Author
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Johnson, William |
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THOMAS, ANNE - UNIV. OF NORTH DAKOTA |
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Submitted to: American Society for Experimental Biology and Medicine Proceedings
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/3/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Cell proteins, lipids, and DNA are in constant danger of being damaged by chemicals called oxidants that are produced as by-products from the metabolism of the oxygen we breath. Although cells contain defenses that protect them from oxidants, their defenses are not adequate to entirely prevent cellular damage. Because mitochondria are responsible for metabolizing most of the oxygen taken up by cells, they are particularly good targets for oxidant damage. An important component of mitochondrial oxygen metabolism is a copper-containing enzyme called cytochrome c oxidase. When the activity of this copper-containing enzyme is lowered, as is the case during copper deficiency, the production of harmful oxidants by mitochondria is increased. We found that depriving cells of copper lowered cytochrome c oxidase activity and elevated the activity of a manganese-containing enzyme called superoxide dismutase. This manganese containing enzyme helps protect mitochondria from oxidative damage and its content is dependent on mitochondrial oxidant production. Thus, the elevated content of manganese-containing superoxide dismutase indicates that oxidant production was increased by copper deprivation. However, the protection afforded by elevated manganse-containing superoxide dismutase was not sufficient to completely protect the mitochondria and oxidative damage to mitochondrial proteins was potentiated by copper deprivation. The accumulation of oxidative damage to mitochondria can contribute to degenerative heart and brain diseases and even minor deficits in mitochondrial function can cause weakness and impair cognitive function. Therefore, the present study suggests that copper is an important nutrient for health maintenance and slowing the development of degenerative Technical Abstract: Cytochrome c oxidase is the copper-dependent terminal respiratory complex (complex IV) of the mitochondrial electron transport chain whose activity in a variety of tissues is lowered by copper deficiency. Because inhibition of respiratory complexes increases the production of reactive oxygen species by mitochondria, it is possible that copper deficiency increases oxidative stress in mitochondria as a consequence of suppressed cytochrome c oxidase activity. In this study, the activities of respiratory complex I, assayed as NADH:cytochrome c reductase, complex II- III, assayed as succinate:cytochrome c reductase, complex IV, assayed as cytochrome c oxidase, and fumarase were measured in mitochondria from HL- 60 cells that were grown for seven passages in serum free medium that was either unsupplemented or supplemented with 50 nM CuSO4. The complex I:fumarase and complex IV:fumarase ratios were reduced 30% and 50%, respectively, in mitochondria from cells grown in the absence of supplemental copper. This indicates that copper deprivation suppressed the activities of copper-independent complex I as well as copper-dependent complex IV. Manganese superoxide dismutase (MnSOD) content was also increased 49% overall in the cells grown in the absence of supplemental copper. Furthermore, protein carbonyl groups, indicative of oxidative modification, were present in 100 kDa and 90 kDa proteins of mitochondria from copper deprived cells. These findings indicate that in cells grown under conditions of copper deprivation that suppress cytochrome c oxidase activity, oxidative stress in mitochondria is increased sufficiently to induce MnSOD, potentiate protein oxidation, and possibly cause the oxidative inactivation of complex I. |
