Radiation inactivation of binding sites for high-density lipoproteins in human liver membranes.
High-density lipoproteins (HDL) are involved in 'reverse cholesterol transport'. Whether or not cell-surface receptors for HDL exist and participate in this process remains controversial, and part of this controversy has centered on the nature of the HDL binding sites. We therefore used radiation inactivation to determine the molecular mass of the HDL binding sites in human liver membranes in situ. These binding sites, which shared all the characteristics of previously described putative HDL receptors, had a molecular mass of less than 10 kDa, indicating that they are probably not proteins. In addition, the binding of HDL to protein-free liposomes was characterized and was found to display the same affinity (KD = 5 micrograms protein/ml approximately 5.10(-8) M) as that to cell membranes, indicating that HDL binding to cell membranes may not require membrane proteins. These observations highlight an important application of radiation inactivation: the ability to demonstrate that something - in this case, a high-molecular-weight protein that accounts for the majority of the HDL binding activity in human liver membranes - is absent.
Mendel
C M
CM
Cardiovascular Research Institute, University of California, San Francisco 94143-0130.
Kunitake
S T
ST
Hong
K
K
Erickson
S K
SK
Kane
J P
JP
Kempner
E S
ES
D015720:5'-Nucleotidase; D002352:Carrier Proteins; D006801:Humans; D066298:In Vitro Techniques; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008970:Molecular Weight; D009708:Nucleotidases / Q000032:analysis; D016601:RNA-Binding Proteins; D011956:Receptors, Cell Surface / Q000032:analysis* / Q000528:radiation effects; D018110:Receptors, Lipoprotein
D002352:Carrier Proteins; D008075:Lipoproteins, HDL; D016601:RNA-Binding Proteins; D011956:Receptors, Cell Surface; D018110:Receptors, Lipoprotein; C031616:high density lipoprotein receptors; C075197:high density lipoprotein binding protein; D009708:Nucleotidases; D015720:5'-Nucleotidase