Excision of aflatoxin B₁-imidazole ring opened guanine adducts from DNA by formamidopyrimidine-DNA glycosylase

This investigation has confirmed the earlier reports that when aflatoxin B1-DNA adducts are stored under physiological conditions some aflatoxin B1-guanine adducts are converted to a secondary product in which fission of the imidazole ring of the adduct guanine has occurred. Incubation of DNA containing aflatoxin B1-guanine adducts for an increasing number of hours under physiological conditions resulted in a progressive increase in the number of adducts in which the imidazole rings of guanines underwent fission. It was shown that the Escherichia coli enzyme, formamidopyrimidine-DNA glycosylase exercises from the 6-day incubated DNA, an amount of imidazole ring opened guanines equivalent to 40% of the aflatoxin B1-guanine adducts present in the DNA. The enzymatic excision of imidazole ring opened aflatoxin B1-guanine adducts is inhibited by Cibacron Blue F3GA a strong inhibitor of formamidopyrimidine-DNA glycosylase. Treatment of aflatoxin B1-DNA with mild alkali (pH 9.6), resulted in a 2-fold increase in the amount of aflatoxin B1-guanines with opened imidazole rings; this was revealed by enzyme assays using this alkaline treated DNA substrate as well as by analysis of acid hydrolysates of the alkaline treated DNA.