Respiration-induced Changes in the Adenine Nucleotide Pool Composition of Harvested Beneckea natriegens

Abstract

Changes in adenine nucleotide composition of suspensions of starved Beneckea natriegens on aeration and anaerobiosis have been studied using succinate as the respiratory substrate. The anaerobic steady-state adenylate pool is only about 50 to 60 % of the aerobic steady-state pool, and the energy charge is also much lower under anaerobic conditions. Aeration of anaerobic suspensions causes the ATP and total adenylate concentrations and the energy charge to rise rapidly with an overshoot in the ATP concentration before the aerobic steady-state is attained. Shifts to anaerobic conditions result in oscillations of the energy charge and adenine nucleotide concentration and the anaerobic steady-state is only attained relatively slowly. Sequential aeration and anaerobiosis stabilizes the adenine nucleotide pool size, permitting estimates of P/O ratios. The P/O ratio, with succinate as the respiratory substrate, has been assayed by pulsing anaerobic suspensions with small amounts of oxygen (generated from H2O2 and catalase) and quenching metabolic activity before anaerobiosis had been regained, then analysing the adenine nucleotide composition. P/O ratios of 0·2 decreasing to 0·02 with increasing oxygen pulse size have been observed. Extrapolation to zero pulse size, when little turnover of the adenylates occurs, gives a P/O ratio of about 0·4. This is much lower than the efficiency of energy transduction as indicated from H+/O experiments. Therefore, either the observed and extrapolated P/O ratios are unrealistically low and further correction is required, or only a small proportion of the energy transduction is involved in phosphorylation under these conditions.