No 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 + III, 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 n M CuSO4. Fumarase activity was not affected by copper supplementation, but the complex I + III: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 electron transfer activity of copper-independent complex I + III 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.