PHOTO-INDUCED BINDING OF SULFANILAMIDE TO CELLULAR MACROMOLECULES

Abstract— Ultraviolet light (A > 295 nm) induced binding of sulfanilamide to cellular macromoleculcs has been examined. It was found that the drug bound irreversibly to native DNA, and complexes containing one drug molecule per 80 nucleotides were obtained after 60 min of irradiation under anaerobic conditions. Oxygen reduced this binding significantly. More drug was bound to RNA and heat denatured DNA under identical conditions. The binding of sulfanilamide to DNA was found to induce nicking of circular closed plasmid DNA and cross-linking of calf thymus DNA. Oxygen significantly decreased nicking and cross-linking of DNA. Irradiation of sulfanilamide and human serum albumin resulted in covalent binding of the drug to the protein and a concomitant increase in protein crosslink-ing. While oxygen decreased covalent binding, crosslinking increased under aerobic conditions. These reactions may be important in the photosensitization caused by sulfanilamide.