Studies on oxidative stress : activity levels of antioxidant enzymes in copper, zinc superoxide dismutase - deficient yeast cells expressing cloned Escherichia Coli iron superoxide dismutase

Abstract

The Escherichia coli iron superoxide dismutase (FeSOD) gene was expressed, at two different levels (using episomal and centromeric plasmid systems), in Saccharomyces cerevisiae cells deficient in copper, zinc superoxide dismutase. Levels of antioxidant enzymes were studied in the recombinant strains in the presence and absence of 1 mM paraquat in minimal medium. Exposure to paraquat resulted in: (1) increase in the levels of total SOD, FeSOD, and catalase activities in both yeast strains expressing the FeSOD gene, and (2) decrease in the levels of glutathione reductase in yeast cells expressing the cloned FeSOD gene on the episomal, but not on the centromeric, plasmid The increase in FeSOD activity suggested that there is stimulation of the yeast 3-phosphoglycerate kinase gene (PGK) promoter controlling the cloned FeSOD gene in the presence of paraquat This could be either due to the oxidative stress induced by paraquat, or as a result of an inherent effect of paraquat itself. This hypothesis, that is, induction of the PGK promoter in S. cerevisiae under oxidative stress, is presently being studied in our laboratory. If confirmed, this finding would complement previous observations that transcription of S. cerevisiae PGK increases on heat-shock (Piper et al. (1986) Eur. 1. Bioc/zem., 161,525-531). Thus the PGK gene could be implicated as being one of the genes that are induced as part of the general stress response of S. cerevisiae.