COMPENSATORY ELEVATION OF COMPLEX-II ACTIVITY IN LEBERS HEREDITARY OPTIC NEUROPATHY

Aims - To evaluate the mitochondrial respiratory enzyme activities in blood cells of Lebers hereditary optic neuropathy (LHON) with 11778 po int mutation of mitochondrial DNA. Methods - Assays for the activities of NADH-cytochrome c reductase (complex I + complex III), succinate-c ytochrome c reductase (complex II + complex III), and cytochrome c oxi dase (complex IV) on blood cell mitochondria of seven LHON patients an d 15 normal controls. Results - There was no statistically significant difference in NADH-cytochrome c reductase and cytochrome c oxidase ac tivities between LHON patients and controls, but activities of succina te-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 succinat e-cytochrome c reductase is increased in LHON patients with 11778 poin t mutation of mitochondrial DNA indicate an elevation of complex II ac tivity, which may be due to a nuclear compensatory effect for defects of the respiratory function of mitochondria.