Formation of active nitrite reductase (cytochromecd 1) in the strainParacoccus denitrificans HUUG25

Strain HUUG25 ofParacoccus denitrificans has been frequently thought to be devoid of allc-type cytochromes. We show here by means of enzymological and immunological techniques that the mutant synthesizes active nitrite reductase (cytochromecd ₁) upon prolonged exposure to microoxic conditions. The synthesis occurred faster in the presence of exogenous hemin. The time pattern of 5-aminolevulinate synthase activity was also altered by the mutation. These findings suggest a defective regulation of heme supply to the site of nitrite reductase assembly in the periplasm.