ALPHA-LACTALBUMIN INDUCES BOVINE-MILK BETA-1,4-GALACTOSYLTRANSFERASE TO UTILIZE UDP-GALNAC

We now report that alpha-lactalbumin (alpha-LA) has a novel effect on bovine milk UDP-Gal:GlcNAc-beta 1,4 galactosyltransferase (beta 1,41-GT) and induces the enzyme to efficiently utilize UDP-GalNAc as a donor. In the presence of alpha-LA the enzyme transfers GalNAc to free GlcNAc to produce GalNAc beta 1-4GlcNAc at a rate 55% of that compared to the rate when UDP-Gal is the donor in the absence of alpha-LA. The stimulation by alpha-LA is dependent on the concentrations of alpha-LA, acceptor, and sugar nucleotide. Interestingly, beta 1,4-GT is unable to transfer GalNAc to Glc with or without alpha-LA. alpha-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 beta 1,4-GT has an inherent ability to utilize two different sugar nucleotides and the sugar nucleotide preference is regulatable by alpha-LA.