Requirement for reducing agents in deoxyribonucleic acid strand scisson by the purified chromophore of auromomycin.

By methanol extraction and high-pressure liquid chromatography a nonprotein chromophore has been obtained from the antitumor protein antibiotic auromomycin (AUR) which possesses the cytotoxic and the in vivo and in vitro deoxyribonucleic acid (DNA) strand scission activities of the parent material. The rate of DNA strand breakage by the purified chromophore is markedly stimulated by reducing compounds (maximally at approximately 0.1 mM dithiothreitol), but DNA strand scission activity is lost upon pretreatment of the chromophore with these agents. Apoprotein specifically protects against such inactivation but blocks the activity of both the stimulated and unstimulated reactions, presumably by complexing the chromophore and making it less available to the target DNA. Dithiothreitol-dependent scission of DNA by chromophore is faster and more complete at 0 degrees C than at 37 degrees C. The reaction at 0 degrees C is almost entirely dependent on the presence of a reducing compound. Although 2-mercapto-ethanol does not stimulate the reaction of either AUR or its chromophore at 37 degrees C, it has a significant stimulatory effect at 0 degrees C.