The intermediate in the degradation of DNA alkylated with a monofunctional alkylating agent

Abstract

The course of DNA degradation following alkylation with a monofunctional alkylating agent can be accounted for by the scheme: A → k 1 B → k 2 where A represents alkylated DNA, B represents DNA with apurinic sites, and C indicates DNA containing single-strand breaks. Apurinic sites in DNA were estimated as the fraction of the DNA made acid soluble by treatment with alkali. A simple method for comparing the rate of depurination for DNA alkylated with different groups is described. The rate of hydrolysis of apurinic sites depended on the buffer; buffers with primary amino groups such as Tris or glycinamide promoted hydrolysis of apurinic acid at a pH near neutrality. Alkaline phosphatase-sensitive groups were exposed as a result of the degradation of DNA. The proportion of phosphatase-sensitive to acid-soluble groups remained constant throughout the course of the degradation of methylated or ethylated DNA. We conclude that apurinic acids are necessary intermediates in the degradation in vitro of alkylated DNA. Ethylated and methylated DNA's decay by the same reaction mechanism.