Enhancing Effect of Ascorbate on Toluidine Blue‐photosensitization of Yeast Cells

Using toluidine blue, a potent photosensitizer with a 1 O 2 dominated mechanism in yeast cell inactivation, it was found that addition of ascorbate to the sensitizer‐cell mixture during illumination enhanced the inactivation. The enhancement required the presence of oxygen in the reaction mixture. The same enhancement was observed with methylene blue and thionine but not with xanthenes (Rose Bengal and eosin Y). The consumption of O 2 and ascorbate seemed coupled in the enhancement. From the observation that the presence of ascorbate for a very short time (1 s) in the reaction mixture was enough to exhibit the same enhancement, it was concluded that the ascorbate enhancement processes are probably initiated in bulk medium, not intracellularly. The ascorbate enhancement may be a combined consequence of the high electron‐accepting property of triplet toluidine blue and the strong tendency of ascorbate to act as an electron donor. The role of oxygen was not specified whether it was directly involved in the photoinactivation of cells. Addition of N J appeared to suppress the photoinacti‐vation only in the higher fluence region where ascorbate had been consumed. Thus the ascorbate enhancement seems to occur under low fluence conditions and may probably be independent of the singlet oxygen mechanism.