Stoichiometry of DNA strand scission and aldehyde formation by bleomycin.

A colorimetric assay of DNA breakage by bleomycin has been standardized and indicates that strand scission is stoichiometric with the formation of a single equivalent of an aldehyde compound consisting of base plus deoxyribose carbons 1' to 3'. Both strand scission and aldehyde formation require the presence of O2. An alternate DNA lesion inflicted by bleomycin, alkali labilization, is O2-dependent, as is the accompanying release of free bases.