Dihydropyrimidine amidohydrolases and dihydroorotases share the same origin and several enzymatic properties
作者:Z. Gojkovic
DOI:10.1093/nar/gkg258
日期:2003.3.15
Slime mold, plant and insect dihydropyrimidine amidohydrolases (DHPases, EC 3.5.2.2), which catalyze the second step of pyrimidine and several anti‐cancer drug degradations, were cloned and shown to functionally replace a defective DHPase enzyme in the yeast Saccharomyces kluyveri . The yeast and slime mold DHPases were over‐expressed, shown to contain two zinc ions, characterized for their properties and compared to those of the calf liver enzyme. In general, the kinetic parameters varied widely among the enzymes, the mammalian DHPase having the highest catalytic efficiency. The ring opening was catalyzed most efficiently at pH 8.0 and competitively inhibited by the reaction product, N ‐carbamyl‐β‐alanine. At lower pH values DHPases catalyzed the reverse reaction, the closing of the ring. Apparently, eukaryote DHPases are enzymatically as well as phylogenetically related to the de novo biosynthetic dihydroorotase (DHOase) enzymes. Modeling studies showed that the position of the catalytically critical amino acid residues of bacterial DHOases and eukaryote DHPases overlap. Therefore, only a few modifications might have been necessary during evolution to convert the unspecialized enzyme into anabolic and catabolic ones.
粘菌、植物和昆虫二氢嘧啶酰胺水解酶(DHPases,EC 3.5.2.2)可催化嘧啶的第二个步骤以及多种抗癌药物的降解,研究人员对这种酶进行了克隆,并证明其能够替代克鲁维酵母(Saccharomyces kluyveri)中缺陷的DHPase酶。研究人员对酵母和粘菌的DHPases进行了过量表达,发现它们含有两个锌离子,并对其性质进行了描述,并与小牛肝酶进行了比较。一般来说,不同酶的动力学参数差异很大,哺乳动物的DHPase具有最高的催化效率。在pH值为8.0时,环开环反应的催化效率最高,而反应产物N-氨基甲酰-β-丙氨酸会竞争性抑制该反应。在较低的pH值下,DHPases会催化相反的反应,即环的闭合。显然,真核生物的DHPases在酶学和系统发育上与从头生物合成二氢乳清酸酶(DHOase)酶有关。建模研究表明,细菌DHOases和真核生物DHPases中催化关键氨基酸残基的位置重叠。因此,在进化过程中,可能只需要进行一些修改,即可将非特异性酶转化为合成代谢酶和分解代谢酶。