Fluorescence quenching by iodide ions of low density lipoproteins from normolipidemic and hypercholesterolemic type II a subjects. Effect of low density lipoprotein-cholesterol and low density lipoprotein non-apolipoprotein-B

Abstract

In order to evaluate the effect of hypercholesterolemia on the surface properties of low density lipoproteins (LDL), the quenching by iodide ions of the native fluorescence of human plasma LDL was studied on normolipidemic and hypercholesterolemic type II a subjects. A significant difference ( P < 0.001) was found between these two groups (20 patients with type II a hyperlipoproteinemia, 18 normolipidemic subjects). Furthermore, the fluorescence quenching ( F 0 − F 1) F 0 ( F 0 and F 1 fluorescence intensity respectively in the absence and in the presence of iodide ions is negatively correlated with the relative LDL-cholesterol level (LDL-cholesterol/LDL-apoprotein). In contrast, this quenching is positively correlated with the relative LDL-non-apo-B level (LDL-non-apo-B/LDL apo). It is suggested that the greater the LDL-cholesterol level, the more embedded are the tryptophyl residues in the hydrophobic core. In contrast, the greater the LDL-non-apo-B level, the more exposed are the tryptophyl to the aqueous environment. Thus, a significant conformation change of the superficial apolipoproteins occurs, which could affect the immunological properties of the LDL and their affinity to the LDL receptors.