Transfer of bovine J-blood-group determinant onto erythrocytes: Isolation and identification of a blocker

The bovine J‐blood‐group determinant is transferred from a serum glycoprotein to an erythrocyte membrane lipid by incubation in vitro. This transfer is inhibited by a lipid (called ‘blocker’) occurring in bovine and human serum, in other bovine and human tissues, yeast and plant tissues. The blocker was isolated from bovine spleen and identified as phosphatidylserine. Moreover, phosphatidylinositol acts as a blocker, while a variety of other phospholipids, glycosphingolipids and neutral lipids have no function as blockers. Mild alkaline deacylation deletes the blocker activity of both phosphatidylserine and phosphatidylinositol. Methyl esters of these phospholipids, or exchange of the amino group for a hydroxyl group in phosphatidylserine or N‐benzoylation of phosphatidylserine, do not affect the blocker function. The blocker function of phosphatidylinositol is lost after periodate oxidation. The blocker reacts with the J‐containing serum protein, not with the erythrocyte membrane. After preincubation of the J‐positive serum protein with the blocker and reextraction of excess blocker, the serum protein remains J‐positive, but is then unable to transfer the J determinant to the erythrocyte membrane.