The biosynthesis of pteridines. Part VI. Studies of the mechanism of riboflavin biosynthesis

Abstract

¹ H N.m.r. spectroscopy has been used to study the deuterium exchange of the methyl protons in the lumazine precursor (6,7-dimethyl-8-D-ribitylpteridine-2,4-dione) of riboflavin, and in related compounds. The protons of the 7-methyl group exchange with the solvent, whereas those of the 6-methyl group do not. An explanation which involves a highly delocalized anionic species is suggested.

One of the labelled lumazines has been converted into the corresponding flavin by an in vitro reaction which closely simulates the biosynthesis of riboflavin. The distribution of deuterium label in the flavin has been established, and a mechanism for its formation is proposed. The relevance of the results to the mechanism of the enzymic synthesis of riboflavin is discussed.