Lowary T L, Hindsgaul O
Department of Chemistry, University of Alberta, Edmonton, Canada.
Carbohydr Res. 1994 Jan 3;251:33-67. doi: 10.1016/0008-6215(94)84275-2.
The disaccharide alpha-L-Fuc p-(1-->2)-beta-D-Gal p-O-(CH2)7CH3 (6) is an acceptor for the glycosyltransferases responsible for the biosynthesis of the A and B blood-group antigens. These enzymes respectively transfer GalNAc and Gal in an alpha linkage to OH-3 of the Gal residue in 6. All eight possible O-methyl, epimeric, and amino analogues of 6 having modifications on the target Gal residue were chemically synthesized and kinetically evaluated both as substrates and inhibitors for the A and B glycosyltransferases. The results support earlier findings that both enzymes will tolerate replacement of the hydroxyl groups at the 3 and 6 positions of the Gal residue. Substitution at or replacement of OH-4 of the Gal residue, however abolishes recognition. The 6-O-methyl and 6-amino compounds are substrates for both enzymes while the 3-epimeric (10) and 3-amino (12) compounds are inhibitors. For the B transferase, 10 is a competitive inhibitor with a Ki of 7.8 microM. Attempts to determine a Ki for 12 with the B transferase were unsuccessful because of a complex mode of inhibition. Similarly, both 10 and 12 are potent inhibitors of the A transferase, but the inhibition constants could not be calculated because of a complex mode of inhibition, resembling that for the B transferase. With the A transferase, 12 had an estimated Ki in the 200 nM range.
二糖α-L-岩藻糖基-(1→2)-β-D-半乳糖基-O-(CH₂)₇CH₃(6)是负责A和B血型抗原生物合成的糖基转移酶的受体。这些酶分别以α键将N-乙酰半乳糖胺和半乳糖转移至6中半乳糖残基的OH-3位。对6中目标半乳糖残基进行修饰的所有8种可能的O-甲基、差向异构和氨基类似物均被化学合成，并作为A和B糖基转移酶的底物和抑制剂进行了动力学评估。结果支持了早期的发现，即这两种酶都能耐受半乳糖残基3位和6位羟基的取代。然而，半乳糖残基OH-4位的取代或替换会消除识别。6-O-甲基和6-氨基化合物是这两种酶的底物，而3-差向异构体(10)和3-氨基(12)化合物是抑制剂。对于B转移酶，10是一种竞争性抑制剂，Ki为7.8 microM。由于抑制模式复杂，未能成功测定12对B转移酶的Ki。同样，10和12都是A转移酶的有效抑制剂，但由于抑制模式复杂，类似于B转移酶，无法计算抑制常数。对于A转移酶，12的估计Ki在200 nM范围内。
