Two mechanisms of near-ultraviolet lethality in Saccharomyces cerevisiae: A respiratory capacity-dependent and an irreversible inactivation

Near-ultraviolet irradiation of actively growing yeast cells leads to cell death by two distinct mechanisms. The first type of cell death is evident after low doses of near-ultraviolet light (3 · 10⁴ ergs · mm⁻²) and is due to a areversible inactivation of the respiratory capacity of the cell. In studies with yeast mitochondrial membranes the quinones were identified as the site of inactivation by determining the relative levels of the following oxidase activities after irradiation: exogenous NADH, endogenous NADH (via isocitrate dehydrogenase), succinate, and D-lactate oxidases. A second type of cell death is caused after high doses (1.8 · 10⁵ ergs · mm⁻²) and is irreversible. The mechanism of this inactivation is unknown.