Wong Y H, Winer F B, Frey P A
Biochemistry. 1979 Nov 27;18(24):5332-6. doi: 10.1021/bi00591a011.
The synthesis of p-(bromoacetamido)phenyl uridyl pyrophosphate (BUP) is described. This compound is an active-site-directed irreversible inhibitor of Escherichia coli UDP-galactose 4-epimerase. The inactivation follows pseudo-first-order kinetics at pH 8.5 in nonnucleophilic buffers, and a saturation effect is seen in the pseudo-first-order rate constant as the concentration of BUP is increased. The half-saturation parameter for BUP in the inactivation is 0.21 +/- 0.02 mM, which compares favorably with the inhibition constant of 0.3 +/- 0.05 mM for BUP acting as a competitive reversible inhibitor of the enzyme. The inactivation rate is slow, however, with a minimum half-time of 12 h at pH 8.5 and 27 degrees C. Both specific alkylation and nonspecific alkylation by BUP occur, but nonspecific alkylation is faster than the inactivation and the rate of inactivation correlates well with the rate of covalent incorporation of one molecule of [14C]BUP at the active site.
描述了对-（溴乙酰氨基）苯基尿苷二磷酸（BUP）的合成。该化合物是大肠杆菌UDP-半乳糖4-差向异构酶的活性位点导向不可逆抑制剂。在pH 8.5的非亲核缓冲液中，失活遵循准一级动力学，随着BUP浓度的增加，准一级速率常数出现饱和效应。BUP失活的半饱和参数为0.21±0.02 mM，与BUP作为该酶竞争性可逆抑制剂时的抑制常数0.3±0.05 mM相比更有利。然而，失活速率较慢，在pH 8.5和27℃下最小半衰期为12小时。BUP会发生特异性烷基化和非特异性烷基化，但非特异性烷基化比失活更快，且失活速率与一分子[14C]BUP在活性位点的共价掺入速率密切相关。
