Effect of Some Benzimidazoles on a Vitamin B₁₂-requiring Alga

Abstract

THE identification of 5 : 6-dimethyl benzimidazole (I) as an acid degradation product of vitamin B₁₂ was made in 1949 by Brink and Folkers¹ and independently by Holiday and Petrow². The latter authors also speculated on the biogenesis of vitamin B₁₂ and riboflavin, and suggested the possibility of their common derivation from 4 : 5-dimethyl-o-phenylenediamine (II)—a chemical precursor of (I). Furthermore, both these compounds were shown by Emerson et al. ³ to possess vitamin B₁₂-like activity in the rat. McNair Scott, Rogers and Rose⁴ tested 49 substituted benzimidazoles on several bacterial systems—including the vitamin B₁₂-requiring E. coli 113-3. In particular, they found that—SH and — NO₂ substitution in the 4-position was associated with competitive vitamin B₁₂ antagonism. More recently, Timmis and Epstein⁵ demonstrated that 4,5,6-trichloro benzimidazole and its corresponding 1-β-D-ribofuranosyl were non-competitive and competitive antagonists respectively in the highly sensitive vitamin B₁₂-dependent flagellated green alga Euglena gracilis var. z.