The rate of carbon dioxide production in the ADH II-deficient strain was found to be 101.5 (��5.9) % of that in Zm6. Thus, apart from the ADH reaction, the other selleck chem Navitoclax catabolic fluxes, producing or consuming NAD(P)H, were not altered in the mutant strain.Table 1Oxygen uptake rates of cells and cytoplasmic membrane vesicles. Cells grown overnight without aeration were used for the whole-cell experiments and membrane preparation. Oxygen uptake measurements in membrane preparations were carried out in 50mM …3.2. Catalase Activity and H2O2 Generation in the Mutant StrainIt is well established that ADH II is a major stress protein in Z. mobilis, induced by high ethanol concentrations and elevated temperature [30].

Although ADH II itself is sensitive to oxygen due to presence of Fe2+ in its active site [31], participation of bacterial iron-containing ADH isoenzymes in the oxidative stress protection has been suggested previously. For E. coli, Echave et al. [32] showed deleterious effects of the iron-containing isoenzyme (AdhE) deficiency on aerobic growth, leading to morphologic defects and inability to grow aerobically on minimal media. They proposed that AdhE acts as an intracellular H2O2 scavenger, in particular at low or medium hydrogen peroxide concentrations. In order to find out if Z. mobilis ADH II also functions in the intracellular H2O2 turnover, we examined the excretion of hydrogen peroxide in the incubation medium of cell suspensions, as well as measured catalase activity in both strains (Figure 4). Although the transcription of catalase gene in Z.

mobilis has been reported not to depend on aeration [33], catalase activity in aerobically cultivated parent strain was significantly higher (P < 0.05), than in anaerobically grown cells. Remarkably, under anaerobic batch culture conditions there was no statistically significant difference between the catalase activity in the parent and mutant strain, yet during aerobic batch cultivation catalase activity in the mutant strain dramatically increased, in the stationary phase cells exceeding that of the parent strain by a factor of three (Figure 4(a)). At the same time, aerobically grown glucose-consuming mutant cells excreted more hydrogen peroxide, in spite of the elevated catalase activity. The rate of hydrogen peroxide excretion GSK-3 in aerobically grown mutant cells was significantly higher than in Zm6 (P < 0.05). It exceeded the H2O2 excretion in the parent strain by about 50%, while no statistically significant difference in H2O2 production was found between anaerobically grown cells of both strains (Figure 4(b)).