Exposure of the major human red-cell glycolipid, globoside, to galactose oxidase

Plasma membrane glycolipids are localized at the outer leaflet of the lipid bilayer, and their carbohydrate portions are exposed to the environment. The efficiency of exposure has, however, not been known. We have been able to determine the availability of the major red cell glycolipid, globoside, to externally added galactose oxidase. Red cells were extensively treated with the enzyme and the oxidized cells reduced with NaBD4. After isolation the extent of exposed globoside was estimated by mass spectrometry. The results show that the exposure of globoside varies in red cells of different individuals from 37-66%. The fatty acid composition of externally available globoside was the same as that of non-oxidized globoside. The exposure was not influenced by protease treatment of intact cells and no correlation was found with different ABO blood groups.