the same molecule. Such studies will lead to a better understanding of the structure of lipid bilayers, membranes, lipoproteins, and lipid deposits.
Chemical Phenomena↗
Reassembled plasma low density lipoproteins. Phospholipid-cholesterol ester-apoprotein B complexes.
Reassembled low density lipoprotein (LDL) complexes have been prepared by the interaction of lipid-free sodium deoxycholate-solubilized apoprotein B (apoB) of native human LDL with preformed, 200 A in diameter, microemulsions of cholesteryl oleate (CO), surface-stabilized by either egg yolk phosphatidylcholine ( EYPC ) or dimyristoyl phosphatidylcholine (DMPC). Gel chromatography of PC/CO/apoB complexes shows co-elution of the complex at 43% PC, 43% CO, and 14% apoB. Negative stain electron microscopy shows the particles to be circular, homogeneous, and approximately 200 A in diameter. PC/CO/apoB complexes exhibit beta-migration on agarose gels and show one high molecular weight protein band on 3.0% sodium dodecyl sulfate-polyacrylamide gels. Differential scanning calorimetry and x-ray scattering show the lipids in the complexes to undergo at least two specific thermal transitions depending on lipid composition, one associated with the core-located cholesterol esters similar to LDL and the protein-free microemulsions and the other from the phospholipid forming the surface monolayer. In addition, particle disruption-protein unfolding/denaturation occur irreversibly at 80-85 degrees C. At 4 degrees C, the secondary structure of apoB on complexes of EYPC /CO/apoB is similar to that of native LDL. For complexes of DMPC/CO/apoB, the secondary structure shows less alpha-helix which correlates with the difference in surface lipid environment. The reassembled complexes of PC/CO/apoB provide a defined system in which the components may be varied systematically in order to study the molecular organization, molecular interactions, and metabolism of LDL.
Apolipoproteins↗
Physical properties of cholesteryl esters.
Cholesteryl esters, the intracellular storage form and intravascular transport form of cholesterol, can exist in crystal, liquid crystal and liquid states. The physical state of cholesteryl esters at physiologic temperatures may be a determinant of their pathogenicity. This review has surveyed saturated aliphatic cholesteryl esters of chain length 1 to 24 carbons and a series of medium-chained unsaturated cholesteryl esters from chain lengths 14 to 24 carbons. A systematic study of transition temperatures by polarizing microscopy and enthalpies by differential scanning calorimetry has provided unifying concepts concerning the phase behavior as a function of chain length and unsaturation. Neat cholesteryl esters show chain-length dependence of transition temperature and enthalpy of both the crystal and liquid crystal transitions. Double bond position along the fatty acyl chain affected stability of the liquid crystal phases; a smectic phase was not observed for any cholesteryl ester with a double bond more proximal than delta 9. 13C NMR spectroscopy in the isotropic liquid phase has provided evidence suggesting a balance of ring-ring vs. chain-chain interactions as a determinant for isotropic liquid----cholesteric vs. isotropic liquid----smectic transitions. Specifically, anisotropic molecular motions of the steroid ring are greater for cholesteryl esters forming a cholesteric phase than a smectic phase from the melt. Chain-chain interactions apparently predominate in smectic phase formation. The X-ray diffraction patterns of cholesteryl esters as a function of chain length reveal several isostructural series and known single crystal data are presented. A chain length depending on the periodicity of the smectic phase is observed which may be different for saturated vs. unsaturated esters. In summary, the phase behavior of cholesteryl ester molecules is complex and cannot be determined a priori from the phase behavior of component cholesterol and fatty acid. The data presented here should provide insight into the biological behavior of this lipid class.
Calorimetry, Differential Scanning↗
Interactions of myristic acid with bovine serum albumin: a 13C NMR study.
Interactions of myristic acid with bovine serum albumin were studied by 13C NMR spectroscopy at 50.3 MHz using 90% isotopically substituted [1-13C]-, [3-13C]-, and [14-13C]myristic acids, either individually or in a combination of all three with albumin. At pH 7.4, two or more resonances of different intensities were observed for each 13C-enriched myristic acid. Carboxyl and methylene C-3 resonances corresponding to the major myristic acid environment(s) exhibited pH-dependent chemical shift changes indicative of protonation below pH 6.7; in contrast, carboxyl groups in minor environments were resistant to protonation. 13C NMR spectra obtained as a function of the molar ratio of [3-13C]- and [14-13C]myristic acid to bovine serum albumin (from 0.7 to 5.6) revealed at least two narrow resonances for each carbon at all molar ratios. Thus, bovine serum albumin binding sites for myristic acid are heterogeneous with respect to titration behavior and with respect to the local magnetic environment at both the polar and the nonpolar ends of the fatty acid. The narrow resonances observed for the methylene and methyl carbons are inconsistent with complete immobilization of the protein-bound acid molecules. Together with spin- lattice relaxation times and nuclear Overhauser enhancements, the linewidth results indicate that bound myristic acid has internal motions that are rapid compared with overall protein tumbling and that the C-3 methylene carbon is more restricted than the terminal methyl carbon.
Binding Sites↗
Physicochemical and histological changes in the arterial wall of nonhuman primates during progression and regression of atherosclerosis.
To identify the temporal changes occurring during progression and regression of atherosclerosis in nonhuman primates, we have studied the physicochemical and histological characteristics of arterial wall lesions during a 30-mo progression period of diet-induced hypercholesterolemia and during a 12-mo period of regression. Three groups of cynomolgous monkeys (Macaca fascicularis) were studied. Control groups were fed a basal chow diet for 18, 24, and 30 mo and were compared with progression groups that were fed a high-cholesterol-containing diet for up to 30 mo. Regression groups were fed a high-cholesterol diet for 18 mo to induce atherosclerosis and then fed monkey chow for up to 12 mo. The progression group monkeys were killed at 6, 12, 18, 24, and 30 mo, and the regression animals were killed at 24 and 30 mo (i.e., after 6 and 12 mo of being fed a noncholesterol-containing chow diet). Histology and morphometry, physical microscopy for cholesterol monohydrate crystals, foam cell and droplet melting points and chemical composition studies were completed on a large number of individual arterial lesions. Control animals had very little cholesterol ester, rare foam cells, and no extracellular cholesterol ester droplets or cholesterol crystals. During progression, the arteries first increased cholesterol ester content to produce high melting (approximately 45 degrees C) foam cell-rich lesions essentially devoid of cholesterol crystals. With time, the number of cholesterol crystals increased so that by 30 mo large numbers were present. Foam cells decreased with time but their melting temperature remained high while that of extracellular droplets fell to approximately 38 degrees C. Between 18 and 30 mo necrosis appeared and worsened. After 6-mo regression, unexpected changes occurred in the lesions. Compared with 24-mo progression, the chemical composition showed a relative increase in free cholesterol, a decrease in cholesterol ester and microscopy revealed large numbers of cholesterol crystals. Concomitantly, foam cells decreased and the melting temperature of both intra- and extracellular cholesterol ester markedly decreased. After 12-mo regression cholesterol decreased, cholesterol crystals and necrosis diminished and collagen appeared increased. Thus, during progression there is initially an increase in the number of foam cells containing very high-melting intracellular cholesterol ester droplets. By 30 mo, cholesterol crystals and necrosis dominate and high-melting foam cells appear only at lesion margins, suggesting that the initial process continues at the lesion edge. The lower melting point of extracellular esters indicates a lipid composition different from intracellular droplets. Thus, the changes observed in these animals generally reflect those predicted for progression of human atherosclerosis. During the initial 6 mo of regression, necrosis remains, the number of foam cell decreases, and cholesterol ester content decreases; however the relative proportion of free cholesterol content increases, and large numbers of cholesterol content are formed. Thus, large and rapid decreases in serum cholesterol concentration to produce regression in fact may result in the precipitation of cholesterol monohydrate and an apparent worsening of the lesions. More prolonged regression (12-mo) tends to return the lipid composition of the artery wall towards normal, partially reduces cholesterol crystals, and results in an improved but scarred intima.
Animals↗
Identification and detection of in situ cellular and regional differences of lipid composition and class in lipid-rich tissue using hot stage polarizing light microscopy.
To determine whether in situ tissue lipid characterization is possible, we examined carefully prepared frozen sections from a variety of lipid-rich tissues of the cholesterol-fed rabbit by hot stage polarizing light microscopy and conventional histologic staining. Heating of frozen sections to less than 60 degrees C did not affect tissue architecture or staining characteristics making pathologic and physical chemical correlations possible. The melting temperatures of cholesterol ester inclusions in individual foam cells in rabbit atherosclerotic lesions and adrenal gland could be determined as well as the melting characteristics of crystals and triglyceride in these and other tissues. Differential scanning calorimetry and polarized light transmittance were used to confirm melting temperatures determined by microscopy. Combining data from histologic staining, polarizing light microscopy, and the thermal characteristics of lipid enables the various lipid classes to be identified within individual cells. Differences in melting temperatures between lipids of the same class give indications of the degree of saturation of the lipids. Regional differences of cholesterol ester-melting temperatures in the chow-fed rabbit adrenal cortex were detected which implied differences in chemical composition. Cholesterol feeding raised the melting temperature and tended to abolish the marked regional differences in melting temperature of the cholesterol esters in the adrenal cortex. Rabbit atherosclerotic lesions, induced by balloon deendothelialization and cholesterol feeding, revealed differences in foam cell-melting temperatures within the same lesion. Melting temperatures of cholesterol ester deposited in the liver were more uniform. Each tissue studied revealed distinctly different cholesterol ester-melting characteristics.
Adipose Tissue↗
Physicochemical characterization of the urinary lipid from humans with nephrotic syndrome.
The aim of this study was to investigate the nature of urinary lipid in humans with nephrotic syndrome. Fresh urine specimens were fractionated by centrifugation into a lower cellular fraction and an upper noncellular fraction. Of the 11 urine specimens examined, six cellular fractions contained cells (oval fat bodies) that were laden with anisotropic (birefringent) droplets when viewed by polarizing microscopy. The mean total cholesterol excretions for the five urine specimens without anisotropic droplets and the six urine specimens with anisotropic droplets were 8.7 mg/L and 35.5 mg/L, respectively. The cellular fractions of the six urine specimens with anisotropic droplets are enriched in cholesterol esters relative to whole urine. Upon heating, the anisotropic droplets underwent phase transitions characteristic of cholesterol esters, as observed by polarizing microscopy. The mean cholesteric to isotropic phase transition temperature of the anisotropic droplets was 41.3 degrees C. These data indicate that the anisotropic droplets of the oval fat bodies were composed of cholesterol esters acylated largely with monounsaturated fatty acids consistent with cellular origin. The noncellular fractions were subjected to ultracentrifugation (48,000 X g for 2 hours) and then separated into supernate and infranate fractions. The supernate fractions contained minor amounts of lipid, except in two cases of massive lipiduria. In these two cases, the supernate fractions contained many individual anisotropic droplets with lipid composition nearly identical to their cellular fractions. The dispersed lipid of the infranate fractions were invisible by microscope. Nine of the 11 infranate fractions revealed an alpha migrating lipid band by agarose gel electrophoresis. For urine specimens with anisotropic droplets, the infranate fractions contained cholesterol ester fatty acids that were less saturated (as measured by gas-liquid chromatography) than the cellular fractions. Thus, the cholesterol esters of the infranate fractions were derived from a different source (probably high-density lipoproteins) than the cholesterol esters of the cellular fractions.
Adolescent↗
Surface-to-core and interparticle equilibrium distributions of triglyceride-rich lipoprotein lipids.
The phase equilibria of human very low density lipoprotein (VLDL) and monkey chylomicron lipids was examined. Triglyceride (TG), cholesterol ester (CE), and cholesterol (C) partitioned into both surface monolayer and oil "core" phases of emulsions of lipoprotein lipids, whereas phospholipid was found exclusively in the surface. In addition to phospholipid, the surface lipids consisted of 2-4% (by weight) TG, less than 1% CE, and 22% C (VLDL), 5-8% C (chylomicrons). The oil lipids consisted mainly of TG, but also 13-16% CE (VLDL), 3% CE (chylomicrons), and 1-2% C (VLDL), 0.3-0.4% C (chylomicrons). The equilibrium state of lipids within size subfractions of native lipoproteins was defined using phase diagram analysis. Subfractions were in equilibrium with respect to surface-to-core and interparticle distributions of C molecules. In contrast, subfracitions were not in a state of interparticle TG and CE equilibrium. By using the phase diagrams, the percentages of the total particle lipids carried in the phases of lipoproteins of varying size were calculated. For Sf greater than 400 particles, greater than or equal to 30% of the total particle C molecules are carried in the core, and less than 3% of the TG and CE molecules are located in the surface. Nascent, plasma, remnant, and beta-migrating TG-rich lipoprotein compositions taken from the literature were compared using phase diagrams. Although the total compositions of nascent liver VLDL and lymph chylomicrons vary substantially, they have identical concentrations of C in their respective phases. Upon equilibration with plasma, the surface and core of nascent TG-rich lipoproteins become enriched (2-4-fold) with C. Remnants and beta-VLDL have the most C-rich phases of the TG-rich lipoproteins examined. The analysis indicates that the C concentrations of the phases of a lipoprotein are related to its metabolic status.
Animals↗
Solubilization of triolein and cholesteryl oleate in egg phosphatidylcholine vesicles.
The incorporation of cholesteryl oleate and triolein into phospholipid vesicles was studied in cosonicated mixtures of 94 weight % egg phosphatidylcholine and 6 weight % neutral lipid (0-6% triolein and 6-0% cholesteryl oleate). 13C NMR spectroscopy was used to quantitate both neutral lipids in vesicles containing 90% isotopically substituted [carbonyl-13C]cholesteryl oleate and [carbonyl-13C]triolein. Vesicles were also prepared with radiolabeled cholesteryl oleate and triolein and the composition of ultracentrifugal subfractions determined by chemical and radioisotopic methods. For a given starting composition, the incorporation of neutral lipids into vesicles was similar for vesicles prepared and analyzed by the two methodologies. The maximum solubility in vesicles prepared at 55 degrees C with a single neutral lipid was 3.1 weight % triolein (2.8 mol %) and 2.3 weight % cholesteryl oleate (2.8 mol %). In sonication mixtures with both triolein and cholesteryl oleate, the incorporation of each lipid into vesicles was proportional to the starting concentration; the total incorporation of neutral lipid was less than or equal to 4.0% (weight or mole per cent). The solubility limits were intermediate between the theoretical cases of complete additivity and complete competition. The [13C]carbonyl chemical shifts showed that the carbonyl groups of the vesicle-solubilized neutral lipids were close to the vesicle surface and that excess triolein and cholesteryl oleate partitioned into an oil phase containing both triolein and cholesteryl oleate.
Cholesterol Esters↗
Interactions of the carboxyl group of oleic acid with bovine serum albumin: a 13C NMR study.
The interactions of the carboxyl group of oleic acid with bovine serum albumin (BSA) were studied by 13C NMR spectroscopy at 50.3 MHz using 90% isotopically substituted [1-13C]oleic acid. 13C NMR spectra were obtained as a function of the mole ratio of oleic acid to BSA (from 0.5-10.0) and, for selected mole ratios, as a function of pH (between pH 3.0 and 10.6) and temperature (between 15 and 55 degrees C and thermally denatured at 95 degrees C). Except for spectra of highly acidic (pH less than or equal to 3.9) and denatured samples, spectra of oleic acid/BSA complexes showed multiple narrow resonances from the oleic acid carboxyl carbon in a region (179-184 ppm) downfield from protein carbonyl and carboxyl carbon resonances. At low oleic acid/BSA ratios (0.5 and 1.0), at least two oleic acid carboxyl carbon peaks were observed; at high ratios (greater than or equal to 3.0), at least four peaks were present. The intensities of individual peaks, but not their chemical shifts, varied with the oleic acid/BSA ratio. The chemical shift of individual oleic acid peaks was invariant between pH 6.0 and 10.6; below pH 6.0, one of the oleic acid resonances exhibited an NMR titration curve with an apparent pKa of approximately 4. Thus, BSA binding sites for oleic acid are heterogeneous as monitored by the magnetic microenvironment of the oleic acid carboxyl carbon. The number of different oleic acid environments and the relative population of oleic acid molecules in these environments is dependent on the mole ratio of oleic acid/BSA. Our results suggested that the anionic form of oleic acid is bound to BSA at physiological pH and that the multiplicity of NMR peaks for [1-13C]oleic acid resulted from, at least in part, different electrostatic and hydrogen bonding interactions between the oleic acid carboxyl group and specific amino acid residues of BSA.
Fourier Analysis↗
Cholesterol content of red blood cells and low-density lipoproteins in hypertriglyceridemia.
The red blood cells and the low-density lipoproteins in hypertriglyceridemia have a lower ratio of unesterified cholesterol to phospholipid than normal. The low-density lipoproteins are also smaller and more dense in hypertriglyceridemia, and contain only 45% of the normal unesterified cholesterol mass. The phase behavior of the lipids shows that normal red cells and low-density lipoproteins are close to saturation with cholesterol, whereas in hypertriglyceridemia less cholesterol is present. Because newly secreted triacylglycerol-rich lipoproteins are poor in cholesterol, their excess production and transport in hypertriglyceridemia may prevent maintenance of the normal cholesterol content of blood cells and low-density lipoproteins. Partitioning of cholesterol into triacylglycerol-rich lipoproteins is able to account for significant fluxes of unesterified cholesterol in the plasma compartment.
Cholesterol↗
1H NMR studies of lymph chylomicra and very low density lipoproteins from nonhuman primates.
1H NMR spectroscopy at 200 MHz was used to study triglyceride crystalline leads to liquid transitions which occurred on heating between 10 and 50 degrees C in very low density lipoprotein and subfractionated chylomicron particles from nonhuman primates fed a saturated fat (butter fat) diet. Model system studies of pure triglycerides (triolein, tripalmitin and a 1:1 mixture) and emulsion particles consisting of these triglycerides with a surface of egg phosphatidylcholine showed that high resolution spectra were obtained only from liquid triglycerides. In lipoprotein spectra, changes in 1H NMR peak intensities and line widths accompanied the solid leads to liquid transition of the constituent triglycerides. Peak areas of fatty acyl resonances were proportional to the percentage of melted triglyceride determined by differential scanning calorimetry. NMR peak area measurements showed that the calorimetric transition involved the melting of relatively greater numbers of saturated fatty acyl chains than unsaturated chains; at temperatures well below the solid leads to liquid transition, the lipoproteins contained a significant fraction (approximately 33%) of liquid triglycerides which were relatively enriched in unsaturated fatty acyl chains. For model systems containing mixtures of solid and liquid triglycerides, the temperature dependence of line widths of fatty acyl resonances demonstrated that solid triglycerides decreased the mobility of the liquid triglycerides. A similar temperature dependence for the lipoprotein resonances suggested that solid and liquid species are co-mixed in individual lipoprotein particles within a purified subfraction. Temperature-dependent line width and intensity changes were observed for the phospholipid-choline methyl resonance in lipoprotein spectra and were apparently independent of the core transition.
Animals↗