Low Activities of the Pyruvate and Oxoglutarate Dehydrogenase Complexes in Five Patients with Friedreich's Ataxia

Abstract

Since patients with Friedreich's ataxia appear to oxidize pyruvate slowly, we measured the activity of the pyruvate dehydrogenase complex in disrupted fibroblasts from four patients with this syndrome and one patient with a clinical variant. The activity was 43 +/- 4 per cent of that in 16 controls (mean +/- S.E.M., P less than 0.001). The activity of the 2-oxoglutarate dehydrogenase complex was also lower in the patients' cells than in those of controls (50 +/- 2 per cent, P less than 0.001). However, the activity of cytochrome-c oxidase was normal (126 +/- 43 per cent of controls). Mixing experiments gave no evidence of soluble enzyme inhibitors or activators, and the addition of excess substrate or cofactor did not ameliorate the deficiencies. White blood cells from one of the patients had low activities of both complexes. Mutations of these dehydrogenase complexes occur in some patients with Friedreich's ataxia and lead to abnormally low activity of an enzyme of the tricarboxylic acid cycle.

Frataxin activates mitochondrial energy conversion and oxidative phosphorylation

“…3f ). This approach showed no difference in the amount of mitochondria, an observation consistent with previously published data obtained in muscle extracts from FA patients (45). Furthermore, Western blot analysis of cytochrome c content in the mitochondrial fractions of both cell lines indicated no difference in mitochondrial biogenesis (data not shown).…”

“…To test this hypothesis in viable mitochondria, we measured calcium transport into isolated mitochondria as previously described (47). Dynamic 45 Ca 2ϩ -uptake was increased by 2.2-fold (P Ͻ 0.001) (Fig. 2f, right pair of bars), an effect which could be blocked by preincubation with ruthenium red (Fig.…”

“…The final pellet was resuspended in MSH buffer and kept on ice for further experiments. 45 Ca 2ϩ -uptake of isolated mitochondria was monitored by the radioisotope technique (40). Briefly, mitochondria (0.5 mg͞ml) were incubated at 25°C in 1 ml of MSH buffer (as above) with continuous stirring.…”

“…Where indicated, ruthenium red (Sigma), a specific inhibitor of mitochondrial Ca 2ϩ -uptake (41), was added (final concentration: 2 nmol͞mg mitochondrial protein). One minute after addition of rotenone and succinate, Ca 2ϩ -uptake was initiated by addition of 200 M Ca 2ϩ with 45 Ca 2ϩ (2000 dpm͞nmol) as tracer. To induce Ca 2ϩ -efflux, 5 mM EGTA (Sigma) was added 5 min after addition of Ca 2ϩ (42).…”

Zn2+ Inhibits α-Ketoglutarate-stimulated Mitochondrial Respiration and the Isolated α-Ketoglutarate Dehydrogenase Complex

“…One component of energy metabolism that has been extensively studied is the ␣-ketoglutarate dehydrogenase complex (KGDHC). 1 Reductions in KGDHC activity or protein abundance in brain occur in several neurological diseases (25)(26)(27)(28)(29)(30). The cause of this deficit has not been established.…”