Anaerobic Respiration and Energy Conservation inParacoccus denitrficans

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Abstract
1 Electron paramagnetic resonance spectra at 8–60 K of NADH-reduced membrane particles prepared from Paracoccus denitrificans grown anaerobically with nitrate as terminal electron acceptor show the presence of iron-sulfur centers 1–4 in the NADH-ubiquinone segment of the respiratory chain. In addition resonance lines at g= 2.058, g= 1.953 and g= 1.88 are detectable in the spectra of succinate-reduced membranes at 15 K, which are attributed to the iron-sulfur-containing nitrate reductase. 2 Sulphate-limited growth under anaerobic conditions does not affect the iron-sulfur pattern of NADH dehydrogenase or nitrate reductase. Furthermore respiratory chain-linked electron transport and its inhibition by rotenone are not influenced. These results contrast those observed for sulphate-limited growth of P. denitrificans under aerobic conditions [Eur. J. Biochem. (1977) 81, 267–275]. 3 Proton translocation studies of whole cells indicate that nitrite increases the proton conductance of the cytoplasmic membrane, resulting in a collapse of the proton gradient across the membrane. Nitrite accumulates under anaerobic growth conditions with nitrate as terminal electron acceptor; the extent of accumulation depends on the specific growth conditions. Thus the low efficiencies of respiratory chain-linked energy conservation observed during nitrate respiration [Arch. Microbiol. (1977) 112, 17–23] can be explained by the uncoupling action of nitrite.