Interaction of bilirubin with lipids studied by fluorescence quenching method

The interaction of bilirubin and various lipids was studied by a static fluorescence quenching method. A quenching equation was developed to determine the binding constant. This method was tested first by a 5-dimethylaminoaphthalene-1-sulfonyl (dansyl).bovine albumin system and then applied to a fluorescent probe containing lipid. Both systems can yield binding parameters. For certain lipid systems, some dynamic quenching was observed at the part of the curve where bilirubin concentrations were at the extreme. Of the lipids tested, sphingomyelin showed the highest association constant; this may be related to the central nervous system toxicity of this bile pigment. The association constants determined with pure lipids were 2.4 x 10(5) M-1 for phosphatidylserine; 3.7 x 10(6) M-1 for sphingomyelin; 2.4 x 10(6) M-1 for diphosphatidylcholine with 5% cholesterol; 9.8 x 10(5) M-1 for diphosphatidycholine alone; 2.2 x 10(5) M-1 for phosphatidylethanolamine; and 1.6 x 10(5) M-1 for diphosphatidylglycerol (cardiolipin); and those with mixed lipids were 4.2 to 5 x 10(5) M-1 for total brain lipid if cow and 3 to 3.6 x 10(5) M-1 for total skin lipid of pig.