Tumor cells have an absence or deficiency of mitochondrial superoxide dismutase. Superoxide is produced when hematoporphyrin derivative is exposed to visible light. A significant portion of the antitumor effect of porphyrin: light therapy is hypothesized to be mediated by superoxide.
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We are most appreciative of the helpful comments of Dr. S. Schwartz. Drs. J.M. Gerrard, J.G. White, and G.H.R. Rao are also acknowledged. We also wish to thank Linda Richter, Jan De Lue, and Mary Jo Showalter for technical assistance. This work was partially supported by USPHS Grant AM12466 to S. Schwartz. Dr. Peterson is an established investigator of the West Duluth Research Foundation.