Comparison of energization of complex I in membrane particles from Paracoccus denitrificans

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 g(z) lines of the clusters 2 and a broadening of their g(xy) 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°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