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J Biol Chem, Vol. 274, Issue 39, 27590-27596, September 24, 1999
§,
From the The absence of the antioxidant enzyme
Cu,Zn-superoxide dismutase (SOD1) is shown here to cause vacuolar
fragmentation in Saccharomyces cerevisiae. Wild-type yeast
have 1-3 large vacuoles whereas the sod1
Predoctoral Program in Human Genetics, Johns
Hopkins University, Baltimore, Maryland 21205, the
§ Ludwig Institute for Cancer Research, La Jolla, California
92093, the ¶ Department of Environmental Health Sciences, Johns
Hopkins School of Hygiene and Public Health, Baltimore, Maryland 21205, and the
Departments of Medicine and Neuroscience, University
of California at San Diego, La Jolla, California 92093
yeast have as
many as 50 smaller vacuoles. Evidence that this fragmentation is
oxygen-mediated includes the findings that aerobically (but not
anaerobically) grown sod1
yeast exhibit aberrant
vacuoles and genetic suppressors of other oxygen-dependent sod1 null phenotypes rescue the vacuole defect.
Surprisingly, iron also is implicated in the fragmentation process as
iron addition exacerbates the sod1
vacuole defect while
iron starvation ameliorates it. Because the vacuole is reported to be a
site of iron storage and iron reacts avidly with reactive oxygen
species to generate toxic side products, we propose that vacuole damage
in sod1
cells arises from an elevation of iron-mediated
oxidation within the vacuole or from elevated pools of "free" iron
that may bind nonproductively to vacuolar ligands. Furthermore,
additional pleiotropic phenotypes of sod1
cells
(including increased sensitivity to pH, nutrient deprivation, and
metals) may be secondary to vacuolar compromise. Our findings support
the hypothesis that oxidative stress alters cellular iron homeostasis
which in turn increases oxidative damage. Thus, our findings may have
medical relevance as both oxidative stress and alterations in iron
homeostasis have been implicated in diverse human disease processes.
Our findings suggest that strategies to decrease intracellular iron may
significantly reduce oxidatively induced cellular damage.
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