The visibly fluorescent phospholipids of serum lipoproteins

The blusih-white fluorescence exhibited by lipoproteins from human serum has been investigated. It appears that high-density lipoprotein (HDL), low-density lipoprotein (LDL), and very low density lipoprotein (VLDL) all exhibit this fluorescence with excitation maximum at about 360 nm and fluorescence maximum at about 450 nm. The fluorescence resides in the phospholipid fraction of the lipoproteins and is not located in the fatty acids, since the water-soluble deacylated phospholipid fraction exhibited the same fluorescence. Upon electrophoresis of this fraction at pH 6.5 the fluorescent material carried a negative charge and moved a distance similar to glycerophosphoserine and glycerophosphoinositol, which both carry one negative charge. This negatively charged fluorescent product is ninhydrine negative, and gives a positive reaction for phosphate esters and 1,2-glycols. The detailed structure of the fluorescent product is not yet known. It is suggested that reactive aldehydes are involved in its formation from the aminophosphatides. Its possible relationship to tissue peroxidation is discussed.