Abstract

The role of cytochrome c peroxidase (CCP), found in yeasts and some bacteria, is not clear. However, it is believed to play a role in H 2 O 2 detoxification. To probe the physiological role of CCP, a yeast strain deficient in the gene encoding CCP (x ccp1 ) was engineered and characterized with respect to growth on various carbon sources, respiratory competence, resistance to H 2 O 2 , activities of various antioxidant enzymes, and levels of glutathione. Mitochondria of x ccp1 yeast were found to undergo time-dependent inactivation and the x ccp1 strain was found to be more susceptible to H 2 O 2 induced stress, as compared to the isogenic wild-type strain, during both its exponential and stationary phases of growth. Despite this increased sensitivity to H 2 O 2 , x ccp1 was still able to adapt to stress. Furthermore, antioxidant enzymes such as glutathione reductase and catalase as well as the antioxidant glutathione, which are all regulated through the transcription factor YAP1, showed reduced activity in the x ccp1 strain compared to the isogenic wild-type strain, possibly explaining the increased sensitivity of x ccp1 cells to H 2 O 2 . The x ccp1 strain also showed decreased phosphatase and increased kinase activities. These results suggest that CCP is involved in protecting mitochondria from H 2 O 2 generated through normal metabolic reactions; as well as from exogenous H 2 O 2 challenges. They also indicate that CCP and/or H 2 O 2 are involved in signal transduction in yeast. The creation of a yeast strain deficient in thioredoxin peroxidase (x tsa1 ), and its possible involvement in redox signaling, is also discussed.