Berliner L J, Davis M E, Ebner K E, Beyer T A, Bell J E
Mol Cell Biochem. 1984 Apr;62(1):37-42. doi: 10.1007/BF00230075.
A pictorial map of the lactose synthase (galactosyl transferase) acceptor binding site has been formulated from this and published studies on substrate analogs and inhibitors. The basic requirements are a pyranose, thiopyranose or inositol ring structure and equatorial substituents (if any) at C-2, C-3, C-4, and C-5. The aglycone (at C-1) may be either alpha or beta-, but alpha- is somewhat preferred. In the absence of alpha-lactalbumin galactosyl transferase will accept long chain 2-N-acyl substituents on the glucosamine (GlcNH2) structure. An equatorial amino or N-acetyl substituent (e.g. mannosamine, N-acetylmannosamine) is also a suitable acceptor in the absence of alpha-lactalbumin since both N-acetylglucosamine and N-acetylmannosamine have complementary binding loci for the N-acyl moiety. The aglycone moiety must be equatorial (beta-configuration). However, upon alpha-lactalbumin binding the aglycone specificity allows for axial (alpha-configuration) as well as equatorial substituents. Furthermore, the 2-N-acyl substituent binding locus is blocked beyond a 2-N-hexanoyl group. It is suggested that alpha-lactalbumin binds to a hydrophobic site some distance from the C-2 group.
基于此项研究以及已发表的关于底物类似物和抑制剂的研究，绘制了乳糖合酶（半乳糖基转移酶）受体结合位点的示意图。基本要求是具有吡喃糖、硫代吡喃糖或肌醇环结构，且在C-2、C-3、C-4和C-5位有平伏取代基（如果有的话）。糖苷配基（在C-1位）可以是α型或β型，但α型略占优势。在没有α-乳白蛋白的情况下，半乳糖基转移酶会接受葡糖胺（GlcNH2）结构上的长链2-N-酰基取代基。在没有α-乳白蛋白的情况下，平伏氨基或N-乙酰取代基（例如甘露糖胺、N-乙酰甘露糖胺）也是合适的受体，因为N-乙酰葡糖胺和N-乙酰甘露糖胺都有与N-酰基部分互补的结合位点。糖苷配基部分必须是平伏的（β构型）。然而，在α-乳白蛋白结合后，糖苷配基特异性允许轴向（α构型）以及平伏取代基。此外，2-N-酰基取代基的结合位点在2-N-己酰基以上被阻断。有人提出，α-乳白蛋白与距C-2基团有一定距离的疏水位点结合。
