α-Lactalbumin induces bovine milk β1,4-galactosyltransferase to utilize UDP-GalNAc

Abstract

We now report that α-lactalbumin (α-LA) has a novel effect on bovine milk UDP-Gal:GlcNAc-β1,4-galactosyltransferase (β1,4-GT) and induces the enzyme to efficiently utilize UDP-GalNAc as a donor. In the presence of α- LA the enzyme transfers GalNAc to free GlcNAc to produce GalNAcβ1-4GlcNAc at a rate 55% of that compared to the rate when UDP-Gal is the donor in the absence of α-LA. The stimulation by α-LA is dependent on the concentrations of α-LA, acceptor, and sugar nucleotide. Interestingly, β1,4-GT is unable to transfer Gal-NAc to Glc with or without α-LA. α-LA also stimulates the transfer of GalNAc from UDP-GalNAc to various chitin oligomers, although the degree of stimulation decreases as the acceptor size increases. Thus, bovine milk β1,4-GT has an inherent ability to utilize two different sugar nucleotides and the sugar nucleotide preference is regulatable by α-LA.