Reconsideration of the efficiency of energy transduction in Paracoccus denitrificans during growth under a variety of culture conditions

Abstract1. Theoretical overall P/2e- ratios were calculated for growth of Paracoccus denitrificans under a variety of culture conditions on the basis of a growth model and recently published schemes of electron transport and associated proton translocation. 2. Experimental overall P/2e- ratios were calculated, using the specific rate of ATP synthesis determined in cultures grown under aerobic carbon source-limited conditions. 3. The experimental P/2e- was equal to the theoretical P/2e- for aerobic sulphate-limited growth with gluconate or succinate as carbon source, on the assumption that site 1 phosphorylation was completely absent. 4. The experimental and the theoretical P/2e- were similar for growth on nitrate as terminal electron acceptor and gluconate, mannitol or succinate as carbon source, on the assumption that nitrate enters the cell via the electroneutral nitrate-nitrite antiport system. 5. The experimental and theoretical P/2e- were similar for growth on nitrite as terminal electron acceptor and mannitol or succinate as carbon source. 6. The experimental P/2e- was substantially lower than the theoretical P/2e- for aerobic growth with nitrate as nitrogen source and gluconate or mannitol as carbon source. The amount of energy needed for assimilative reduction of nitrate to ammonia was calculated from this difference.