Compensatory elevation of complex II activity in Leber's hereditary optic neuropathy.

AIMS To evaluate the mitochondrial respiratory enzyme activities in blood cells of Leber's hereditary optic neuropathy (LHON) with 11778 point mutation of mitochondrial DNA. METHODS Assays for the activities of NADH-cytochrome c reductase (complex I+complex III), succinate-cytochrome c reductase (complex II+complex III), and cytochrome c oxidase (complex IV) on blood cell mitochondria of seven LHON patients and 15 normal controls. RESULTS There was no statistically significant difference in NADH-cytochrome c reductase and cytochrome c oxidase activities between LHON patients and controls, but activities of succinate-cytochrome c reductase in LHON patients was significantly elevated compared with normal controls. CONCLUSION The observations that the activity of NADH-cytochrome c reductase is normal but that of succinate-cytochrome c reductase is increased in LHON patients with 11778 point mutation of mitochondrial DNA indicate an elevation of complex II activity, which may be due to a nuclear compensatory effect for defects of the respiratory function of mitochondria.