Fluorescence studies of protein-sterol relationships in human plasma lipoproteins

Cholesta-5,7,9(11)-trien-3beta-ol and its oleate ester were incorporated into human low-density lipoprotein and reconstituted high-density lipoprotein. The unesterified sterol was more efficient than its ester in quenching tryptophan fluorescence, especially in low-density lipoprotein. The results, which indicate that in such lipoproteins unesterified sterols are more closely associated with peptide than are esterified sterols, are used to assess possible structures for the lipoproteins.