Journal of Lipid Research, Vol 28, 332-337, Copyright © 1987 by Lipid Research, Inc.
Tetranitromethane modification of human high density lipoprotein (HDL3): inactivation of high density lipoprotein binding is not related to cross-linking of phospholipids to apoproteins
GK Chacko, S Lund-Katz, WJ Johnson and JB Karlin
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)
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