Phenotypic analysis of the ccp1Delta and ccp1Delta-ccp1W191F mutant strains of Saccharomyces cerevisiae indicates that cytochrome c peroxidase functions in oxidative-stress signaling.

Yeast cytochrome c peroxidase (CCP) efficiently catalyzes the reduction of H(2)O(2) to H(2)O by ferrocytochrome c in vitro. The physiological function of CCP, a heme peroxidase that is targeted to the mitochondrial intermembrane space of Saccharomyces cerevisiae, is not known. CCP1-null-mutant cells in the W303-1B genetic background (ccp1Delta) grew as well as wild-type cells with glucose, ethanol, glycerol or lactate as carbon sources but with a shorter initial doubling time. Monitoring growth over 10 days demonstrated that CCP1 does not enhance mitochondrial function in unstressed cells. No role for CCP1 was apparent in cells exposed to heat stress under aerobic or anaerobic conditions. However, the detoxification function of CCP protected respiring mitochondria when cells were challenged with H(2)O(2). Transformation of ccp1Delta with ccp1(W191F), which encodes the CCP(W191F) mutant enzyme lacking CCP activity, significantly increased the sensitivity to H(2)O(2) of exponential-phase fermenting cells. In contrast, stationary-phase (7-day) ccp1Delta-ccp1(W191F) exhibited wild-type tolerance to H(2)O(2), which exceeded that of ccp1Delta. Challenge with H(2)O(2) caused increased CCP, superoxide dismutase and catalase antioxidant enzyme activities (but not glutathione reductase activity) in exponentially growing cells and decreased antioxidant activities in stationary-phase cells. Although unstressed stationary-phase ccp1Delta exhibited the highest catalase and glutathione reductase activities, a greater loss of these antioxidant activities was observed on H(2)O(2) exposure in ccp1Delta than in ccp1Delta-ccp1(W191F) and wild-type cells. The phenotypic differences reported here between the ccp1Delta and ccp1Delta-ccp1(W191F) strains lacking CCP activity provide strong evidence that CCP has separate antioxidant and signaling functions in yeast.