Alworth W L, Dove M F, Baker H N
Biochemistry. 1977 Feb 8;16(3):526-31. doi: 10.1021/bi00622a029.
The relative incorporations of specially labeled pyruvate, lactate, erythritol, D-erythrose, D-ribose, and D-glucose precursors into the dimethylbenzene carbon atoms of the 5,6-dimethylbenzimidazole unit of vitamin B12 by Propionibacterium shermanii have been determined. The incorporation data provide information regarding the putative four-carbon biosynthetic unit which is involved in the formation of 6,7-dimethyl-8-ribityllumazine and which is the source of the eight dimethylbenzene carbon atoms of both 5,6-dimethylbenzimidazole and riboflavin. The relative incorporations of the labeled lactate and pyruvate precursors are not consistent with either acetoin or 2,3-butanedione functioning as the four-carbon biosynthetic unit. The relative incorporations of the labeled hexose, pentose, and tetrose precursors indicate that the observed incorporation of C-1 of the pentose into the dimethylbenzene carbon atoms does not involve metabolism to a tetrose intermediate, but occurs more directly. It is concluded that the C-1 position of a pentose precursor is involved in the formation of the putative four-carbon biosynthetic unit.
已测定了特别标记的丙酮酸、乳酸、赤藓糖醇、D-赤藓糖、D-核糖和D-葡萄糖前体被谢氏丙酸杆菌掺入维生素B12的5,6-二甲基苯并咪唑单元的二甲基苯碳原子中的相对掺入量。这些掺入数据提供了有关假定的四碳生物合成单元的信息，该单元参与6,7-二甲基-8-核糖基-lumazine的形成，并且是5,6-二甲基苯并咪唑和核黄素的八个二甲基苯碳原子的来源。标记的乳酸和丙酮酸前体的相对掺入量与乙偶姻或2,3-丁二酮作为四碳生物合成单元的功能均不一致。标记的己糖、戊糖和丁糖前体的相对掺入量表明，观察到的戊糖的C-1掺入二甲基苯碳原子中并不涉及代谢为丁糖中间体，而是更直接地发生。得出的结论是，戊糖前体的C-1位置参与了假定的四碳生物合成单元的形成。
