α-Lactalbumin (α-LA) is a regulatory protein by which the mammalian β1,4-galactosyltransferase (β1,4-galT) is induced to utilize glucose as an acceptor instead of N-acetylglucosamine (GlcNAc) during lactose synthesis in mammary gland. α-LA can also modulate β1,4-galT to utilize UDP-N-acetylgalactosamine (UDP-GalNAc) as a donor towards GlcNAc acceptor substrate with high efficiency in vitro [Do, Do and Cummings (1995) J. Biol. Chem. 270, 18447-18451]. In the present study we transfected cDNA encoding bovine α-LA into Lec8 cells and examined whether nucleotide sugar switching of UDP-galactose (UDP-Gal) into UDP-GalNAc occurred in vivo and whether the neo-glycosylation of GalNAcβ1,4GlcNAc-R structure was synthesized in α-LA-stable transfectants. Our studies demonstrate that the stable expression of α-LA in Lec8 cells induces the formation of GalNAcβ1,4GlcNAc-R in vivo through the nucleotide sugar switching of β1,4-galT.

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