William W. Mantulin

Effect of saturated and polyunsaturated fat diets on the composition and structure of human low density lipoproteins

Abstract We have studied the effect of diets of saturated and polyunsaturated fat on the composition, structure and thermal behavior of human plasma low density lipoproteins (LDL). We find that relative to a saturated fat diet one of polyunsaturated fat produces: 1. (1) An increase. in the unsaturated acyl content of all lipid classes of LDL. 2. (2) An increase in the triglyceride content of LDL. 3. (3) A decrease in the temperature of the thermotropic liquid crystal to isotropic liquid phase transition of LDL. 4. (4) No effect on the temperature of LDL denaturation. In spite of major changes in the fatty acid composition of the major lipid of LDL, cholesteryl esters, the thermal properties of LDL are dominated by their triglyceride content. Since a polyunsaturated fat diet raised LDL triglyceride levels, our calorimetric and spectroscopic results suggest that the thermal properties and the structure of LDL at 37°C are sensitive to the composition of dietary fat.

The properties of membranes formed from cyclopentanoid analogues of phosphatidylcholine

We have examined the thermal characteristics and barrier properties of vesicles formed from six analogues of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). These analogues differ from DPPC in that the glycerol backbone has been replaced by each of the diastereoisomeric cyclopentane-1,2,3-triols. All of these compounds have main gel to liquid-crystal phase transition temperatures within 5 Kelvin of DPPC and four possess comparable enthalpies and entropies of transition. For two of the analogous, however, the values of the enthalpy and entropy of transition are more than double that of DPPC. The permeability characteristics and organization (as measured by diphenylhexatriene fluorescence depolarization) of vesicles formed from these two compounds suggest that their large transition enthalpy and entropy result from either a reorganization of the polar head group region during the transition or interdigitation of the acyl chains of opposing monolayers.

THE ELECTRONIC SPECTROSCOPY OF PYRIMIDINES: THE EFFECT OF COVALENTLY BONDED SULFUR ON THE PHOSPHORESCENCE AND ABSORPTION SPECTRA

Abstract— The phosphorescence of uracil, 2‐thiouracil, 2,4‐dithiouracil and 2‐mercaptopyrimidine was studied at 77 K. 2‐Thiouracil and 2,4‐dithiouracil showed phosphorescence quantum yields of 0.65 and 0.1, respectively. The emitting triplet states of these compounds have been assigned as the 3(π, π*) type. The enhancement of spin‐orbit coupling through the involvement of the 3d orbitals on sulfur has been invoked in describing emission characteristics of thiouracils.

Fluorescent cholesteryl esters in the core of low density lipoprotein

Abstract Fluorescent cholesteryl esters with chromophores placed either on the acyl chain (cholesteryl- cis -parinarate), the sterol ring system (5,7,9-cholesteryl oleate), or the side chain (naphthylcholenamide oleate) have been incorporated into the core of low density lipoprotein. The temperature dependence of several fluorescence parameters has been evaluated. An analysis of the fluorescence lifetime components of cholesteryl- cis -parinarate reveals coexisting environments whose proportion varies and reflects the thermotropic reorganization of the core of the particle. An analysis of the motion by dynamic depolarization suggests that the motions of the acyl chains in the core of the particle are highly restricted.

FLUORESCENCE PROBES OF MEMBRANE STRUCTURE AND DYNAMICS

Spectroscopic probes of lipid and membrane structure, as well as lipid-protein interactions, continue to play an important role in the development of our view of the cell in general and the cell membrane in particular. Recent improvements in the design of commercial spectrofluorimeters and related instruments for measuring fluorescence spectra, lifetimes, and polarization have done much to widen the range of systems to which fluorescence spectroscopy may be applied. Several reviews of fluorescence spectroscopy in biological systems have appeared [3,44,52]. Herein, we will cover selected recent developments in the application of fluorescence probe methods to the study of real and model biological membranes. The fluorescence lifetime, spectral distribution, degree of polarization, and fluorescence intensity characterize a fluorophore and its environs. The structural information obtained from a fluorescent probe study include membrane fluidity, the location and movement of specific components within a membrane, conformational changes, charge distributions within membrane components, and changes in membrane potential.

Reversible folding reactions of human apolipoprotein A-I: pressure and guanidinium chloride effects.

Apolipoprotein A-I, the major structural polypeptide of human high-density lipoproteins, activates lecithin: cholesterol acyltransferase, the cholesterol ester-forming enzyme in plasma. Apolipoprotein A-I, like several other apolipoproteins, exhibits structural adaptability, which is manifest in a low free energy of stabilization and facile changes in secondary structure. We have investigated the dual effects of guanidinium chloride (GdmCl) and pressure perturbation at low GdmCl concentrations on apolipoproteins A-I conformational states, using fluorescence detection. Pressure alone (up to 3 kilobar) is insufficient to fully denature apolipoprotein A-I, and results in formation of metastable state(s). However, in conjunction with low concentrations of GdmCl the calculated volume change upon pressure denaturation increases from approx. -50 ml/mol to -90 ml/mol. The free energy of denaturation by pressure perturbation ranges from 1.4 to 1.8 kcal/mol, but the conformational states induced by pressure and GdmCl perturbation are most likely different. The physico-chemical properties of native and pressure-denatured conformational states can be, readily and reversibly, measured by fluorescence techniques. Biological activity of apolipoprotein A-I in the form of lecithin: cholesterol acyltransferase activation, is also reversible upon pressure perturbation. Samples of apolipoprotein A-I exposed to 2 kbar for an hour activated lecithin: cholesterol acyltransferase equally well as controls. To delineate more precisely the conformational states of apolipoprotein A-I under pressure, time-dependent anisotropy decay measurements, capable of resolving rotational heterogeneity, will be required.