Effect of O2, H2 and redox potential on the activity and synthesis of hydrogenase 2 in Escherichia coli

The aim of this work was to study the influence of O-2 with special emphasis on low oxygen tension, the effect of H-2 under various conditions of oxygen tension and the influence of the redox potential in the growth medium on hydrogenase 2 of Escherichia coli. The hydrogenase activity and the content of the large (HybC) and small (Hyb0) subunits of hydrogenase 2 were compared during turbidostat cultivation in a wild strain and mutant HDK103 lacking hydrogenases 1 and 3. No hydrogenase 2 activity in the mutant HDK103 was observed under aerobic conditions, but it was maximal under anaerobic conditions and half-maximal at an oxygen tension of similar to4 mbar as is common for enzymes of anaerobic respiration. The content of hydrogenase 2 in both the strains was-maximal under anaerobic conditions. In the wild strain, H-2 addition enhanced hydrogenase activity and the Hyb0 content under microaerobic conditions only. Under anaerobic conditions endogenous H-2 production hindered this effect. Under aerobic conditions, the O-2-related negative effect seemed to dominate over the H-2-related positive effect. By contrast, in the mutant HDK103, hydrogen influenced neither hydrogenase 2 activity nor its content. A possible role of hydrogenase 1 in the response of hydrogenase 2 to hydrogen is discussed. Under conditions of different O-2 tension, hydrogenase activity in both strains correlated inversely with the value of the redox potential of the medium. The presence of H-2 changed this dependence. Thus, the value of the redox potential itself is not a controlling factor for hydrogenase 2. (C) 2001 Editions scientifiques et medicales Elsevier SAS.