Biosynthesis of Riboflavin. Single Turnover Kinetic Analysis of 6,7-Dimethyl-8-ribityllumazine Synthase
作者:Nicholas Schramek、Ilka Haase、Markus Fischer、Adelbert Bacher
DOI:10.1021/ja028226k
日期:2003.4.1
6,7-dimethyl-8-ribityllumazine synthase (lumazine synthase) catalyzes the condensation of 5-amino-6-ribitylamino-2,4-(1H,3H)-pyrimidinedione with 3,4-dihydroxy-2-butanone 4-phosphate, affording the riboflavin precursor, 6,7-dimethyl-8-ribityllumazine. Single turnover experiments monitored by multiwavelength photometry were performed with the recombinant lumazine synthase of Bacillus subtilis. Mixing
6,7-二甲基-8-核嘧啶合酶(lumazine synthase)催化 5-amino-6-ribitylamino-2,4-(1H,3H)-pyrimidinedione 与 3,4-dihydroxy-2-butanone 4-phosphate 的缩合,提供核黄素前体 6,7-二甲基-8-核黄素。通过多波长光度法监测的单周转实验是用枯草芽孢杆菌的重组 lumazine 合酶进行的。酶与嘧啶类底物的混合有利于低色移以及杂环底物吸光度的降低;该反应的速率常数为 0.02 s(-1) microM(-1)。酶和嘧啶型底物之间的复合物与第二种底物 3,4-二羟基-2-丁酮 4-磷酸快速混合,随后出现早期光学瞬态,其特征是在 330 nm 处的低强度吸收最大值,暂时将其指定为席夫碱中间体。随后磷酸盐的消除提供了在 455 和 282 nm 处具有强烈吸收最大值的瞬态,表明中间体具有扩展的共轭双键系统。随后形成的酶产物