Comparison of energization of complex I in membrane particles from Paracoccus denitrificans and bovine heart mitochondria.
The results of preliminary studies of the effects of energization on the catalytic and EPR properties of complex I in tightly coupled membrane vesicles of Paracoccus denitrificans (SPP) are presented. They are compared to those observed in submitochondrial particles from bovine heart (SMP). All signs of energization of complex I detected by EPR in SMP (uncoupler-sensitive splitting of the gz lines of the clusters 2 and a broadening of their gxy lines, a fast-relaxing, piericidin-sensitive ubiquinone-radical signal, and a broad signal around g = 1.94) were also observed with the bacterial enzyme. There were some prominent differences, though. The signal of the fast-relaxing radicals could be evoked both in the presence or absence of reduced clusters 2, suggesting that enhancement of its spin-relaxation rate is caused by coupling to another paramagnet. The signal was hardly affected by the presence of gramicidin. The slow-relaxing radical signal did not disappear upon anaerobiosis, but was detectable for at least another 30 s. The fast-relaxing signal vanished immediately upon anaerobiosis. The activity of the bacterial enzyme during oxidation of NADH by oxygen or reduction of NAD induced by succinate oxidation, was 5-6 times higher than that of the mitochondrial enzyme. Unlike the mitochondrial enzyme, the bacterial enzyme was not inactivated by incubation at 35 degrees C. The spin concentration of the NADH-reducible [2Fe-2S] cluster (1b) was half that of the clusters 2, indicating no difference with the mitochondrial enzyme.
Kotlyar
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Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv, Israel.
Albracht
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SP
van Spanning
R J
RJ
D000818:Animals; D002384:Catalysis; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy; D008566:Membranes / Q000378:metabolism; D008929:Mitochondria, Heart / Q000201:enzymology*; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism*; D010231:Paracoccus denitrificans / Q000201:enzymology*; D013816:Thermodynamics
D016660:NAD(P)H Dehydrogenase (Quinone)