REGULATION OF OXIDATIVE-PHOSPHORYLATION - THE FLEXIBLE RESPIRATORY NETWORK OF PARACOCCUS-DENITRIFICANS

Paracoccus denitrificans is a facultative anaerobic bacterium that has the capacity to adjust its metabolic infrastructure, quantitatively a nd/or qualitatively, to the prevailing growth condition. In this bacte rium the relative activity of distinct catabolic pathways is subject t o a hierarchical control. In the presence of oxygen the aerobic respir ation, the most efficient way of electron transfer-linked phosphorylat ion, has priority. At high oxygen tensions P. denitrificans synthesize s an oxidase with a relatively low affinity for oxygen, whereas under oxygen limitation a high-affinity oxidase appears specifically induced . During anaerobiosis, the pathways with lower free energy-transducing efficiency are induced. In the presence of nitrate, the expression of a number of dehydrogenases ensures the continuation of oxidative phos phorylation via denitrification. After identification of the structura l components that. are involved in both the aerobic and the anaerobic respiratory networks of P. denitrificans, the intriguing next challeng e is to get insight in its regulation. Two transcription regulators ha ve recently been demonstrated to be involved in the expression of a nu mber of aerobic and/or anaerobic respiratory complexes in P. denitrifi cans. Understanding of the regulation machinery is beginning to emerge and promises much excitement in discovery.