Interaction of Apolipoprotein-Alanine and Apolipoprotein-Glutamine-I with Phosphatidylcholine. Effect on Solute Quenching of Intrinsic Fluorescence

The interaction of egg phosphatidylcholine with apoLP-alanine₁, apoLP-glutamine-I, and human serum albumin has been investigated by quenching of the intrinsic protein fluorescence in both the presence and absence of the phospholipid. The quenching by a negatively charged quencher, iodide ion, used in conjunction with a positively charged quencher, pyridinium ion, reflected the relative charge in the region of tryptophans in the protein and indicated the magnitude of binding of phospholipid. Expressions were derived to quantitate both protein accessibility and the phospholipid binding efficiency of these proteins. ApoLP-alanine₁ bound phospholipid more efficiently than apoLP-glutamine-I. Both apolipoproteins were more efficient than human serum albumin.