On the Biosynthesis of 5‐Methoxybenzimidazole: Precursor‐Function of 5‐Hydroxybenzimidazole, Benzimidazole and Riboflavin

Abstract

In Clostridium thermoaceticum 5‐hydroxybenzimidazole is methylated to 5‐methoxybenz‐imidazole and transformed to 5‐methoxybenzimidazolylcobamide. 5‐Hydroxybenzimidazolylcobamide is also methylated to 5‐methoxybenzimidazolylcobamide. These results indicate a possible precursor function of 5‐hydroxybenzimidazole in the biosynthesis of 5‐methoxybenzimidazole. The same microorganism uses benzimidazole to form benzimidazolylcobamide. This or externally added benzimidazolylcobamide, although taken up by the cells, is not further transformed (i.e. hydroxylated and methylated to 5‐methoxybenzimidazolylcobamide). This excludes a precursor function of benzimidazole in the biosynthesis of 5‐methoxybenzimidazole. Contrary to the biosynthesis of 5,6‐dimethylbenzimidazole, 5‐methoxybenzimidazole is not formed from riboflavin, but riboflavin inhibits the growth and the production of 5‐methoxybenz‐imidazolylcobamide in Clostridium thermoaceticum. A tentative scheme for the biosynthesis of 5‐methoxybenzimidazole via a riboflavin analog is discussed. Copyright © 1975, Wiley Blackwell. All rights reserved