Regulation of reductase formation in Proteus mirabilis II. Influence of growth with azide and of haem deficiency on nitrate reductase formation

Abstract

1. 1. Nitrate reductase A (EC 1.9.6.1) of Proteus mirabilis was formed under anaerobic conditions in the presence of nitrate or nitrite and, in large amounts, after anaerobic growth in the presence of azide. Nitrate reductase was submitted to repression and inactivation by oxygen. The formation of the enzyme was depressed when a culture growing aerobically was shifted to anaerobic conditions, altuough nitrate was absent. A δ-aminolaevulinate-deficient mutant formed nitrate reductase A under anerobic conditions after transfer to medium without δ-aminolaevulinate and nitrate. A shift to aerobic conditions hereafter did not result in an activation of nitrate reductase. 2. 2. During anaerobic growth with azide the formation of formate hydrogenlyase was strongly repressed, whereas the formation of methylene blue-linked formate dehydrogenase (EC 1.2.2.1), benzyl viologen-linked formate dehydrogenase, and hydrogenase (EC 1.98.1.1.) was not influenced significantly. Azide strongly inhibited the activities of formate hydrogenlyase and benzyl viologen-linked formate dehydrogenase but not those of hydrolynase and methylene blue-linked formate dehydrogenase. 3. 3. Proteus mirabilis can form different b-type cytochromes. The level of cytochrome b 599, which is involved in nitrate reduction, was greatly enlarged after anaerobic growth with azide. Similarly, the formate-nitrate reductase A activity was much higher after growth with azide. It is concluded that nitrate reductase A is formed as a component of a complex containing formate dehydrogenase, cytochrome b 559 and nitrate reductase.