Author(s): Orr WC, Arnold LA, Sohal RS
This study was conducted on Drosophila melanogaster mutants with different levels of catalase activity in order to assess the role of antioxidant defenses in the aging process. We present here the analysis of two mutant strains: the catn1/catn4 heterozygote which exhibits no detectable catalase activity and the catn2 homozygote which exhibits approximately 14% that of the parent reference strain. Since insects lack glutathione peroxidase activity, catalase activity provides the sole enzymatic mechanism for the removal of H2O2. Average and maximum life spans of flies were unaffected by the absence or low levels of catalase activity. The mutants however exhibited adaptive responses in their metabolic rate or glutathione content. The metabolic rate of flies was significantly lowered in the null mutants. Glutathione concentration tended to increase in flies with the hypomorphic catalase allele (exhibiting 14% of the normal catalase activity). Gamma-glutamylcysteine synthetase activity was significantly higher in the null flies. Activities of superoxide dismutase and glutathione reductase were unaffected. Results of this study indicate that 14% of the normal level of catalase activity allows flies to achieve both a normal life span and a normal metabolic potential. Small decreases in certain antioxidant defenses, frequently observed during aging, may be functionally not very consequential.