Uchida Akira, Ogawa Mina, Yoshida Toyokazu, Nagasawa Toru
Department of Biomolecular Science, Gifu University, Yanagido 1-1, 501-1193, Gifu, Japan.
Arch Microbiol. 2003 Aug;180(2):81-7. doi: 10.1007/s00203-003-0573-0. Epub 2003 Jul 3.
In the conversion of quinolinic acid to 6-hydroxypicolinic acid by whole cells of Alcaligenes sp. strain UK21, the enzyme reactions involved in the hydroxylation and decarboxylation of quinolinic acid were examined. Quinolinate dehydrogenase, which catalyzes the first step, the hydroxylation of quinolinic acid, was solubilized from a membrane fraction, partially purified, and characterized. The enzyme catalyzed the incorporation of oxygen atoms of H(2)O into the hydroxyl group. The dehydrogenase hydroxylated quinolinic acid and pyrazine-2,3-dicarboxylic acid to form 6-hydroxyquinolinic acid and 5-hydroxypyrazine-2,3-dicarboxylic acid, respectively. Phenazine methosulfate was the preferred electron acceptor for quinolinate dehydrogenase. 6-Hydroxyquinolinate decarboxylase, catalyzing the nonoxidative decarboxylation of 6-hydroxyquinolinic acid, was purified to homogeneity and characterized. The purified enzyme had a molecular mass of approximately 221 kDa and consisted of six identical subunits. The decarboxylase specifically catalyzed the decarboxylation of 6-hydroxyquinolinic acid to 6-hydroxypicolinic acid, without any co-factors. The N-terminal amino acid sequence was homologous with those of bacterial 4,5-dihydroxyphthalate decarboxylases.
在产碱菌属UK21菌株的全细胞将喹啉酸转化为6-羟基吡啶甲酸的过程中，对喹啉酸羟基化和脱羧过程中涉及的酶反应进行了研究。催化第一步反应即喹啉酸羟基化的喹啉酸脱氢酶从膜组分中溶解出来，进行了部分纯化并对其特性进行了表征。该酶催化将H₂O中的氧原子掺入到羟基中。该脱氢酶将喹啉酸和吡嗪-2,3-二羧酸羟基化，分别形成6-羟基喹啉酸和5-羟基吡嗪-2,3-二羧酸。硫酸吩嗪甲酯是喹啉酸脱氢酶的首选电子受体。催化6-羟基喹啉酸非氧化脱羧反应的6-羟基喹啉酸脱羧酶被纯化至同质并对其特性进行了表征。纯化后的酶分子量约为221 kDa，由六个相同的亚基组成。该脱羧酶特异性地催化6-羟基喹啉酸脱羧生成6-羟基吡啶甲酸，无需任何辅助因子。其N端氨基酸序列与细菌4,5-二羟基邻苯二甲酸脱羧酶的序列同源。
