Abstract
Platinum-pyrimidine complexes have been used as the sole electron-dense stains for electron microscopy on 18 types of mammalian cells. These recently discovered complexes react avidly with nucleic acids in vitro, are antitumor agents, and are highly soluble in water. In cells, they are selective for regions rich in nucleic acid and make visible the cellular chromatin, nucleolus, and ribosomes. In addition, cells that are tumorigenic exhibit electron-dense patches at the plasma membrane; normal cells do not. The results of treatment of ascites sarcoma-180 cells with concanavalin A, nucleases, glycosidases, or a protease suggest that the electron-dense patches are DNA, with neuroaminic acid involved in the surface binding.