Effects of ultraviolet radiation on 3,4-benzpyrene and other polycyclic aromatic hydrocarbons; carcinogenic activity of aqueous extracts from irradiated 3,4-benzpyrene.

It was shown in preceding papers (2, 3) that when 3,4-benzpyrene dissolved in benzene was irradiated with monochromatic radiation of wave length 2,537 A. in the presence of oxygen, at least two water-soluble substances were included in the products and that these could be recognized, and some of their properties deduced, by spectrophotometric methods. The first, substance A, was characterized at pH 8 by an absorption band whose maximum intensity was at 3,600 A. It was labile, readily taking up atmospheric oxygen irreversibly when its aqueous solutions were allowed to stand at room temperature; but it could be stabilized by cooling them to 0 ~ C. and storing them in an atmosphere of nitrogen. The second substance, B, absorbed at 2,760 A. and was more stable to oxygen, but it was destroyed by strong alkali. It reacted readily with glutathione and with other compounds containing sulfhydryl groups. Water-soluble oxidation products of 3,4-benzpyrene are of course well known. A monohydroxy derivative is excreted as a metabolite when the hydrocarbon is fed to rats (8, 13); and a photoderivative has been described that has the power to inhibit respiratory enzymes (6, 7). None of them, however, has been reported to have any carcinogenic activity. Rideal and Schulman have shown (12) that materials very similar to, if not identical with, substances ,4 and B are readily adsorbed onto protein monolayers, and so might be expected to pass more readily than the unadsorbed hydrocarbon through cell membranes. By analogy with hemolytic substances, which they showed to possess this property to a high degree, substances ,4 and B might thus be expected to be biologically active. Other observations recorded in the literature, which were summarized in the introduction to Part I, seem to support this view. Since the absorption bands of ,4 and B do not accord with those of any derivative