1 May 1990 Rotational diffusion of the low-density lipoprotein-receptor complex
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Time-resolved phosphorescence anisotropy. has been used to assess the rotational dynamics of human serum lipoproteins labeled with phosphorescent probes of high triplet yield. Covalent labeling of apolipoprotein B with erythrosin revealed the existence of segmental motion of labeled domains within the particle as well as global rotation of the particles. The binding of the low density lipoprotein to cell surface receptors resulted in a freezing of the global motion but the maintenance of faster motion of domains within the apolipoprotein. Labeling of the lipid phase of the low density lipoproteins with an eosinyl fatty acid also revealed the existence of two motions. The shorter time constant was attributed to the motion of the chromophore within the lipoprotein particle, while the longer time constant represented the global tumbling of the particle in solution. To examine the the physical state of the lipid phase in lipoproteins, the steady-state fluorescence anisotropy of n-(9-anthroyloxy) fatty acids was examined in microemulsions and phospholipid bilayers. The phase transition in the surface monolayer of the microemulsion is significantly less cooperative than the same transition in a bilayer vesicle. Moreover, the rate at which cholesterol transfers from a donor structure to an acceptor is much faster for the microemulsion than for the bilayer vesicle. These results indicate differences in the packing of phospholipids in the monolayer of the microemulsion as compared to the external leaflet of the bilayer vesicle.
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Leann M. Tilley, Q. T. Li, William H. Sawyer, John R. Morrison, Noel H. Fidge, "Rotational diffusion of the low-density lipoprotein-receptor complex", Proc. SPIE 1204, Time-Resolved Laser Spectroscopy in Biochemistry II, (1 May 1990); doi: 10.1117/12.17740; https://doi.org/10.1117/12.17740

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