Ganglioside from eel serum high density lipoprotein (HDL) and its role as a ligand for HDL binding protein.

First, we attempted to isolate glycosphingolipids from eel serum HDL. A single ganglioside containing N-acetylneuraminic acid (NeuAc), which is positive with resorcinol and orcinol reactions, was purified. The mobilities of the purified ganglioside and its lyso-form on high performance TLC were similar as those of authentic GM4 and its lyso-form, respectively. The mass of the purified ganglioside was determined by TOF mass spectrometer, and the mass of its oligosaccharide was the same as that of authentic GM4 from human brain consisting of disaccharide of NeuAc and galactose. The ganglioside from eel HDL was not hydrolyzed by recombinant endoglycoceramidase II, which cannot hydrolyze between galactose and ceramide of gangliosides, but hydrolyzes between glucose and ceramide. We concluded from these results that the ganglioside purified from eel serum HDL is GM4. Second, we investigated the effects of the ganglioside on binding of HDL labeled with fluorescein isothiocyanate (FITC-HDL) to cultured eel hepatocytes and on FITC-HDL ligand blotting by using plasma membrane proteins of the hepatocytes. Stimulatory effect of GM4 on FITC-HDL binding to the hepatocytes and FITC-HDL ligand blotting suggests strongly that GM4 is a ligand for HDL binding protein of eel hepatocytes.