SYNERGISTIC INTERACTION BETWEEN THE TRYPTOPHAN PHOTOPRODUCTS AND NEAR-ULTRAVIOLET LIGHT IN AMOEBA

Abstract. Both S- and G₂-phase cells of amoeba are found to be sensitized by coirradiation of cells with Tryptophan (Trp). At a fluence of 1.5 times 10⁵ Jm^-2 to which G₂ phase cells are resistant, they show a drastic (8-fold) increase in sensitivity when irradiated in 0.5% Trp solution. Freshly irradiated Trp solution is found to be lethal to G₂ cells that have received a sublethal fluence of near-UV light. Irradiated Trp, however, does not kill unirradiated amoeba.
Nuclear transplantation experiments have shown that the lethality of cells when coirradiated with Trp is due to damage located predominantly in the cytoplasm. It is suggested that sublethal fluence of near-UV light makes the cells "leaky" to the toxic photooxidation products of Trp solution.