Renz P, Endres B, Kurz B, Marquart J
Institut für Biologische Chemie und Ernährungswissenschaft, Universität Hohenheim, Stuttgart, Germany.
Eur J Biochem. 1993 Nov 1;217(3):1117-21. doi: 10.1111/j.1432-1033.1993.tb18344.x.
Eubacterium limosum transformed [2-13C]5-hydroxybenzimidazole not only into [2-13C]5-hydroxybenzimidazolylcobamide, but also into [2-13C]5-methoxy-6-methylbenzimidazolylcobamide and into [2-13C]5,6-dimethylbenzimidazolylcobamide (vitamin B12). [2-13C]5-Hydroxy-6-methyl-benzimidazole was used by this bacterium to form [2-13C]5-hydroxy-6-methylbenzimidazolyl-cobamide, [2-13C]5-methoxy-6-methylbenzimidazolylcobamide and [2-13C]5,6-dimethylbenzimidazolylcobamide. The 1H-NMR spectrum of the 5,6-dimethylbenzimidazole isolated from the 13C-labeled vitamin B12 preparations revealed that the externally added bases had been transformed into the vitamin B12 base almost without dilution of the label. This suggests that 5-hydroxybenzimidazole and 5-hydroxy-6-methylbenzimidazole are precursors of 5,6-dimethylbenzimidazole. On the basis of these results, a hypothetical scheme for the biosynthesis of 5,6-dimethylbenzimidazole via 5-hydroxybenzimidazole and 5-hydroxy-6-methylbenzimidazole is discussed. This scheme can also explain the formation of the other benzimidazole bases found in natural vitamin B12 analogs.
黏液真杆菌将[2-¹³C]5-羟基苯并咪唑不仅转化为[2-¹³C]5-羟基苯并咪唑基钴胺素，还转化为[2-¹³C]5-甲氧基-6-甲基苯并咪唑基钴胺素和[2-¹³C]5,6-二甲基苯并咪唑基钴胺素（维生素B12）。该细菌利用[2-¹³C]5-羟基-6-甲基苯并咪唑形成[2-¹³C]5-羟基-6-甲基苯并咪唑基钴胺素、[2-¹³C]5-甲氧基-6-甲基苯并咪唑基钴胺素和[2-¹³C]5,6-二甲基苯并咪唑基钴胺素。从¹³C标记的维生素B12制剂中分离出的5,6-二甲基苯并咪唑的¹H-NMR光谱表明，外部添加的碱基已几乎没有标记稀释地转化为维生素B12碱基。这表明5-羟基苯并咪唑和5-羟基-6-甲基苯并咪唑是5,6-二甲基苯并咪唑的前体。基于这些结果，讨论了通过5-羟基苯并咪唑和5-羟基-6-甲基苯并咪唑生物合成5,6-二甲基苯并咪唑的假设方案。该方案也可以解释天然维生素B12类似物中发现的其他苯并咪唑碱基的形成。
