Tyrosine 70 fine-tunes the catalytic efficiency of aspartate aminotransferase.
Tyrosine 70 fine-tunes the catalytic efficiency of aspartate aminotransferase.
复制标题
酪氨酸 70 微调天冬氨酸转氨酶的催化效率。
DOI：
10.1021/bi00244a013
复制
发表时间：
1991
期刊：
影响因子：
2.9
通讯作者：
Kirsch,JF
中科院分区：
文献类型：
--
作者：
Toney,MD;Kirsch,JF
天门冬氨酸转氨酶突变体Y70F在天门冬氨酸和酮戊二酸转氨酶方面表现出kat= 8%和kat/KM= 2%的野生型值。突变后，该酶对非共价结合抑制剂马来酸盐的亲和力降低了17倍，而对形成稳定的共价外醛胺的甲基天冬氨酸的亲和力仅降低了2.5倍。野生型与j8-羟基天冬氨酸反应形成的喹诺酮中间体高群体因突变而减少75%以上。Y70F C”-H对天冬氨酸反应的动力学同位素效应值大于野生型（DF= 2.4 vs 1.52; D (V/K)= 2.5 vs 1.7）。相反，谷氨酸反应的Y70F值（V/K）与野生型相比降低（1.75 vs 2.5）。这些结果，结合之前对Lys258突变体的研究，消除了Tyr70作为催化装置的重要组成部分，但需要注意的是，被删除的羟基的功能可能被水分子所取代。
The aspartate aminotransferase mutant Y70F exhibits kat= 8% and kat/KM= 2% of the wild type values for the transamination of aspartate and-ketoglutarate. The affinity of the enzyme for the noncovalently bound inhibitor maleate is reduced 17-fold by the mutation, while only a 2.5-fold reduction is observed for-methylaspartate, which forms a stable, covalent external aldimine. The high population of the quinonoid intermediate formed in the reaction of the wild type with j8-hydroxyaspartate is more than 75% diminished by the mutation. Thevalues of the Y70F C “-H kinetic isotope effects for the aspartate reaction are larger than those of wild type (DF= 2.4 vs 1.52; D (V/K)= 2.5 vs 1.7). Conversely, the Y70F value of (V/K) for the glutamate reaction is decreased compared to wild type (1.75 vs 2.5). These results, combined with previous studies of Lys258 mutants, eliminate Tyr70 as an essential component of the catalytic apparatus, with thecaveat that the functionality of the deleted hydroxyl group is possibly replaced by a water molecule.