Fluorescence study of the motional states of core and surface lipids in native and reconstituted low density lipoproteins.
Low density lipoproteins (LDL) consist of an apolar core of cholesterol esters and triglycerides surrounded by a monolayer of phospholipid, cholesterol, and a single molecule of apolipoprotein B (apoB-100). To determine the influence of core and surface constituents on the surface of LDL, we have measured core and surface order parameters for native LDL, and reconstituted LDLs (rLDL) whose apolar core lipids were extracted and replaced with either cholesterol oleate (CO) or triolein (TO). Order parameters were measured by fluorescence depolarization of diphenylhexatriene (DPH), which is located primarily in the core, and of trimethylammoniumdiphenylhexatriene (TMA-DPH), which is anchored at the water-phospholipid interface. DPH order parameters for LDL reconstituted with TO (r-[TO]LDL) were much lower than those for LDL reconstituted with CO (r-[CO]LDL), consistent with the physical properties of TO, a nonviscous liquid at all temperatures studied, and CO, which exists in a liquid crystalline or viscous liquid state at the temperatures studied. Although core cholesterol esters in r[CO]LDL and native LDL undergo distinct order-disorder transitions, these transitions were not detected by DPH. This is most likely due to the difference between the time scale for end-over-end tumbling of cholesterol esters and the fluorescence lifetime of DPH. Despite the fact that the core lipids of r-[CO]LDL were much more ordered than those of r-[TO]LDL, surface order parameters for both lipoproteins were similar. We conclude that the motional states of the core and surface lipids are relatively independent. Surface order parameters for native LDL were higher than those for reconstituted LDLs.(ABSTRACT TRUNCATED AT 250 WORDS)
Kroon
P A
PA
Department of Biochemistry, University of Queensland, Brisbane, Australia.
D002788:Cholesterol Esters / Q000737:chemistry; D004161:Diphenylhexatriene / Q000031:analogs & derivatives / Q000737:chemistry; D005454:Fluorescence Polarization; D006801:Humans; D008055:Lipids / Q000737:chemistry*; D008077:Lipoproteins, LDL / Q000737:chemistry*; D014304:Triolein / Q000737:chemistry
D002788:Cholesterol Esters; D008055:Lipids; D008077:Lipoproteins, LDL; D014304:Triolein; D004161:Diphenylhexatriene; C014409:cholesteryl oleate; C033628:1-(4-(trimethylamino)phenyl)-6-phenylhexa-1,3,5-triene