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|Title:||Phospholipid Transfer From Vesicles to High Density Lipoproteins, Catalyzed by Human Plasma Phospholipid Transfer Protein (Liposome)|
|Author(s):||Sweeny, Susan Anita|
|Department / Program:||Biochemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Human plasma phospholipid transfer protein (PLTP) catalyzes the mass transfer of phosphatidylcholine (PC). Partial purification of PLTP yielded proteins with apparent M(,r) = 59,000 and 40,000 by SDS-PAGE. PLTP activity was measured by transfer of ('14)C L-(alpha)-dipalmitoyl PC from egg-PC vesicles to HDL. Activity was enhanced at low pH (4.5) and upon addition of (beta)-mercaptoethanol while Ca('+2) and Na('+) had no effect. E(,act) for facilitated PC transfer was 18.2 (+OR-) 2 kcal/mol.
The donor specificity of PLTP was examined using vesicles containing egg-PC plus cholesterol or sphingomyelin. The fluidity of the donor membrane (measured by fluorescence polarization of diphenylhexatriene) correlated strongly with a decrease in PLTP activity. Phosphatidic acid did not affect activity. Increase in vesicle size reduced activity.
The acceptor specificity of PLTP was examined using chemically modified HDL. PLTP activity increased up to 1.7-fold with an initial increase in negative charge and then decreased upon extensive modification.
The association of PLTP with its substrates was examined by gel filtration chromatography. PLTP associated with donor vesicles but not with holo HDL although holo HDL and HDL apolipoproteins were able to remove PLTP from the vesicles. Citraconylated HDL removed even more PLTP from the vesicles and inhibited PLTP activity. Calcium prevented this inhibition by modified HDL and actually enhanced PLTP activity 2-fold over the level of native HDL. It also prevented removal of PLTP from the vesicles.
A mechanism is proposed where PLTP binds to vesicles and enhances the diffusion of PC into the medium where it is adsorbed by HDL.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.
|Date Available in IDEALS:||2014-12-15|