Protonophoric activity of NADH coenzyme Q reductase and ATP synthase in coupled submitochondrial particles from horse platelets

Decreased Pasteur effect in platelets of aged individuals

We have investigated the mitochondrial energy state in human platelets of young (19-30 years old) and aged individuals (65-87 years old) exploiting the Pasteur effect, i.e. stimulation of lactate production by incubation of the purified platelets with the mitochondrial respiratory chain inhibitor, antimycin A. This assay allows the determination of mitochondrial function with respect to glycolysis, and the ratio of mitochondrial adenosine triphosphate (ATP) to glycolytic ATP. A significant increase of basal, non-stimulated lactate production and decrease of the stimulation by antimycin A were observed in the older individuals, suggesting that the impairment of oxidative phosphorylation detectable in post-mitotic tissues of aged individuals can be observed also in easily collectable blood cells.

Catalytic activities of mitochondrial ATP synthase in patients with mitochondrial DNA T8993G mutation in the ATPase 6 gene encoding subunit a

We investigated the biochemical phenotype of the mtDNA T8993G point mutation in the ATPase 6 gene, associated with neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP), in three patients from two unrelated families. All three carried >80% mutant genome in platelets and were manifesting clinically various degrees of the NARP phenotype. Coupled submitochondrial particles prepared from platelets capable of succinate-sustained ATP synthesis were studied using very sensitive and rapid luminometric and fluorescence methods. A sharp decrease (>95%) in the succinate-sustained ATP synthesis rate of the particles was found, but both the ATP hydrolysis rate and ATP-driven proton translocation (when the protons flow from the matrix to the cytosol) were minimally affected. The T8993G mutation changes the highly conserved residue Leu(156) to Arg in the ATPase 6 subunit (subunit a). This subunit, together with subunit c, is thought to cooperatively catalyze proton translocation and rotate, one with respect to the other, during the catalytic cycle of the F(1)F(0) complex. Our results suggest that the T8993G mutation induces a structural defect in human F(1)F(0)-ATPase that causes a severe impairment of ATP synthesis. This is possibly due to a defect in either the vectorial proton transport from the cytosol to the mitochondrial matrix or the coupling of proton flow through F(0) to ATP synthesis in F(1). Whatever mechanism is involved, this leads to impaired ATP synthesis. On the other hand, ATP hydrolysis that involves proton flow from the matrix to the cytosol is essentially unaffected.