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

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Abstract
This investigation has confirmed the earlier reports that when aflatoxin [AF] B1-DNA adducts are stored under physiological conditions some AFB1-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 AFB1-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. 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 AFB1-guanine adducts present in the DNA. The enzymatic excision of imidazole ring opened AFB/1-guanine adducts is inhibited by Cibacron Blue F3GA a strong inhibitor of formamidopyrimidine-DNA glycosylase. Treatment of AFB1-DNA with mild alkali (pH 9.6), resulted in a 2-fold increase in the amount of AFB1-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. [AFB1 is a carcinogen.].

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