APPLICATION OF INHIBITOR TITRATIONS FOR THE DETECTION OF OXIDATIVE-PHOSPHORYLATION DEFECTS IN SAPONIN-SKINNED MUSCLE-FIBERS OF PATIENTS WITH MITOCHONDRIAL DISEASES

Inhibitor titrations were applied to characterize functional changes i n mitochondrial energy metabolism in the skeletal muscle of patients w ith mitochondrial diseases. For this we titrated the maximal mitochond rial respiration rate of saponin-skinned muscle fibers isolated from t he skeletal muscle biopsy with the specific inhibitors of mitochondria l oxidative phosphorylation complexes I, IV and V-rotenone, azide and oligomycin. For three patients with deletions of mitochondrial DNA and one patient with a complex I deficiency the titrations revealed at ra ther normal respiration activities of saponin-skinned fibers significa nt differences to healthy controls: (i) The inhibitor titration curves of the affected enzyme were much steeper and (ii) for almost complete inhibition of respiration a smaller amount of the inhibitor is necess ary, The detailed analysis of the titration curves within the framewor k of metabolic control theory indicated elevated flux control coeffici ents of the respective complex of respiratory chain. On the other hand , for one patient with a mitochondrial DNA depletion syndrome, decreas ed respiration activities of skinned fibers but no redistribution of f lux control was observed. We conclude, therefore, that application of inhibitor titrations and the quantitative description of the titration curve can be a valuable approach to elucidate functional defects of m itochondrial oxidative phosphorylation.