Prolonged exposure to
hyperoxia represents a serious danger to cells, yet little is known about the specific cellular factors that affect
hyperoxia stress. By screening the yeast deletion library, we have identified genes that protect against high-O2 damage. Out of approx. 4800 mutants, 84 were identified as
hyperoxia-sensitive, representing genes with diverse cellular functions, including transcription and translation, vacuole function,
NADPH production, and
superoxide detoxification.
Superoxide plays a significant role, since the majority of
hyperoxia-sensitive mutants displayed cross-sensitivity to
superoxide-generating agents, and mutants with compromised SOD (
superoxide dismutase) activity were particularly vulnerable to
hyperoxia. By comparison, factors known to guard against H2O2 toxicity were poorly represented amongst
hyperoxia-sensitive mutants. Although many cellular components are potential targets, our studies indicate that mitochondrial
glutathione is particularly vulnerable to
hyperoxia damage. During
hyperoxia stress, mitochondrial
glutathione is more susceptible to oxidation than cytosolic
glutathione. Furthermore, two factors that help maintain mitochondrial GSH in the reduced form, namely the
NADH kinase Pos5p and the mitochondrial
glutathione reductase (Glr1p), are critical for
hyperoxia resistance, whereas their cytosolic counterparts are not. Our findings are consistent with a model in which
hyperoxia toxicity is manifested by
superoxide-related damage and changes in the mitochondrial redox state.