Add time:08/05/2019         Source:sciencedirect.com

The influence of growth conditions on the synthesis of cytochrome c552 and the activities of NADH-nitrite oxidoreductase (EC 1.6.6.4) and NADH-cytochrome c oxidoreductase (EC 1.6.99.3) have been studied in Escherichia coli strain K12. Nitrite added to anaerobic cultures stimulated cytochrome c552 synthesis as well as nitrite and cytochrome c reductase activities. These were decreased by high concentrations of glucose or amino acids, and were low or absent in aerobically grown cells.When cells were suspended in sucrose and lysozyme (EC 3.2.1.17), and EDTA added, 80% of the cytochrome c552 was released into solution. The NADH-nitrite oxidoreductase activity remaining in the osmotically sensitive spheres so formed was the same as in untreated cells. Nitrite reductase activity and cytochrome c552 were also separated by gel filtration, and by (NH4)2SO4 fractionation. When cytochrome-rich fractions were recombined with nitrite reductase active fractions, no stimulation of the rate of NADH oxidation by nitrite was observed. In every experiment cytochrome c reductase and nitrite reductase activities were found in the same fractions in approximately the same ratio.Both reductases showed substrate inhibition with respect to NADH: the pH optima were 7.9 for nitrite reductase and 8.6 for cytochrome c reductase. It is suggested that cytochrome c reductase activity is due to a lack of specificity of nitrite reductase for an electron acceptor, and that cytochrome c552 is not a physiological intermediate in either reaction. An alternative function for cytochrome c552 in nitrite reduction has been suggested.

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