Do K Y, Do S I, Cummings R D
Department of Oklahoma Health Sciences Center, Department of Biochemistry and Molecular Biology, Oklahoma City 73190, USA.
J Biol Chem. 1995 Aug 4;270(31):18447-51. doi: 10.1074/jbc.270.31.18447.
We now report that alpha-lactalbumin (alpha-LA) has a novel effect on bovine milk UDP-Gal:GlcNAc-beta 1,4-galactosyltransferase (beta 1,4-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 Gal-NAc 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.
我们现在报告，α-乳白蛋白（α-LA）对牛乳UDP-半乳糖：N-乙酰葡糖胺-β1,4-半乳糖基转移酶（β1,4-GT）具有一种新的作用，并诱导该酶有效地利用UDP-N-乙酰半乳糖胺作为供体。在α-LA存在的情况下，该酶将N-乙酰半乳糖胺转移至游离的N-乙酰葡糖胺上，以产生N-乙酰半乳糖胺-β1-4N-乙酰葡糖胺，其速率为在不存在α-LA时以UDP-半乳糖作为供体时速率的55%。α-LA的刺激作用取决于α-LA、受体和糖核苷酸的浓度。有趣的是，无论有无α-LA，β1,4-GT都无法将N-乙酰半乳糖胺转移至葡萄糖上。α-LA还刺激了N-乙酰半乳糖胺从UDP-N-乙酰半乳糖胺转移至各种几丁质寡聚物上，尽管随着受体尺寸的增加，刺激程度会降低。因此，牛乳β1,4-GT具有利用两种不同糖核苷酸的内在能力，且糖核苷酸偏好可由α-LA调节。
