Fluorometric study of DNA-bound benzo[a]pyrene

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Abstract
Comparisons were made among the fluorescence spectra of DNA-bound benzo[a]pyrenes which were produced in vivo and in vitro. DNA from mouse skin treated with benzo[a]pyrene had a maximum emission beyond 400 nm, which was clearly distinguished from that of DNA-bound benzo[a]pyrene 4,5-oxide. The emission spectra from mouse skin were classified into two groups, type I and type II. The former was similar to the spectrum of benzo[a]pyrene, although the two maxima were shifted to longer wavelengths (410 and 435 nm). Type II was characterized by a broad peak around 430 nm. Type I and type II were obtained from different fractions of hydroxylapatite chromatography, but type I was changed into type II during storage. This suggests that type II is a modified product of type I. The emission spectra of both groups also were detected in in vitro activating systems, including photoirradiation, iodine treatment, and hydrogen peroxide treatment. Treatment of Escherichia coli with benzo[a]pyrene during culture produced only fluorescence of type I. Although the relationship between types I and II remains to be established, both types of fluorescence evidently indicate that the conjugated ring structure of the parent compound, benzo[a]pyrene, is preserved intact in DNA-bound benzo[a]pyrene. Several lines of evidence suggest that the proximate (active) form is an unidentified hydroxylated product including an oxy radical, but a cation radical cannot be completely excluded.

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