Crystalline Pseudomonas cytochrome oxidase. I. Enzymic properties with special reference to the biological specificity.

Abstract The crystalline preparation of Pseudomonas cytochrome oxidase has two activities: a cytochrome oxidase and a nitrite reductase activity. One mole of the enzyme aerobically oxidizes 154 moles and 600 moles of reduced Pseudomonas cytochrome c -551 per min, at 16 c and 27°, respectively. Anaerobically, 250 moles of reduced Pseudomonas cytochrome c -551 were oxidized per min per mole of enzyme, in the presence of nitrite, at 19°. The absorption spectrum of the enzyme showed that both haem a 2 and a c -type haem are present on the molecule. The enzyme has a strict biological specificity: it oxidizes reduced Pseudomonas cytochrome c -551, but scarcely acts on reduced mammalian cytochrome c . These properties of the enzyme were used to detect slight differences between c -type cytochromes. Reduced tunny-fish cytochrome c was oxidized by the enzyme more rapidly than reduced beef cytochrome c . The reduced form of Physarum polycephalum cytochrome c was not oxidized by the enzyme, but was oxidized by cytochrome a . Reduced wheat cytochrome c was oxidized faster by cytochrome a than by Pseudomonas cytochrome oxidase. Reduced Porphyra tenera cytochrome-553 was oxidized by Pseudomonas cytochrome oxidase, but not by cytochrome a . It is suggested that the oxidizability of the c -type cytochromes by Pseudomonas cytochrome oxidase offers a molecular basis for the taxonomy and evolution of organisms.