STRUCTURAL CHARACTERIZATION OF INTERMEDIATES IN THE BIOSYNTHETIC-PATHWAY OF NEOLACTO GLYCOSPHINGOLIPIDS - DIFFERENTIAL EXPRESSION IN HUMAN LEUKEMIA-CELLS

The biosynthesis of neolacto glycosphingolipids is thought to proceed via reactions catalysed by the two enzymes beta 1-3-N-acetylglucosamin yltransferase (beta 1,3GlcNAcT) and beta 1-4 galactosyltransferase (be ta 1,4GalT). In general, only the products of the latter enzyme have b een isolated from tissues and structurally characterized. Among the Gl cNAc beta 1-3-R glycosphingolipids, only lactotrioasylceramide (Lc(3)C er, the initial product in the biosynthesis of neolacto glycosphingoli pids) has been isolated and structurally characterized. Longer-chain g lycosphingolipids with a terminal GlcNAc-beta 1-3-R structure are cons idered to be intermediates in the synthesis of complex neolacto glycos phingolipids. We have detected a series of GlcNAc beta 1-3-R glycosphi ngolipids in extracts obtained from human leukocytes isolated from pat ients with leukaemia using a monoclonal antibody (TE5) which specifica lly recognizes these compounds. The structures of three of these compo unds purified from chronic myelocytic leukaemia (CML) cells have been determined using a combination of enzymatic, immunostaining and chemic al methods. The compounds were found to have the following structures: GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer (Lc(3)Cer) GlcNAc beta 1-3 Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer (nLc(5)Cer) Glc NAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer (nLc(7)Cer) A longer-chain compound, apparentl y nLc(9)Cer, was also detected. TLC immunostaining analysis of glycosp hingolipids isolated from cells obtained from patients with various le ukaemias demonstrated that GlcNAc beta 1-3-R glycosphingolipids have a distribution that depends on the stage of differentiation and lineage of the cell population. These results are discussed in relation to th e regulated expression of neolacto glycosphingolipids among human leuk ocyte populations.