Fluorescence lifetime distributions of diphenylhexatrienylpropionyl-labeled phospholipids in atherogenic lipoproteins

摘要

Fluorescent analogs of phosphatidylcholine (PC) and sphingomyelin (SM) were prepared and incorporated into the surface layer of human low density lipoprotein (LDL) and lipoprotein (a) [Lp(a)]. Diphenylhexatrienylpropionic acid (DPH) was covalently linked to PC (DPH-PC) and SM (DPH-SM). Fluorescence lifetimes of the labeled lipoproteins were determined by phase and modulation fluorometry. We found bimodal Lorentzian distributions for the decay times of DPH-PC and DPH-SM in LDL and Lp(a). Lifetime distribution centers for labeled lipids were very similar except for DPH-PC in Lp(a) which was shifted to longer lifetimes. Thus, PC experiences a less polar environment in Lp(a) than in LDL. The distributional width of DPH-PC in Lp(a) was broader than in LDL. Accordingly, phosphatidylcholine must be localized in a much more homogeneous environment in LDL as compared with Lp(a). On the other hand, no difference in distributional widths was observed for DPH-SM in both lipoproteins, showing that SM organization in Lp(a) is unaffected by ape(a). From the obtained fluorescence data we propose that apoprotein B preferentially associates with phosphatidylcholine.