Growth inhibition dependent on reactive oxygen species generated by C9-UK-2A, a derivative of the antifungal antibiotic UK-2A, in Saccharomyces cerevisiae.

UK-2A is a potent antifungal antibiotic and its structure is highly similar to that of antimycin A3 (AA). UK-2A and AA inhibit mitochondrial electron transport at complex III. C9-UK-2A, which has been prepared to improve the duration of the antifungal activity of UK-2A, shows durable fungicidal activities against various species of fungi and induces both membrane injury and the generation of cellular reactive oxygen species (ROS) against Rhodotorula mucilaginosa IFO 0001 cells. We found that C9-UK-2A inhibited the vegetative growth of Saccharomyces cerevisiae IFO 0203 cells accompanying cellular ROS generation in Sabouraud dextrose (SD) medium, which contained a fermentable carbon source. The ROS generation was completely restricted by pretreatment with a lipophilic antioxidant alpha-tocopherol. In addition, the pretreatment with the antioxidant protected against the growth inhibition induced by C9-UK-2A. C9-UK-2A also induced ROS generation in isolated mitochondria of the S. cerevisiae cells. The addition of both a complex I inhibitor rotenone and a complex II inhibitor thenoyltrifluoroacetone reduced ROS generation induced by C9-UK-2A in the whole cells and the isolated mitochondria. The addition of the inhibitors of complex III, AA or myxothiazol, or of complex IV, KCN, did not reduce ROS generation. These results suggest that C9-UK-2A induces ROS generation due to the blockade of electron flow at complex III, thereby inhibiting the growth of S. cerevisiae in SD medium.