Physiological Characteristics of <i>Saccharomyces cerevisiae</i> Strain Overexpressing Polyphosphatase Ppx1

Abstract

Abstract—The Ррх1 exopolyphosphatase of yeast is a constitutive protein localized predominantly in the cytoplasm. The purified enzyme hydrolyzes inorganic polyphosphates with high activity; however, in the knockout ∆ppx1 mutant of Saccharomyces cerevisiae the increase in the polyphosphate level was small, and no changes in physiological properties of this mutant were observed. To elucidate the functions of Ppx1, we studied the physiological characteristics of the S. cerevisiae strain overexpressing this enzyme. When cultivated in the YPD medium, the strain overexpressing Ppx1 showed no growth features different from those of the parental strain. The following physiological features of the strain overexpressing Ppx1 were observed at the stationary stage of growth: the level of ATP increased by nine times, the activity of vacuolar ATPase significantly decreased, and the sensitivity to peroxide increased compared to the parental strain. The level of reactive oxygen species doubled, while the degree of lipid oxidation remained the same as in parental strain. Since overexpression of Ppx1 under the culture conditions used did not affect the polyphosphate level, these polymers were not the regulators of the changes described above. Response to oxidative stress and vacuolar ATPase activity in yeasts is known to be regulated by cAMP, while Ppx1 is capable of hydrolyzing this signaling compound. We suggest that one of the functions of Ppx1 in yeasts is participation in the regulation of cAMP level.