Tetranitromethane modification of human high density lipoprotein (HDL3): inactivation of high density lipoprotein binding is not related to cross-linking of phospholipids to apoproteins.
Treatment of human high density lipoprotein (HDL) with tetranitromethane (TNM) inhibits its binding to HDL-specific binding sites of cells and isolated membranes. The mechanism of this inhibition, however, is not known; during treatment of HDL with TNM, in addition to the expected nitration of tyrosine residues, cross-linking of lipids to apoproteins and of apoproteins to one another occurs. In order to determine whether the cross-linking of lipids to apoproteins occurs through the carbon-carbon double bonds in the acyl chains, and to determine whether the cross-linking of phospholipids to apoproteins is a possible mechanism of inhibition of binding, we have prepared a reconstituted HDL3 in which the native phospholipids were replaced with dimyristoyl phosphatidylcholine (DMPC). As a control, a reconstituted HDL3 (C-r-HDL3) was also prepared using the total apoproteins and the total lipid constituents of native HDL3. The reconstituted DMPC-containing HDL3 (DMPC-r-HDL3) was similar to native HDL3 and to C-r-HDL3 in its agarose gel electrophoretic mobility, in its chemical composition, and in its binding to rat liver plasma membranes. When treated with TNM, DMPC-r-HDL3, like the native HDL3 and C-r-HDL3, lost its ability to bind to the HDL binding sites of rat liver plasma membranes, as determined by competitive binding assays with 125I-labeled human HDL3 as the tracer. Nitrated DMPC-r-HDL3 contained only traces of phospholipids covalently linked to apoproteins, whereas 21-26% of the total phospholipids were cross-linked to apoproteins of nitrated C-r-HDL3 and nitrated native HDL3.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D001059:Apoproteins / Q000378:metabolism; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008075:Lipoproteins, HDL / Q000378:metabolism*; D053440:Lipoproteins, HDL3; D008099:Liver / Q000378:metabolism; D008297:Male; D010743:Phospholipids / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D013774:Tetranitromethane
D001059:Apoproteins; D008075:Lipoproteins, HDL; D053440:Lipoproteins, HDL3; D010743:Phospholipids; D013774:Tetranitromethane