The reaction of cytochrome oxidase with cyanide.

The ability of cyanide to inhibit the oxygen consumption of biological systems has long been known (cf. (4, 13)). Warburg (12, 13) appears to be the first to suggest that this action of cyanide was due t,o its combination with the ferric form of the enzyme, called by hi the Atmungaferment and later called cytochrome oxidase by Keilin and Hartree (5). In this paper we make use of this reaction of cyanide with cytochrome oxidase to obtain some quantitative spectroscopic data on the reduced form of this enzyme and to draw certain conclusions concerning the nature of this enzyme whose positive identification has been somewhat elusive.