Details

Autor(en) / Beteiligte

• Chang, Chu-cheng Eric

Titel

Biochemical and genetic analysis of dioxygen effects on copper, zinc superoxide dismutase mutants in Saccharomyces cerevisiae

Ort / Verlag

ProQuest Dissertations Publishing

Erscheinungsjahr

1989

Link zum Volltext

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• Yeast (Saccharomyces cerevisiae) strains carrying scd1 allele do not express functional Cu,Zn superoxide dismutase (Cu, Zn-SOD, SOD-1). They were used to study the role played by SOD-1. scd1 was at the locus of SOD1 and was mapped ca 9 cM proximal to cdc11 on chromosome X. Thus, scdl is designated as sod1-1. Strains carrying sod1-1 did not grow in pure O$\sb2$ in rich medium, were Met and Lys auxotrophic in air, but grew in acetate. The SOD-1 polypeptide(s) derived from the sod1-1 was enzymatically inactive which may be due to an impaired dimerization of monomers and/or an inability to bind Cu. The O$\sb2$-intolerance were rescued by either transformation with a SOD1-plasmid or accumulation of Mn$\sp{2+}$ in cell. Both treatments increased cytosolic O$\sb{2-}$ scavenging activity yet did not elevate the activities of other antioxidant enzymes. Increasing activity of catalase T alone or of catalases and Mn-SOD (SOD-2) did not rescue the O$\sb2$ intolerance. These results indicate that cytosolic O$\sb{2-}$ scavenging activity is required specifically for O$\sb2$ tolerance. SOD-1 and SOD-2 (Mn-SOD, mitochondrial) are catalytically identical, but SOD-1$\sp-$ and SOD-2$\sp -$ strains displayed different phenotypes. The SOD-2$\sp -$ strain grew slowly in pure O$\sb2$ in rich medium, displayed no O$\sb2$-dependent auxotrophy, but did not grow in acetate. These observations suggest that cellular compartment-specific and O$\sb2$-dependent damage may be protected by the SOD in that compartment. That is, SOD-1, which is located in the cytosol, could protect against a cytosolic damage. Indeed, the O$\sb2$-dependent Met auxotrophy in the sod1-1 carrying mutant correlated to an inability to reduce SO$\sb4\sp{2-}$ to S$\sp{2-}$, a process which takes place in the yeast cytosol. Furthermore, while no apparent defect was found at the level of either sulfite reductase or the formation of 3$\prime$-phospho-adenosine-5$\prime$-phosphosulfate from SO$\sb4\sp{2-}$, SOD-1$\sp -$ strains were more sensitive than any SOD-1$\sp +$ strain to $\mu$M SO$\sb3\sp{2-}$ in an O$\sb2$-dependent fashion. This result suggests that the aerobic metabolism of SO$\sb3\sp{2-}$ (or SO$\sb4\sp{2-}$) in yeast in the absence of SOD-1 produces some toxic compound which can be correlated to the O$\sb2$-dependent Met auxotrophy.